rfc9776.original   rfc9776.txt 
Network Working Group B. Haberman, Ed. Internet Engineering Task Force (IETF) B. Haberman, Ed.
Internet-Draft JHU APL Request for Comments: 9776 JHU APL
Obsoletes: 3376 (if approved) 27 August 2024 STD: 100 March 2025
Updates: 2236 (if approved) Obsoletes: 3376
Intended status: Standards Track Updates: 2236
Expires: 28 February 2025 Category: Standards Track
ISSN: 2070-1721
Internet Group Management Protocol, Version 3 Internet Group Management Protocol, Version 3
draft-ietf-pim-3376bis-12
Abstract Abstract
IGMP is the protocol used by IPv4 systems to report their IP The Internet Group Management Protocol (IGMP) is the protocol used by
multicast group memberships to neighboring multicast routers. IPv4 systems to report their IP multicast group memberships to
Version 3 of IGMP adds support for source filtering, that is, the neighboring multicast routers. Version 3 of IGMP (IGMPv3) adds
ability for a system to report interest in receiving packets only support for source filtering, that is, the ability for a system to
from specific source addresses, or from all but specific source report interest in receiving packets only from specific source
addresses, sent to a particular multicast address. That information addresses, or from all but specific source addresses, sent to a
may be used by multicast routing protocols to avoid delivering particular multicast address. That information may be used by
multicast packets from specific sources to networks where there are multicast routing protocols to avoid delivering multicast packets
no interested receivers. from specific sources to networks where there are no interested
receivers.
This document specifies Version 3 of the Internet Group Management This document specifies IGMPv3. It is a revised version of RFC 3376
Protocol, IGMPv3. It is a revised version of the specification to that includes clarifications and fixes for errata, and it is backward
include clarifications and fixes for errata in RFC 3376 and is compatible with RFC 3376.
backwards compatible with RFC 3376.
This document updates RFC 2236 and obsoletes RFC 3376. This document updates RFC 2236 and obsoletes RFC 3376.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet Standards is available in Section 2 of RFC 7841.
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and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9776.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
1.1. Conventions Used in This Document . . . . . . . . . . . . 5 1.1. Conventions Used in This Document
2. The Service Interface for Requesting IP Multicast 2. The Service Interface for Requesting IP Multicast Reception
Reception . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Multicast Reception State Maintained by Systems
3. Multicast Reception State Maintained by Systems . . . . . . . 7 3.1. Socket State
3.1. Socket State . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Interface State
3.2. Interface State . . . . . . . . . . . . . . . . . . . . . 8 4. Message Formats
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Membership Query Message
4.1. Membership Query Message . . . . . . . . . . . . . . . . 11 4.1.1. Max Resp Code
4.1.1. Max Resp Code . . . . . . . . . . . . . . . . . . . . 12 4.1.2. Checksum
4.1.2. Checksum . . . . . . . . . . . . . . . . . . . . . . 12 4.1.3. Group Address
4.1.3. Group Address . . . . . . . . . . . . . . . . . . . . 12 4.1.4. Flags
4.1.4. Flags . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1.5. S Flag (Suppress Router-Side Processing)
4.1.5. S Flag (Suppress Router-Side Processing) . . . . . . 13 4.1.6. QRV (Querier's Robustness Variable)
4.1.6. QRV (Querier's Robustness Variable) . . . . . . . . . 13 4.1.7. QQIC (Querier's Query Interval Code)
4.1.7. QQIC (Querier's Query Interval Code) . . . . . . . . 13 4.1.8. Number of Sources (N)
4.1.8. Number of Sources (N) . . . . . . . . . . . . . . . . 14 4.1.9. Source Address [i]
4.1.9. Source Address [i] . . . . . . . . . . . . . . . . . 14 4.1.10. Additional Data
4.1.10. Additional Data . . . . . . . . . . . . . . . . . . . 14 4.1.11. Query Variants
4.1.11. Query Variants . . . . . . . . . . . . . . . . . . . 14 4.1.12. IP Destination Addresses for Queries
4.1.12. IP Destination Addresses for Queries . . . . . . . . 15 4.2. Version 3 Membership Report Message
4.2. Version 3 Membership Report Message . . . . . . . . . . . 15 4.2.1. Reserved
4.2.1. Reserved . . . . . . . . . . . . . . . . . . . . . . 17 4.2.2. Checksum
4.2.2. Checksum . . . . . . . . . . . . . . . . . . . . . . 17 4.2.3. Flags
4.2.3. Flags . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2.4. Number of Group Records (M)
4.2.4. Number of Group Records (M) . . . . . . . . . . . . . 17 4.2.5. Group Record
4.2.5. Group Record . . . . . . . . . . . . . . . . . . . . 18 4.2.6. Record Type
4.2.6. Record Type . . . . . . . . . . . . . . . . . . . . . 18 4.2.7. Aux Data Len
4.2.7. Aux Data Len . . . . . . . . . . . . . . . . . . . . 18 4.2.8. Number of Sources (N)
4.2.8. Number of Sources (N) . . . . . . . . . . . . . . . . 18 4.2.9. Multicast Address
4.2.9. Multicast Address . . . . . . . . . . . . . . . . . . 18 4.2.10. Source Address [i]
4.2.10. Source Address [i] . . . . . . . . . . . . . . . . . 18 4.2.11. Auxiliary Data
4.2.11. Auxiliary Data . . . . . . . . . . . . . . . . . . . 18 4.2.12. Additional Data
4.2.12. Additional Data . . . . . . . . . . . . . . . . . . . 19 4.2.13. Group Record Types
4.2.13. Group Record Types . . . . . . . . . . . . . . . . . 19 4.2.14. IP Source Addresses for Reports
4.2.14. IP Source Addresses for Reports . . . . . . . . . . . 21 4.2.15. IP Destination Addresses for Reports
4.2.15. IP Destination Addresses for Reports . . . . . . . . 21 4.2.16. Notation for Group Records
4.2.16. Notation for Group Records . . . . . . . . . . . . . 21 4.2.17. Membership Report Size
4.2.17. Membership Report Size . . . . . . . . . . . . . . . 22 5. Description of the Protocol for Group Members
5. Description of the Protocol for Group Members . . . . . . . . 22 5.1. Action on Change of Interface State
5.1. Action on Change of Interface State . . . . . . . . . . . 23 5.2. Action on Reception of a Query
5.2. Action on Reception of a Query . . . . . . . . . . . . . 26 6. Description of the Protocol for Multicast Routers
6. Description of the Protocol for Multicast Routers . . . . . . 28 6.1. Conditions for IGMP Queries
6.1. Conditions for IGMP Queries . . . . . . . . . . . . . . . 29 6.2. IGMP State Maintained by Multicast Routers
6.2. IGMP State Maintained by Multicast Routers . . . . . . . 30 6.2.1. Definition of Router Filter-Mode
6.2.1. Definition of Router Filter-Mode . . . . . . . . . . 30 6.2.2. Definition of Group Timers
6.2.2. Definition of Group Timers . . . . . . . . . . . . . 31 6.2.3. Definition of Source Timers
6.2.3. Definition of Source Timers . . . . . . . . . . . . . 32 6.3. IGMPv3 Source-Specific Forwarding Rules
6.3. IGMPv3 Source-Specific Forwarding Rules . . . . . . . . . 33 6.4. Action on Reception of Reports
6.4. Action on Reception of Reports . . . . . . . . . . . . . 34 6.4.1. Reception of Current-State Records
6.4.1. Reception of Current-State Records . . . . . . . . . 34
6.4.2. Reception of Filter-Mode-Change and Source-List-Change 6.4.2. Reception of Filter-Mode-Change and Source-List-Change
Records . . . . . . . . . . . . . . . . . . . . . . . 36 Records
6.5. Switching Router Filter-Modes . . . . . . . . . . . . . . 37 6.5. Switching Router Filter-Modes
6.6. Action on Reception of Queries . . . . . . . . . . . . . 38 6.6. Action on Reception of Queries
6.6.1. Timer Updates . . . . . . . . . . . . . . . . . . . . 38 6.6.1. Timer Updates
6.6.2. Querier Election . . . . . . . . . . . . . . . . . . 38 6.6.2. Querier Election
6.6.3. Building and Sending Specific Queries . . . . . . . . 39 6.6.3. Building and Sending Specific Queries
7. Interoperation With Older Versions of IGMP . . . . . . . . . 40 7. Interoperation With Older Versions of IGMP
7.1. Query Version Distinctions . . . . . . . . . . . . . . . 40 7.1. Query Version Distinctions
7.2. Group Member Behavior . . . . . . . . . . . . . . . . . . 40 7.2. Group Member Behavior
7.2.1. In the Presence of Older Version Queriers . . . . . . 40 7.2.1. In the Presence of Older Version Queriers
7.2.2. In the Presence of Older Version Group Members . . . 42 7.2.2. In the Presence of Older Version Group Members
7.3. Multicast Router Behavior . . . . . . . . . . . . . . . . 42 7.3. Multicast Router Behavior
7.3.1. In the Presence of Older Version Queriers . . . . . . 42 7.3.1. In the Presence of Older Version Queriers
7.3.2. In the Presence of Older Version Group Members . . . 43 7.3.2. In the Presence of Older Version Group Members
8. List of Timers, Counters and Their Default Values . . . . . . 45 8. List of Timers, Counters, and Their Default Values
8.1. Robustness Variable . . . . . . . . . . . . . . . . . . . 45 8.1. Robustness Variable
8.2. Query Interval . . . . . . . . . . . . . . . . . . . . . 45 8.2. Query Interval
8.3. Query Response Interval . . . . . . . . . . . . . . . . . 45 8.3. Query Response Interval
8.4. Group Membership Interval . . . . . . . . . . . . . . . . 46 8.4. Group Membership Interval
8.5. Other Querier Present Interval . . . . . . . . . . . . . 46 8.5. Other Querier Present Interval
8.6. Startup Query Interval . . . . . . . . . . . . . . . . . 46 8.6. Startup Query Interval
8.7. Startup Query Count . . . . . . . . . . . . . . . . . . . 46 8.7. Startup Query Count
8.8. Last Member Query Interval . . . . . . . . . . . . . . . 46 8.8. Last Member Query Interval
8.9. Last Member Query Count . . . . . . . . . . . . . . . . . 47 8.9. Last Member Query Count
8.10. Last Member Query Time . . . . . . . . . . . . . . . . . 47 8.10. Last Member Query Time
8.11. Unsolicited Report Interval . . . . . . . . . . . . . . . 47 8.11. Unsolicited Report Interval
8.12. Older Version Querier Present Interval . . . . . . . . . 47 8.12. Older Version Querier Present Interval
8.13. Older Host Present Interval . . . . . . . . . . . . . . . 47 8.13. Older Host Present Interval
8.14. Configuring Timers . . . . . . . . . . . . . . . . . . . 48 8.14. Configuring Timers
8.14.1. Robustness Variable . . . . . . . . . . . . . . . . 48 8.14.1. Robustness Variable
8.14.2. Query Interval . . . . . . . . . . . . . . . . . . . 48 8.14.2. Query Interval
8.14.3. Max Response Time . . . . . . . . . . . . . . . . . 48 8.14.3. Max Response Time
9. Security Considerations . . . . . . . . . . . . . . . . . . . 49 9. Security Considerations
9.1. Query Message . . . . . . . . . . . . . . . . . . . . . . 49 9.1. Query Message
9.2. Current-State Report messages . . . . . . . . . . . . . . 50 9.2. Current-State Report Messages
9.3. State-Change Report Messages . . . . . . . . . . . . . . 51 9.3. State-Change Report Messages
9.4. IPsec Usage . . . . . . . . . . . . . . . . . . . . . . . 52 9.4. IPsec Usage
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52 10. IANA Considerations
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 52 11. References
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 53 11.1. Normative References
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 53 11.2. Informative References
13.1. Normative References . . . . . . . . . . . . . . . . . . 53 Appendix A. Design Rationale
13.2. Informative References . . . . . . . . . . . . . . . . . 54 A.1. The Need for State-Change Messages
Appendix A. Design Rationale . . . . . . . . . . . . . . . . . . 54 A.2. Host Suppression
A.1. The Need for State-Change Messages . . . . . . . . . . . 54 A.3. Switching Router Filter Modes from EXCLUDE to INCLUDE
A.2. Host Suppression . . . . . . . . . . . . . . . . . . . . 55 Appendix B. Summary of Changes from IGMPv2
A.3. Switching Router Filter Modes from EXCLUDE to INCLUDE . . 55 Appendix C. Summary of Changes from RFC 3376
Appendix B. Summary of Changes from IGMPv2 . . . . . . . . . . . 56 Acknowledgments
Appendix C. Summary of Changes from RFC 3376 . . . . . . . . . . 56 Contributors
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 57 Author's Address
1. Introduction 1. Introduction
The Internet Group Management Protocol (IGMP) is used by IPv4 systems The Internet Group Management Protocol (IGMP) is used by IPv4 systems
(hosts and routers) to report their IP multicast group memberships to (hosts and routers) to report their IP multicast group memberships to
any neighboring multicast routers. Note that an IP multicast router any neighboring multicast routers. Note that an IP multicast router
may itself be a member of one or more multicast groups, in which case may itself be a member of one or more multicast groups, in which case
it performs both the multicast router part of the protocol (to it performs both the multicast router part of the protocol (to
collect the membership information needed by its multicast routing collect the membership information needed by its multicast routing
protocol) and the group member part of the protocol (to inform itself protocol) and the group member part of the protocol (to inform itself
and other, neighboring multicast routers of its memberships). and other, neighboring multicast routers of its memberships).
IGMP is also used for other IP multicast management functions, using IGMP is also used for other IP multicast management functions, using
message types other than those used for group membership reporting. message types other than those used for group membership reporting.
This document specifies only the group membership reporting functions This document specifies only the group membership reporting functions
and messages. and messages.
This document specifies Version 3 of IGMP. Version 1, specified in This document specifies Version 3 of IGMP. Version 1, specified in
[RFC1112], was the first widely-deployed version and the first [RFC1112], was the first widely deployed version and the first
version to become an Internet Standard. Version 2, specified in version to become an Internet Standard. Version 2, specified in
[RFC2236], added support for low leave latency, that is, a reduction [RFC2236], added support for low leave latency, that is, a reduction
in the time it takes for a multicast router to learn that there are in the time it takes for a multicast router to learn that there are
no longer any members of a particular group present on an attached no longer any members of a particular group present on an attached
network. Version 3 adds support for source filtering, that is, the network. Version 3 adds support for source filtering, that is, the
ability for a system to report interest in receiving packets only ability for a system to report interest in receiving packets only
from specific source addresses, as required to support Source- from specific source addresses, as required to support Source-
Specific Multicast [RFC3569], or from all but specific source Specific Multicast (SSM) [RFC3569], or from all but specific source
addresses, sent to a particular multicast address. Version 3 is addresses, sent to a particular multicast address. Version 3 is
designed to be interoperable with Versions 1 and 2. designed to be interoperable with Versions 1 and 2.
This document uses SSM-aware to refer to systems that support Source- This document uses "SSM-aware" to refer to systems that support SSM
Specific Multicast (SSM) as defined in [RFC4607]. as defined in [RFC4607].
This document updates [RFC2236] as a proper implementation of Version This document updates [RFC2236] as a proper implementation of Version
3 of IGMP needs to implement Version 2 Report and Leave message 3 of IGMP needs to implement Version 2 Report and Leave message
handling. handling.
This document obsoletes [RFC3376] as it provides clarifications and This document obsoletes [RFC3376] as it provides clarifications and
fixes for errata in RFC 3376. Detailed updates for those changes are fixes for errata in [RFC3376]. Detailed updates for those changes
described in Appendix C. are described in Appendix C.
1.1. Conventions Used in This Document 1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. The Service Interface for Requesting IP Multicast Reception 2. The Service Interface for Requesting IP Multicast Reception
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NOT be less than 64 addresses per list. When an operation causes NOT be less than 64 addresses per list. When an operation causes
the source list size limit to be exceeded, the service interface the source list size limit to be exceeded, the service interface
MUST return an error. MUST return an error.
For a given combination of socket, interface, and multicast address, For a given combination of socket, interface, and multicast address,
only a single filter mode and source list can be in effect at any one only a single filter mode and source list can be in effect at any one
time. However, either the filter mode or the source list, or both, time. However, either the filter mode or the source list, or both,
may be changed by subsequent IPMulticastListen requests that specify may be changed by subsequent IPMulticastListen requests that specify
the same socket, interface, and multicast address. Each subsequent the same socket, interface, and multicast address. Each subsequent
request completely replaces any earlier request for the given socket, request completely replaces any earlier request for the given socket,
interface and multicast address. interface, and multicast address.
Previous versions of IGMP did not support source filters and had a Previous versions of IGMP did not support source filters and had a
simpler service interface consisting of Join and Leave operations to simpler service interface consisting of Join and Leave operations to
enable and disable reception of a given multicast address (from all enable and disable reception of a given multicast address (from all
sources) on a given interface. The equivalent operations in the new sources) on a given interface. The equivalent operations in the new
service interface follow: service interface follow:
The Join operation is equivalent to: The Join operation is equivalent to:
IPMulticastListen ( socket, interface, multicast-address, IPMulticastListen ( socket, interface, multicast-address,
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3.2. Interface State 3.2. Interface State
In addition to the per-socket multicast reception state, a system In addition to the per-socket multicast reception state, a system
must also maintain or compute multicast reception state for each of must also maintain or compute multicast reception state for each of
its interfaces. That state conceptually consists of a set of records its interfaces. That state conceptually consists of a set of records
of the form: of the form:
(multicast-address, filter-mode, source-list) (multicast-address, filter-mode, source-list)
At most one record per multicast-address exists for a given At most, one record per multicast-address exists for a given
interface. This per-interface state is derived from the per-socket interface. This per-interface state is derived from the per-socket
state, but may differ from the per-socket state when different state, but it may differ from the per-socket state when different
sockets have differing filter modes and/or source lists for the same sockets have differing filter modes and/or source lists for the same
multicast address and interface. For example, suppose one multicast address and interface. For example, suppose one
application or process invokes the following operation on socket s1: application or process invokes the following operation on socket s1:
IPMulticastListen ( s1, i, m, INCLUDE, {a, b, c} ) IPMulticastListen ( s1, i, m, INCLUDE, {a, b, c} )
requesting reception on interface i of packets sent to multicast requesting reception on interface i of packets sent to multicast
address m, only if they come from source a, b, or c. Suppose another address m, only if they come from source a, b, or c. Suppose another
application or process invokes the following operation on socket s2: application or process invokes the following operation on socket s2:
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same multicast address m, only if they come from sources b, c, or d. same multicast address m, only if they come from sources b, c, or d.
In order to satisfy the reception requirements of both sockets, it is In order to satisfy the reception requirements of both sockets, it is
necessary for interface i to receive packets sent to m from any one necessary for interface i to receive packets sent to m from any one
of the sources a, b, c, or d. Thus, in this example, the reception of the sources a, b, c, or d. Thus, in this example, the reception
state of interface i for multicast address m has filter mode INCLUDE state of interface i for multicast address m has filter mode INCLUDE
and source list {a, b, c, d}. and source list {a, b, c, d}.
After a multicast packet has been accepted from an interface by the After a multicast packet has been accepted from an interface by the
IP layer, its subsequent delivery to the application or process IP layer, its subsequent delivery to the application or process
listening on a particular socket depends on the multicast reception listening on a particular socket depends on the multicast reception
state of that socket [and possibly also on other conditions, such as state of that socket (and possibly also on other conditions, such as
what transport-layer port the socket is bound to]. So, in the above what transport-layer port the socket is bound to). So, in the above
example, if a packet arrives on interface i, destined to multicast example, if a packet arrives on interface i, destined to multicast
address m, with source address a, it will be delivered on socket s1 address m, with source address a, it will be delivered on socket s1
but not on socket s2. Note that IGMP Queries and Reports are not but not on socket s2. Note that IGMP Queries and Reports are not
subject to source filtering and must always be processed by hosts and subject to source filtering and must always be processed by hosts and
routers. routers.
Filtering of packets based upon a socket's multicast reception state Filtering of packets based upon a socket's multicast reception state
is a new feature of this service interface. The previous service is a new feature of this service interface. The previous service
interface [RFC1112] described no filtering based upon multicast join interface [RFC1112] described no filtering based upon multicast join
state; rather, a join on a socket simply caused the host to join a state; rather, a join on a socket simply caused the host to join a
group on the given interface, and packets destined for that group group on the given interface, and packets destined for that group
could be delivered to all sockets whether they had joined or not. could be delivered to all sockets whether they had joined or not.
The general rules for deriving the per-interface state from the per- The general rules for deriving the per-interface state from the per-
socket state are as follows: For each distinct (interface, multicast- socket state are as follows: For each distinct (interface, multicast-
address) pair that appears in any socket state, a per- interface address) pair that appears in any socket state, a per-interface
record is created for that multicast address on that interface. record is created for that multicast address on that interface.
Considering all socket records containing the same (interface, Considering all socket records containing the same (interface,
multicast-address) pair, multicast-address) pair,
* if any such record has a filter mode of EXCLUDE, then the filter * if any such record has a filter mode of EXCLUDE, then the filter
mode of the interface record is EXCLUDE, and the source list of mode of the interface record is EXCLUDE, and the source list of
the interface record is the intersection of the source lists of the interface record is the intersection of the source lists of
all socket records in EXCLUDE mode, minus those source addresses all socket records in EXCLUDE mode, minus those source addresses
that appear in any socket record in INCLUDE mode. For example, if that appear in any socket record in INCLUDE mode. For example, if
the socket records for multicast address m on interface i are: the socket records for multicast address m on interface i are:
from socket s1: ( i, m, EXCLUDE, {a, b, c, d} ) - from socket s1: ( i, m, EXCLUDE, {a, b, c, d} )
from socket s2: ( i, m, EXCLUDE, {b, c, d, e} ) - from socket s2: ( i, m, EXCLUDE, {b, c, d, e} )
from socket s3: ( i, m, INCLUDE, {d, e, f} ) - from socket s3: ( i, m, INCLUDE, {d, e, f} )
then the corresponding interface record on interface i is: then the corresponding interface record on interface i is:
( m, EXCLUDE, {b, c} ) - ( m, EXCLUDE, {b, c} )
If a fourth socket is added, such as: If a fourth socket is added, such as:
from socket s4: ( i, m, EXCLUDE, {} ) - from socket s4: ( i, m, EXCLUDE, {} )
then the interface record becomes: then the interface record becomes:
( m, EXCLUDE, {} ) - ( m, EXCLUDE, {} )
* if all such records have a filter mode of INCLUDE, then the filter * if all such records have a filter mode of INCLUDE, then the filter
mode of the interface record is INCLUDE, and the source list of mode of the interface record is INCLUDE, and the source list of
the interface record is the union of the source lists of all the the interface record is the union of the source lists of all the
socket records. For example, if the socket records for multicast socket records. For example, if the socket records for multicast
address m on interface i are: address m on interface i are:
from socket s1: ( i, m, INCLUDE, {a, b, c} ) - from socket s1: ( i, m, INCLUDE, {a, b, c} )
from socket s2: ( i, m, INCLUDE, {b, c, d} ) - from socket s2: ( i, m, INCLUDE, {b, c, d} )
from socket s3: ( i, m, INCLUDE, {e, f} )
- from socket s3: ( i, m, INCLUDE, {e, f} )
then the corresponding interface record on interface i is: then the corresponding interface record on interface i is:
( m, INCLUDE, {a, b, c, d, e, f} ) - ( m, INCLUDE, {a, b, c, d, e, f} )
An implementation MUST NOT use an EXCLUDE interface record to An implementation MUST NOT use an EXCLUDE interface record to
represent a group when all sockets for this group are in INCLUDE represent a group when all sockets for this group are in INCLUDE
state. If system resource limits are reached when an interface state. If system resource limits are reached when an interface
state source list is calculated, an error MUST be returned to the state source list is calculated, an error MUST be returned to the
application which requested the operation. application that requested the operation.
The above rules for deriving the interface state are (re-)evaluated The above rules for deriving the interface state are (re-)evaluated
whenever an IPMulticastListen invocation modifies the socket state by whenever an IPMulticastListen invocation modifies the socket state by
adding, deleting, or modifying a per-socket state record. Note that adding, deleting, or modifying a per-socket state record. Note that
a change of socket state does not necessarily result in a change of a change of socket state does not necessarily result in a change of
interface state. interface state.
4. Message Formats 4. Message Formats
IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol
number of 2. Every IGMP message described in this document is sent number of 2. Every IGMP message described in this document is sent
with an IP Time-to-Live of 1, IP Precedence of Internetwork Control with an IP Time-to-Live of 1, IP Precedence of Internetwork Control
(e.g., Type of Service 0xc0), and carries an IP Router Alert option (e.g., Type of Service 0xc0), and carries an IP Router Alert option
[RFC2113] in its IP header. IGMP message types are registered per [RFC2113] in its IP header. IGMP message types are registered per
[I-D.ietf-pim-3228bis]. [RFC9778].
There are two IGMP message types of concern to the IGMPv3 protocol There are two IGMP message types of concern to the IGMPv3 protocol
described in this document: described in this document:
+===================+=============================+ +===================+=============================+
| Type Number (hex) | Message Name | | Type Number (hex) | Message Name |
+===================+=============================+ +===================+=============================+
| 0x11 | Membership Query | | 0x11 | Membership Query |
+-------------------+-----------------------------+ +-------------------+-----------------------------+
| 0x22 | Version 3 Membership Report | | 0x22 | Version 3 Membership Report |
+-------------------+-----------------------------+ +-------------------+-----------------------------+
Table 1: New messages introduced by IGMP3 Table 1: New Messages Introduced by IGMPv3
An implementation of IGMPv3 MUST also support the following three An implementation of IGMPv3 MUST also support the following three
message types, for interoperation with previous versions of IGMP (see message types, for interoperation with previous versions of IGMP (see
Section 7): Section 7):
+===================+=============================+===========+ +===================+=============================+===========+
| Type Number (hex) | Message Name | Reference | | Type Number (hex) | Message Name | Reference |
+===================+=============================+===========+ +===================+=============================+===========+
| 0x12 | Version 1 Membership Report | [RFC1112] | | 0x12 | Version 1 Membership Report | [RFC1112] |
+-------------------+-----------------------------+-----------+ +-------------------+-----------------------------+-----------+
| 0x16 | Version 2 Membership Report | [RFC2236] | | 0x16 | Version 2 Membership Report | [RFC2236] |
+-------------------+-----------------------------+-----------+ +-------------------+-----------------------------+-----------+
| 0x17 | Version 2 Leave Group | [RFC2236] | | 0x17 | Version 2 Leave Group | [RFC2236] |
+-------------------+-----------------------------+-----------+ +-------------------+-----------------------------+-----------+
Table 2: Legacy IGMP messages Table 2: Legacy IGMP Messages
Unrecognized message types MUST be silently ignored. Other message Unrecognized message types MUST be silently ignored. Other message
types may be used by newer versions or extensions of IGMP, by types may be used by newer versions or extensions of IGMP, by
multicast routing protocols, or for other uses. multicast routing protocols, or for other uses.
In this document, unless otherwise qualified, the capitalized words In this document, unless otherwise qualified, the capitalized words
"Query" and "Report" refer to IGMP Membership Queries and IGMP "Query" and "Report" refer to IGMP Membership Queries and IGMP
Version 3 Membership Reports, respectively. Version 3 Membership Reports, respectively.
4.1. Membership Query Message 4.1. Membership Query Message
skipping to change at page 12, line 8 skipping to change at line 517
. . . . . .
+- -+ +- -+
| Source Address [N] | | Source Address [N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IGMPv3 Query Message Figure 1: IGMPv3 Query Message
4.1.1. Max Resp Code 4.1.1. Max Resp Code
The Max Resp Code field specifies the maximum time allowed before The Max Resp Code field specifies the maximum time allowed before
sending a responding report. The actual time allowed, called the Max sending a responding report. The actual time allowed, called the
Resp Time, is represented in units of 1/10 second and is derived from "Max Resp Time", is represented in units of 1/10 second and is
the Max Resp Code as follows: derived from the Max Resp Code as follows:
If Max Resp Code < 128, Max Resp Time = Max Resp Code * If Max Resp Code < 128, Max Resp Time = Max Resp Code
If Max Resp Code >= 128, Max Resp Code represents a floating-point * If Max Resp Code >= 128, Max Resp Code represents a floating-point
value as follows: value as follows:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|1| exp | mant | |1| exp | mant |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Max Resp Time = (mant | 0x10) << (exp + 3) Max Resp Time = (mant | 0x10) << (exp + 3)
Figure 2: Max Resp Code Representation Figure 2: Max Resp Code Representation
Small values of Max Resp Time allow IGMPv3 routers to tune the "leave Small values of Max Resp Time allow IGMPv3 routers to tune the "leave
latency" (the time between the moment the last host leaves a group latency" (the time between the moment the last host leaves a group
and the moment the routing protocol is notified that there are no and the moment the routing protocol is notified that there are no
more members). Larger values, especially in the exponential range, more members). Larger values, especially in the exponential range,
allow tuning of the burstiness of IGMP traffic on a network. allow tuning of the burstiness of IGMP traffic on a network.
4.1.2. Checksum 4.1.2. Checksum
The Checksum is the 16-bit one's complement of the one's complement The Checksum field is the 16-bit one's complement of the one's
sum of the whole IGMP message (the entire IP payload). For computing complement sum of the whole IGMP message (the entire IP payload).
the checksum, the Checksum field is set to zero. When receiving For computing the checksum, the Checksum field is set to zero. When
packets, the checksum MUST be verified before processing a packet receiving packets, the checksum MUST be verified before processing a
[RFC1071]. packet [RFC1071].
4.1.3. Group Address 4.1.3. Group Address
The Group Address field is set to zero when sending a General Query, The Group Address field is set to zero when sending a General Query
and set to the IP multicast address being queried when sending a and set to the IP multicast address being queried when sending a
Group-Specific Query or Group-and-Source-Specific Query (see Group-Specific Query or Group-and-Source-Specific Query (see
Section 4.1.9, below). Section 4.1.9, below).
4.1.4. Flags 4.1.4. Flags
The Flags field is a bitstring managed by an IANA registry defined in The Flags field is a bitstring managed by the "IGMP Type Numbers"
[I-D.ietf-pim-3228bis]. registry defined in [RFC9778].
4.1.5. S Flag (Suppress Router-Side Processing) 4.1.5. S Flag (Suppress Router-Side Processing)
When set to one, the S Flag indicates to any receiving multicast When set to one, the S flag indicates to any receiving multicast
routers that they are to suppress the normal timer updates they routers that they are to suppress the normal timer updates they
perform upon hearing a Query. It does not, however, suppress the perform upon hearing a Query. It does not, however, suppress the
querier election or the normal "host-side" processing of a Query that querier election or the normal "host-side" processing of a Query that
a router may be required to perform as a consequence of itself being a router may be required to perform as a consequence of itself being
a group member. a group member.
4.1.6. QRV (Querier's Robustness Variable) 4.1.6. QRV (Querier's Robustness Variable)
If non-zero, the QRV field contains the [Robustness Variable] value If non-zero, the QRV field contains the [Robustness Variable] value
used by the querier, i.e., the sender of the Query. If the querier's used by the querier, i.e., the sender of the Query. If the querier's
[Robustness Variable] exceeds 7, the maximum value of the QRV field, [Robustness Variable] exceeds 7, the maximum value of the QRV field,
the QRV is set to zero. Routers adopt the QRV value from the most the QRV is set to zero. Routers adopt the QRV value from the most
recently received Query as their own [Robustness Variable] value, recently received Query as their own [Robustness Variable] value,
unless that most recently received QRV was zero, in which case the unless that most recently received QRV was zero, in which case the
receivers use the default [Robustness Variable] value specified in receivers use the default [Robustness Variable] value specified in
Section 8.1 or a statically configured value. Section 8.1 or a statically configured value.
4.1.7. QQIC (Querier's Query Interval Code) 4.1.7. QQIC (Querier's Query Interval Code)
The Querier's Query Interval Code field specifies the [Query The QQIC field specifies the [Query Interval] used by the querier.
Interval] used by the querier. The actual interval, called the The actual interval, called the "Querier's Query Interval (QQI)", is
Querier's Query Interval (QQI), is represented in units of seconds represented in units of seconds and is derived from the QQIC as
and is derived from the Querier's Query Interval Code as follows: follows:
If QQIC < 128, QQI = QQIC * If QQIC < 128, QQI = QQIC
If QQIC >= 128, QQIC represents a floating-point value as follows: * If QQIC >= 128, QQIC represents a floating-point value as follows:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|1| exp | mant | |1| exp | mant |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
QQI = (mant | 0x10) << (exp + 3) QQI = (mant | 0x10) << (exp + 3)
Figure 3: QQIC Representation Figure 3: QQIC Representation
Multicast routers that are not the current querier adopt the QQI Multicast routers that are not the current querier adopt the QQI
value from the most recently received Query as their own [Query value from the most recently received Query as their own [Query
Interval] value, unless that most recently received QQI was zero, in Interval] value, unless that most recently received QQI was zero, in
which case the receiving routers use the default [Query Interval] which case the receiving routers use the default [Query Interval]
value specified in Section 8.2. value specified in Section 8.2.
4.1.8. Number of Sources (N) 4.1.8. Number of Sources (N)
The Number of Sources (N) field specifies how many source addresses The Number of Sources (N) field specifies how many source addresses
are present in the Query. This number is zero in a General Query or are present in the Query. This number is zero in a General Query or
a Group-Specific Query, and non-zero in a Group-and-Source-Specific a Group-Specific Query and non-zero in a Group-and-Source-Specific
Query. This number is limited by the MTU of the network over which Query. This number is limited by the MTU of the network over which
the Query is transmitted. For example, on an Ethernet with an MTU of the Query is transmitted. For example, on an Ethernet with an MTU of
1500 octets, the IP header including the Router Alert option consumes 1500 octets, the IP header including the Router Alert option consumes
24 octets, and the IGMP fields up to including the Number of Sources 24 octets, and the IGMP fields up to and including the Number of
(N) field consume 12 octets, leaving 1464 octets for source Sources (N) field consume 12 octets, leaving 1464 octets for source
addresses, which limits the number of source addresses to 366 addresses, which limits the number of source addresses to 366
(1464/4). (1464/4).
4.1.9. Source Address [i] 4.1.9. Source Address [i]
The Source Address [i] fields are a vector of n IP unicast addresses, The Source Address [i] fields are a vector of n IP unicast addresses,
where n is the value in the Number of Sources (N) field. where n is the value in the Number of Sources (N) field.
4.1.10. Additional Data 4.1.10. Additional Data
If the Packet Length field in the IP header of a received Query If the Packet Length field in the IP header of a received Query
indicates that there are additional octets of data present, beyond indicates that there are additional octets of data present, beyond
the fields described here, IGMPv3 implementations MUST include those the fields described here, IGMPv3 implementations MUST include those
octets in the computation to verify the received IGMP Checksum, but octets in the computation to verify the received IGMP Checksum but
MUST otherwise ignore those additional octets. When sending a Query, MUST otherwise ignore those additional octets. When sending a Query,
an IGMPv3 implementation MUST NOT include additional octets beyond an IGMPv3 implementation MUST NOT include additional octets beyond
the fields described here. the fields described here.
4.1.11. Query Variants 4.1.11. Query Variants
There are three variants of the Query message: There are three variants of the Query message:
1. A General Query is sent by a multicast router to learn the 1. A General Query is sent by a multicast router to learn the
complete multicast reception state of the neighboring interfaces complete multicast reception state of the neighboring interfaces
skipping to change at page 17, line 31 skipping to change at line 736
. . . .
. Auxiliary Data . . Auxiliary Data .
. . . .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IGMPv3 Report Group Record Figure 5: IGMPv3 Report Group Record
4.2.1. Reserved 4.2.1. Reserved
The Reserved field is set to zero on transmission, and ignored on The Reserved field is set to zero on transmission and ignored on
reception. reception.
4.2.2. Checksum 4.2.2. Checksum
The Checksum is the 16-bit one's complement of the one's complement The Checksum field is the 16-bit one's complement of the one's
sum of the whole IGMP message (the entire IP payload). For computing complement sum of the whole IGMP message (the entire IP payload).
the checksum, the Checksum field is set to zero. When receiving For computing the checksum, the Checksum field is set to zero. When
packets, the checksum MUST be verified before processing a message. receiving packets, the checksum MUST be verified before processing a
message.
4.2.3. Flags 4.2.3. Flags
The Flags field is a bitstring managed by an IANA registry defined in The Flags field is a bitstring managed by the "IGMP Type Numbers"
[I-D.ietf-pim-3228bis]. registry defined in [RFC9778].
4.2.4. Number of Group Records (M) 4.2.4. Number of Group Records (M)
The Number of Group Records (M) field specifies how many Group The Number of Group Records (M) field specifies how many Group
Records are present in this Report. Records are present in this Report.
4.2.5. Group Record 4.2.5. Group Record
Each Group Record is a block of fields containing information Each Group Record is a block of fields containing information
pertaining to the sender's membership in a single multicast group on pertaining to the sender's membership in a single multicast group on
skipping to change at page 18, line 43 skipping to change at line 795
The Source Address [i] fields are a vector of n IP unicast addresses, The Source Address [i] fields are a vector of n IP unicast addresses,
where n is the value in this record's Number of Sources (N) field. where n is the value in this record's Number of Sources (N) field.
4.2.11. Auxiliary Data 4.2.11. Auxiliary Data
The Auxiliary Data field, if present, contains additional information The Auxiliary Data field, if present, contains additional information
pertaining to this Group Record. The protocol specified in this pertaining to this Group Record. The protocol specified in this
document, IGMPv3, does not define any auxiliary data. Therefore, document, IGMPv3, does not define any auxiliary data. Therefore,
implementations of IGMPv3 MUST NOT include any auxiliary data (i.e., implementations of IGMPv3 MUST NOT include any auxiliary data (i.e.,
MUST set the Aux Data Len field to zero) in any transmitted Group MUST set the Aux Data Len field to zero) in any transmitted Group
Record, and MUST ignore any auxiliary data present in any received Record and MUST ignore any auxiliary data present in any received
Group Record. The semantics and internal encoding of the Auxiliary Group Record. The semantics and internal encoding of the Auxiliary
Data field are to be defined by any future version or extension of Data field are to be defined by any future version or extension of
IGMP that uses this field. IGMP that uses this field.
4.2.12. Additional Data 4.2.12. Additional Data
If the Packet Length field in the IP header of a received Report If the Packet Length field in the IP header of a received Report
indicates that there are additional octets of data present, beyond indicates that there are additional octets of data present, beyond
the last Group Record, IGMPv3 implementations MUST include those the last Group Record, IGMPv3 implementations MUST include those
octets in the computation to verify the received IGMP Checksum, but octets in the computation to verify the received IGMP Checksum but
MUST otherwise ignore those additional octets. When sending a MUST otherwise ignore those additional octets. When sending a
Report, an IGMPv3 implementation MUST NOT include additional octets Report, an IGMPv3 implementation MUST NOT include additional octets
beyond the last Group Record. beyond the last Group Record.
4.2.13. Group Record Types 4.2.13. Group Record Types
There are a number of different types of Group Records that may be There are a number of different types of Group Records that may be
included in a Report message: included in a Report message:
* A Current-State Record is sent by a system in response to a Query * A Current-State Record is sent by a system in response to a Query
received on an interface. It reports the current reception state received on an interface. It reports the current reception state
of that interface, with respect to a single multicast address. of that interface, with respect to a single multicast address.
The Record Type of a Current-State Record may be one of the The Record Type of a Current-State Record may be one of the
following two values: following two values:
1 - MODE_IS_INCLUDE - indicates that the interface has a filter 1. MODE_IS_INCLUDE - indicates that the interface has a filter
mode of INCLUDE for the specified multicast address. The mode of INCLUDE for the specified multicast address. The
Source Address [i] fields in this Group Record contain the Source Address [i] fields in this Group Record contain the
interface's source list for the specified multicast address, interface's source list for the specified multicast address,
if it is non-empty. if it is non-empty.
2 - MODE_IS_EXCLUDE - indicates that the interface has a filter 2. MODE_IS_EXCLUDE - indicates that the interface has a filter
mode of EXCLUDE for the specified multicast address. The mode of EXCLUDE for the specified multicast address. The
Source Address [i] fields in this Group Record contain the Source Address [i] fields in this Group Record contain the
interface's source list for the specified multicast address, interface's source list for the specified multicast address,
if it is non-empty. An SSM-aware host SHOULD NOT send a if it is non-empty. An SSM-aware host SHOULD NOT send a
MODE_IS_EXCLUDE record type for multicast addresses that fall MODE_IS_EXCLUDE record type for multicast addresses that fall
within the SSM address range as they will be ignored by SSM- within the SSM address range as they will be ignored by SSM-
aware routers [RFC4604]. aware routers [RFC4604].
* A Filter-Mode-Change Record is sent by a system whenever a local * A Filter-Mode-Change Record is sent by a system whenever a local
invocation of IPMulticastListen causes a change of the filter mode invocation of IPMulticastListen causes a change of the filter mode
(i.e., a change from INCLUDE to EXCLUDE, or from EXCLUDE to (i.e., a change from INCLUDE to EXCLUDE, or from EXCLUDE to
INCLUDE), of the interface-level state entry for a particular INCLUDE) of the interface-level state entry for a particular
multicast address. The Record is included in a Report sent from multicast address. The Record is included in a Report sent from
the interface on which the change occurred. The Record Type of a the interface on which the change occurred. The Record Type of a
Filter-Mode-Change Record may be one of the following two values: Filter-Mode-Change Record may be one of the following two values:
3 - CHANGE_TO_INCLUDE_MODE - indicates that the interface has 3. CHANGE_TO_INCLUDE_MODE - indicates that the interface has
changed to INCLUDE filter mode for the specified multicast changed to INCLUDE filter mode for the specified multicast
address. The Source Address [i] fields in this Group Record address. The Source Address [i] fields in this Group Record
contain the interface's new source list for the specified contain the interface's new source list for the specified
multicast address, if it is non-empty. multicast address, if it is non-empty.
4 - CHANGE_TO_EXCLUDE_MODE - indicates that the interface has 4. CHANGE_TO_EXCLUDE_MODE - indicates that the interface has
changed to EXCLUDE filter mode for the specified multicast changed to EXCLUDE filter mode for the specified multicast
address. The Source Address [i] fields in this Group Record address. The Source Address [i] fields in this Group Record
contain the interface's new source list for the specified contain the interface's new source list for the specified
multicast address, if it is non-empty. An SSM-aware host multicast address, if it is non-empty. An SSM-aware host
SHOULD NOT send a CHANGE_TO_EXCLUDE_MODE record type for SHOULD NOT send a CHANGE_TO_EXCLUDE_MODE record type for
multicast addresses that fall within the SSM address range. multicast addresses that fall within the SSM address range.
* A Source-List-Change Record is sent by a system whenever a local * A Source-List-Change Record is sent by a system whenever a local
invocation of IPMulticastListen causes a change of source list invocation of IPMulticastListen causes a change of the source list
that is not coincident with a change of filter mode, of the that is not coincident with a change of the filter mode, of the
interface-level state entry for a particular multicast address. interface-level state entry for a particular multicast address.
The Record is included in a Report sent from the interface on The Record is included in a Report sent from the interface on
which the change occurred. The Record Type of a Source-List- which the change occurred. The Record Type of a Source-List-
Change Record may be one of the following two values: Change Record may be one of the following two values:
5 - ALLOW_NEW_SOURCES - indicates that the Source Address [i] 5. ALLOW_NEW_SOURCES - indicates that the Source Address [i]
fields in this Group Record contain a list of the additional fields in this Group Record contain a list of the additional
sources that the system wishes to hear from, for packets sent sources that the system wishes to hear from, for packets sent
to the specified multicast address. If the change was to an to the specified multicast address. If the change was to an
INCLUDE source list, these are the addresses that were added INCLUDE source list, these are the addresses that were added
to the list; if the change was to an EXCLUDE source list, to the list; if the change was to an EXCLUDE source list,
these are the addresses that were deleted from the list. these are the addresses that were deleted from the list.
6 - BLOCK_OLD_SOURCES - indicates that the Source Address [i] 6. BLOCK_OLD_SOURCES - indicates that the Source Address [i]
fields in this Group Record contain a list of the sources fields in this Group Record contain a list of the sources that
that the system no longer wishes to hear from, for packets the system no longer wishes to hear from, for packets sent to
sent to the specified multicast address. If the change was the specified multicast address. If the change was to an
to an INCLUDE source list, these are the addresses that were INCLUDE source list, these are the addresses that were deleted
deleted from the list; if the change was to an EXCLUDE source from the list; if the change was to an EXCLUDE source list,
list, these are the addresses that were added to the list. these are the addresses that were added to the list.
If a change of source list results in both allowing new sources and If a change of source list results in both allowing new sources and
blocking old sources, then two Group Records are sent for the same blocking old sources, then two Group Records are sent for the same
multicast address, one of type ALLOW_NEW_SOURCES and one of type multicast address, one of type ALLOW_NEW_SOURCES and one of type
BLOCK_OLD_SOURCES. BLOCK_OLD_SOURCES.
We use the term State-Change Record to refer to either a Filter- We use the term "State-Change Record" to refer to either a Filter-
Mode-Change Record or a Source-List-Change Record. Mode-Change Record or a Source-List-Change Record.
Unrecognized Record Type values MUST be silently ignored. Unrecognized Record Type values MUST be silently ignored.
4.2.14. IP Source Addresses for Reports 4.2.14. IP Source Addresses for Reports
An IGMP report is sent with a valid unicast IPv4 source address for An IGMP report is sent with a valid unicast IPv4 source address for
the destination subnet. The 0.0.0.0 source address may be used by a the destination subnet. The 0.0.0.0 source address may be used by a
system that has not yet acquired an IP address. Note that the system that has not yet acquired an IP address. Note that the
0.0.0.0 source address may simultaneously be used by multiple systems 0.0.0.0 source address may simultaneously be used by multiple systems
skipping to change at page 21, line 42 skipping to change at line 929
IS_IN ( x ) - Type MODE_IS_INCLUDE, source addresses x IS_IN ( x ) - Type MODE_IS_INCLUDE, source addresses x
IS_EX ( x ) - Type MODE_IS_EXCLUDE, source addresses x IS_EX ( x ) - Type MODE_IS_EXCLUDE, source addresses x
TO_IN ( x ) - Type CHANGE_TO_INCLUDE_MODE, source addresses x TO_IN ( x ) - Type CHANGE_TO_INCLUDE_MODE, source addresses x
TO_EX ( x ) - Type CHANGE_TO_EXCLUDE_MODE, source addresses x TO_EX ( x ) - Type CHANGE_TO_EXCLUDE_MODE, source addresses x
ALLOW ( x ) - Type ALLOW_NEW_SOURCES, source addresses x ALLOW ( x ) - Type ALLOW_NEW_SOURCES, source addresses x
BLOCK ( x ) - Type BLOCK_OLD_SOURCES, source addresses x BLOCK ( x ) - Type BLOCK_OLD_SOURCES, source addresses x
where x is either: where x is either:
* a capital letter (e.g., "A") to represent the set of source * a capital letter (e.g., "A") to represent the set of source
addresses, or addresses or
* a set expression (e.g., "A+B"), where "A+B" means the union of * a set expression (e.g., "A+B"), where "A+B" means the union of
sets A and B, "A*B" means the intersection of sets A and B, and sets A and B, "A*B" means the intersection of sets A and B, and
"A-B" means the removal of all elements of set B from set A. "A-B" means the removal of all elements of set B from set A.
4.2.17. Membership Report Size 4.2.17. Membership Report Size
If the set of Group Records required in a Report does not fit within If the set of Group Records required in a Report does not fit within
the size limit of a single Report message (as determined by the MTU the size limit of a single Report message (as determined by the MTU
of the network on which it will be sent), the Group Records are sent of the network on which it will be sent), the Group Records are sent
in as many Report messages as needed to report the entire set. in as many Report messages as needed to report the entire set.
If a single Group Record contains so many source addresses that it If a single Group Record contains so many source addresses that it
does not fit within the size limit of a single Report message, if its does not fit within the size limit of a single Report message, and if
Type is not MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE, it is split its Type is not MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE, it is
into multiple Group Records, each containing a different subset of split into multiple Group Records, each containing a different subset
the source addresses and each sent in a separate Report message. If of the source addresses and each sent in a separate Report message.
its Type is MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE, a single Group If its Type is MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE, a single
Record is sent, containing as many source addresses as can fit, and Group Record is sent, containing as many source addresses as can fit,
and the remaining source addresses are not reported; though the
the remaining source addresses are not reported; though the choice of choice of which sources to report is arbitrary, it is preferable to
which sources to report is arbitrary, it is preferable to report the report the same set of sources in each subsequent report, rather than
same set of sources in each subsequent report, rather than reporting reporting different sources each time.
different sources each time.
5. Description of the Protocol for Group Members 5. Description of the Protocol for Group Members
IGMP is an asymmetric protocol, specifying separate behaviors for IGMP is an asymmetric protocol, specifying separate behaviors for
group members -- that is, hosts or routers that wish to receive group members -- that is, hosts or routers that wish to receive
multicast packets -- and multicast routers. This section describes multicast packets -- and multicast routers. This section describes
the part of IGMPv3 that applies to all group members. (Note that a the part of IGMPv3 that applies to all group members. (Note that a
multicast router that is also a group member performs both parts of multicast router that is also a group member performs both parts of
IGMPv3, receiving and responding to its own IGMP message IGMPv3, receiving and responding to its own IGMP message
transmissions as well as those of its neighbors. The multicast transmissions as well as those of its neighbors. The multicast
skipping to change at page 23, line 6 skipping to change at line 978
For interoperability with multicast routers running older versions of For interoperability with multicast routers running older versions of
IGMP, systems maintain a MulticastRouterVersion variable for each IGMP, systems maintain a MulticastRouterVersion variable for each
interface on which multicast reception is supported. This section interface on which multicast reception is supported. This section
describes the behavior of group member systems on interfaces for describes the behavior of group member systems on interfaces for
which MulticastRouterVersion = 3. The algorithm for determining which MulticastRouterVersion = 3. The algorithm for determining
MulticastRouterVersion, and the behavior for versions other than 3, MulticastRouterVersion, and the behavior for versions other than 3,
are described in Section 7. are described in Section 7.
The all-systems multicast address, 224.0.0.1, is handled as a special The all-systems multicast address, 224.0.0.1, is handled as a special
case. On all systems -- that is all hosts and routers, including case. On all systems -- that is, all hosts and routers including
multicast routers -- reception of packets destined to the all-systems multicast routers -- reception of packets destined to the all-systems
multicast address, from all sources, is permanently enabled on all multicast address, from all sources, is permanently enabled on all
interfaces on which multicast reception is supported. No IGMP interfaces on which multicast reception is supported. No IGMP
messages are ever sent regarding the all-systems multicast address. messages are ever sent regarding the all-systems multicast address.
There are two types of events that trigger IGMPv3 protocol actions on There are two types of events that trigger IGMPv3 protocol actions on
an interface: an interface:
* a change of the interface reception state, caused by a local * A change of the interface reception state, caused by a local
invocation of IPMulticastListen. invocation of IPMulticastListen.
* reception of a Query. * The reception of a Query.
(Received IGMP messages of types other than Query are silently (Received IGMP messages of types other than Query are silently
ignored, except as required for interoperation with earlier versions ignored, except as required for interoperation with earlier versions
of IGMP.) of IGMP.)
The following subsections describe the actions to be taken for each The following subsections describe the actions to be taken for each
of these two cases. In those descriptions, timer and counter names of these two cases. In those descriptions, timer and counter names
appear in square brackets. The default values for those timers and appear in square brackets. The default values for those timers and
counters are specified in Section 8. counters are specified in Section 8.
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An invocation of IPMulticastListen may cause the multicast reception An invocation of IPMulticastListen may cause the multicast reception
state of an interface to change, according to the rules in state of an interface to change, according to the rules in
Section 3.2. Each such change affects the per-interface entry for a Section 3.2. Each such change affects the per-interface entry for a
single multicast address. single multicast address.
A change of interface state causes the system to immediately transmit A change of interface state causes the system to immediately transmit
a State-Change Report from that interface. The type and contents of a State-Change Report from that interface. The type and contents of
the Group Record(s) in that Report are determined by comparing the the Group Record(s) in that Report are determined by comparing the
filter mode and source list for the affected multicast address before filter mode and source list for the affected multicast address before
and after the change, according to the table below. If no interface and after the change, according to Table 3. If no interface state
state existed for that multicast address before the change (i.e., the existed for that multicast address before the change (i.e., the
change consisted of creating a new per-interface record), or if no change consisted of creating a new per-interface record), or if no
state exists after the change (i.e., the change consisted of deleting state exists after the change (i.e., the change consisted of deleting
a per-interface record), then the "non-existent" state is considered a per-interface record), then the "non-existent" state is considered
to have a filter mode of INCLUDE and an empty source list. to have a filter mode of INCLUDE and an empty source list.
+=============+=============+==========================+ +=============+=============+==========================+
| Old State | New State | State-Change Record Sent | | Old State | New State | State-Change Record Sent |
+=============+=============+==========================+ +=============+=============+==========================+
| INCLUDE (A) | INCLUDE (B) | ALLOW (B-A), BLOCK (A-B) | | INCLUDE (A) | INCLUDE (B) | ALLOW (B-A), BLOCK (A-B) |
+-------------+-------------+--------------------------+ +-------------+-------------+--------------------------+
| EXCLUDE (A) | EXCLUDE (B) | ALLOW (A-B), BLOCK (B-A) | | EXCLUDE (A) | EXCLUDE (B) | ALLOW (A-B), BLOCK (B-A) |
+-------------+-------------+--------------------------+ +-------------+-------------+--------------------------+
| INCLUDE (A) | EXCLUDE (B) | TO_EX (B) | | INCLUDE (A) | EXCLUDE (B) | TO_EX (B) |
+-------------+-------------+--------------------------+ +-------------+-------------+--------------------------+
| EXCLUDE (A) | INCLUDE (B) | TO_IN (B) | | EXCLUDE (A) | INCLUDE (B) | TO_IN (B) |
+-------------+-------------+--------------------------+ +-------------+-------------+--------------------------+
Table 3 Table 3
If the computed source list for either an ALLOW or a BLOCK State- If the computed source list for either an ALLOW or a BLOCK State-
Change Record is empty, that record is omitted from the Report Change Record is empty, that record is omitted from the Report
message. message.
To cover the possibility of the State-Change Report being missed by To cover the possibility of the State-Change Report being missed by
one or more multicast routers, it is retransmitted [Robustness one or more multicast routers, it is retransmitted [Robustness
skipping to change at page 24, line 36 skipping to change at line 1050
range (0, [Unsolicited Report Interval]). range (0, [Unsolicited Report Interval]).
If more changes to the same interface state entry occur before all If more changes to the same interface state entry occur before all
the retransmissions of the State-Change Report for the first change the retransmissions of the State-Change Report for the first change
have been completed, each such additional change triggers the have been completed, each such additional change triggers the
immediate transmission of a new State-Change Report. immediate transmission of a new State-Change Report.
The contents of the new transmitted report are calculated as follows. The contents of the new transmitted report are calculated as follows.
As was done with the first report, the interface state for the As was done with the first report, the interface state for the
affected group before and after the latest change is compared. The affected group before and after the latest change is compared. The
report records expressing the difference are built according to the report records expressing the difference are built according to
table above. However these records are not transmitted in a message Table 3. However, these records are not transmitted in a message but
but instead merged with the contents of the pending report, to create instead are merged with the contents of the pending report to create
the new State-Change report. The rules for merging the difference the new State-Change report. The rules for merging the difference
report resulting from the state change and the pending report are report resulting from the state change and the pending report are
described below. described below.
The transmission of the merged State-Change Report terminates The transmission of the merged State-Change Report terminates
retransmissions of the earlier State-Change Reports for the same retransmissions of the earlier State-Change Reports for the same
multicast address, and becomes the first of [Robustness Variable] multicast address, and becomes the first of [Robustness Variable]
transmissions of State-Change Reports. transmissions of State-Change Reports.
Each time a source is included in the difference report calculated Each time a source is included in the difference report calculated
above, retransmission state for that source needs to be maintained above, retransmission state for that source needs to be maintained
until [Robustness Variable] State-Change reports have been sent by until [Robustness Variable] State-Change reports have been sent by
the host. This is done in order to ensure that a series of the host. This is done in order to ensure that a series of
successive state changes do not break the protocol robustness. successive state changes do not break the protocol robustness.
If the interface reception-state change that triggers the new report If the interface reception-state change that triggers the new report
is a filter-mode change, then the next [Robustness Variable] State- is a filter-mode change, then the next [Robustness Variable] State-
Change Reports will include a Filter-Mode-Change record. This Change Reports will include a Filter-Mode-Change Record. This
applies even if any number of source-list changes occur in that applies even if any number of source-list changes occur in that
period. The host has to maintain retransmission state for the group period. The host has to maintain retransmission state for the group
until the [Robustness Variable] State-Change reports have been sent. until the [Robustness Variable] State-Change reports have been sent.
When [Robustness Variable] State-Change reports with Filter-Mode- When [Robustness Variable] State-Change reports with Filter-Mode-
Change records have been transmitted after the last filter-mode Change Records have been transmitted after the last filter-mode
change, and if source-list changes to the interface reception have change, and if source-list changes to the interface reception have
scheduled additional reports, then the next State-Change report will scheduled additional reports, then the next State-Change report will
include Source-List-Change records. include Source-List-Change Records.
Each time a State-Change Report is transmitted, the contents are Each time a State-Change Report is transmitted, the contents are
determined as follows. If the report should contain a Filter-Mode- determined as follows. If the report should contain a Filter-Mode-
Change record, then if the current filter-mode of the interface is Change Record, and if the current filter-mode of the interface is
INCLUDE, a TO_IN record is included in the report, otherwise a TO_EX INCLUDE, a TO_IN record is included in the report; otherwise, a TO_EX
record is included. If instead the report should contain Source- record is included. If instead the report should contain Source-
List-Change records, an ALLOW and a BLOCK record are included. The List-Change Records, an ALLOW and a BLOCK record are included. The
contents of these records are built according to the table below. contents of these records are built according to Table 4.
+========+==============================+ +========+==============================+
| Record | Sources Included | | Record | Sources Included |
+========+==============================+ +========+==============================+
| TO_IN | All in the current interface | | TO_IN | All in the current interface |
| | state that must be forwarded | | | state that must be forwarded |
+--------+------------------------------+ +--------+------------------------------+
| TO_EX | All in the current interface | | TO_EX | All in the current interface |
| | state that must be blocked | | | state that must be blocked |
+--------+------------------------------+ +--------+------------------------------+
| ALLOW | All with retransmission | | ALLOW | All with retransmission |
| | state that must be forwarded | | | state that must be forwarded |
+--------+------------------------------+ +--------+------------------------------+
| BLOCK | All with retransmission | | BLOCK | All with retransmission |
| | state that must be blocked | | | state that must be blocked |
+--------+------------------------------+ +--------+------------------------------+
Table 4 Table 4
If the computed source list for either an ALLOW or a BLOCK record is If the computed source list for either an ALLOW or a BLOCK record is
empty, that record is omitted from the State-Change report. empty, that record is omitted from the State-Change report.
Note: When the first State-Change report is sent, the non-existent Note: When the first State-Change report is sent, the non-existent
pending report to merge with, can be treated as a source-change pending report to merge with can be treated as a source-change report
report with empty ALLOW and BLOCK records (no sources have with empty ALLOW and BLOCK records (no sources have retransmission
retransmission state). state).
5.2. Action on Reception of a Query 5.2. Action on Reception of a Query
When a system receives a Query, it does not respond immediately. When a system receives a Query, it does not respond immediately.
Instead, it delays its response by a random amount of time, bounded Instead, it delays its response by a random amount of time, bounded
by the Max Resp Time value derived from the Max Resp Code in the by the Max Resp Time value derived from the Max Resp Code in the
received Query message. A system may receive a variety of Queries on received Query message. A system may receive a variety of Queries on
different interfaces and of different kinds (e.g., General Queries, different interfaces and of different kinds (e.g., General Queries,
Group-Specific Queries, and Group-and-Source-Specific Queries), each Group-Specific Queries, and Group-and-Source-Specific Queries), each
of which may require its own delayed response. of which may require its own delayed response.
Before scheduling a response to a Query, the system must first Before scheduling a response to a Query, the system must first
consider previously scheduled pending responses and in many cases consider previously scheduled pending responses as, in many cases, it
schedule a combined response. Therefore, the system must be able to can schedule a combined response. Therefore, the system must be able
maintain the following state: to maintain the following state:
* A timer per interface for scheduling responses to General Queries. * A timer per interface for scheduling responses to General Queries.
* A per-group and interface timer for scheduling responses to Group- * A per-group and interface timer for scheduling responses to Group-
Specific and Group-and-Source-Specific Queries. Specific and Group-and-Source-Specific Queries.
* A per-group and interface list of sources to be reported in the * A per-group and interface list of sources to be reported in the
response to a Group-and-Source-Specific Query. response to a Group-and-Source-Specific Query.
When a new Query with the Router-Alert option arrives on an When a new Query with the Router Alert option arrives on an
interface, provided the system has state to report, a delay for a interface, provided the system has state to report, a delay for a
response is randomly selected in the range (0, [Max Resp Time]) where response is randomly selected in the range (0, [Max Resp Time]) where
Max Resp Time is derived from Max Resp Code in the received Query Max Resp Time is derived from Max Resp Code in the received Query
message. The following rules are then used to determine if a Report message. The following rules are then used to determine if a Report
needs to be scheduled and the type of Report to schedule. The rules needs to be scheduled and the type of Report to schedule. The rules
are considered in order and only the first matching rule is applied. are considered in order and only the first matching rule is applied.
1. If there is a pending response to a previous General Query 1. If there is a pending response to a previous General Query
scheduled sooner than the selected delay, no additional response scheduled sooner than the selected delay, no additional response
needs to be scheduled. needs to be scheduled.
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When the timer in a pending response record expires, the system When the timer in a pending response record expires, the system
transmits, on the associated interface, one or more Report messages transmits, on the associated interface, one or more Report messages
carrying one or more Current-State Records (see Section 4.2.13), as carrying one or more Current-State Records (see Section 4.2.13), as
follows: follows:
1. If the expired timer is the interface timer (i.e., it is a 1. If the expired timer is the interface timer (i.e., it is a
pending response to a General Query), then one Current-State pending response to a General Query), then one Current-State
Record is sent for each multicast address for which the specified Record is sent for each multicast address for which the specified
interface has reception state, as described in Section 3.2. The interface has reception state, as described in Section 3.2. The
Current- State Record carries the multicast address and its Current-State Record carries the multicast address and its
associated filter mode (MODE_IS_INCLUDE or MODE_IS_EXCLUDE) and associated filter mode (MODE_IS_INCLUDE or MODE_IS_EXCLUDE) and
source list. Multiple Current-State Records are packed into source list. Multiple Current-State Records are packed into
individual Report messages, to the extent possible. individual Report messages, to the extent possible.
This naive algorithm may result in bursts of packets when a This naive algorithm may result in bursts of packets when a
system is a member of a large number of groups. Instead of using system is a member of a large number of groups. Instead of using
a single interface timer, implementations are recommended to a single interface timer, implementations are recommended to
spread transmission of such Report messages over the interval (0, spread transmission of such Report messages over the interval (0,
[Max Resp Time]). Note that any such implementation MUST avoid [Max Resp Time]). Note that any such implementation MUST avoid
the "ack-implosion" problem, i.e., MUST NOT send a Report the "ack-implosion" problem, i.e., MUST NOT send a Report
immediately on reception of a General Query. immediately on reception of a General Query.
2. If the expired timer is a group timer and the list of recorded 2. If the expired timer is a group timer and the list of recorded
sources for the that group is empty (i.e., it is a pending sources for that group is empty (i.e., it is a pending response
response to a Group-Specific Query), then if and only if the to a Group-Specific Query), then if and only if the interface has
interface has reception state for that group address, a single reception state for that group address, a single Current-State
Current-State Record is sent for that address. The Current-State Record is sent for that address. The Current-State Record
Record carries the multicast address and its associated filter carries the multicast address and its associated filter mode
mode (MODE_IS_INCLUDE or MODE_IS_EXCLUDE) and source list. (MODE_IS_INCLUDE or MODE_IS_EXCLUDE) and source list.
3. If the expired timer is a group timer and the list of recorded 3. If the expired timer is a group timer and the list of recorded
sources for that group is non-empty (i.e., it is a pending sources for that group is non-empty (i.e., it is a pending
response to a Group-and-Source-Specific Query), then if and only response to a Group-and-Source-Specific Query), then if and only
if the interface has reception state for that group address, the if the interface has reception state for that group address, the
contents of the responding Current-State Record is determined contents of the responding Current-State Record is determined
from the interface state and the pending response record, as from the interface state and the pending response record, as
specified in the following table: specified in Table 5.
+=====================+=========================+===============+ +=====================+=========================+===============+
| Per-Interface State | Set of Sources in the | Current-State | | Per-Interface State | Set of Sources in the | Current-State |
| | Pending Response Record | Record | | | Pending Response Record | Record |
+=====================+=========================+===============+ +=====================+=========================+===============+
| INCLUDE (A) | B | IS_IN (A*B) | | INCLUDE (A) | B | IS_IN (A*B) |
+---------------------+-------------------------+---------------+ +---------------------+-------------------------+---------------+
| EXCLUDE (A) | B | IS_IN (B-A) | | EXCLUDE (A) | B | IS_IN (B-A) |
+---------------------+-------------------------+---------------+ +---------------------+-------------------------+---------------+
Table 5 Table 5
If the resulting Current-State Record has an empty set of source If the resulting Current-State Record has an empty set of source
addresses, then no response is sent. addresses, then no response is sent.
Finally, after any required Report messages have been generated, the Finally, after any required Report messages have been generated, the
source lists associated with any reported groups are cleared. source lists associated with any reported groups are cleared.
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3 adds the capability for a multicast router to also learn which 3 adds the capability for a multicast router to also learn which
sources are of interest to neighboring systems, for packets sent to sources are of interest to neighboring systems, for packets sent to
any particular multicast address. The information gathered by IGMP any particular multicast address. The information gathered by IGMP
is provided to whichever multicast routing protocol is being used by is provided to whichever multicast routing protocol is being used by
the router, in order to ensure that multicast packets are delivered the router, in order to ensure that multicast packets are delivered
to all networks where there are interested receivers. to all networks where there are interested receivers.
This section describes the part of IGMPv3 that is performed by This section describes the part of IGMPv3 that is performed by
multicast routers. Multicast routers may also themselves become multicast routers. Multicast routers may also themselves become
members of multicast groups, and therefore also perform the group members of multicast groups, and therefore also perform the group
member part of IGMPv3, described in Section 5. member part of IGMPv3, as described in Section 5.
A multicast router performs the protocol described in this section A multicast router performs the protocol described in this section
over each of its directly-attached networks. If a multicast router over each of its directly attached networks. If a multicast router
has more than one interface to the same network, it only needs to has more than one interface to the same network, it only needs to
operate this protocol over one of those interfaces. On each operate this protocol over one of those interfaces. On each
interface over which this protocol is being run, the router MUST interface over which this protocol is being run, the router MUST
enable reception of multicast address 224.0.0.22, from all sources enable reception of multicast address 224.0.0.22 from all sources
(and MUST perform the group member part of IGMPv3 for that address on (and MUST perform the group member part of IGMPv3 for that address on
that interface). that interface).
Multicast routers need to know only that at least one system on an Multicast routers need to know only that at least one system on an
attached network is interested in packets to a particular multicast attached network is interested in packets to a particular multicast
address from a particular source; a multicast router is not required address from a particular source; a multicast router is not required
to keep track of the interests of each individual neighboring system. to keep track of the interests of each individual neighboring system.
(However, see Appendix A.2 point 1 for discussion.) (However, see Appendix A.2, item 1 for discussion.)
IGMPv3 is backward compatible with previous versions of the IGMP IGMPv3 is backward compatible with previous versions of the IGMP
protocol. In order to remain backward compatible with older IGMP protocol. In order to remain backward compatible with older IGMP
systems, IGMPv3 multicast routers MUST also implement versions 1 and systems, IGMPv3 multicast routers MUST also implement versions 1 and
2 of the protocol (see Section 7). 2 of the protocol (see Section 7).
6.1. Conditions for IGMP Queries 6.1. Conditions for IGMP Queries
Multicast routers send General Queries periodically to request group Multicast routers send General Queries periodically to request group
membership information from an attached network. These queries are membership information from an attached network. These queries are
skipping to change at page 30, line 6 skipping to change at line 1298
To enable all systems on a network to respond to changes in group To enable all systems on a network to respond to changes in group
membership, multicast routers send specific queries. A Group- membership, multicast routers send specific queries. A Group-
Specific Query is sent to verify there are no systems that desire Specific Query is sent to verify there are no systems that desire
reception of the specified group or to "rebuild" the desired reception of the specified group or to "rebuild" the desired
reception state for a particular group. Group-Specific Queries are reception state for a particular group. Group-Specific Queries are
sent when a router receives a State-Change record indicating a system sent when a router receives a State-Change record indicating a system
is leaving a group. is leaving a group.
A Group-and-Source Specific Query is used to verify there are no A Group-and-Source Specific Query is used to verify there are no
systems on a network which desire to receive traffic from a set of systems on a network that desire receiving traffic from a set of
sources. Group-and-Source Specific Queries list sources for a sources. Group-and-Source Specific Queries list sources for a
particular group which have been requested to no longer be forwarded. particular group that have been requested to no longer be forwarded.
This query is sent by a multicast router to learn if any systems This query is sent by a multicast router to learn if any systems
desire reception of packets to the specified group address from the desire reception of packets to the specified group address from the
specified source addresses. Group-and-Source Specific Queries are specified source addresses. Group-and-Source Specific Queries are
only sent in response to State-Change Records and never in response only sent in response to State-Change Records and never in response
to Current-State Records. Section 4.1.11 describes each query in to Current-State Records. Section 4.1.11 describes each query in
more detail. more detail.
6.2. IGMP State Maintained by Multicast Routers 6.2. IGMP State Maintained by Multicast Routers
Multicast routers implementing IGMPv3 keep state per group per Multicast routers implementing IGMPv3 keep state per group per
skipping to change at page 30, line 34 skipping to change at line 1326
(multicast address, group timer, filter-mode, (source records)) (multicast address, group timer, filter-mode, (source records))
Each source record is of the form: Each source record is of the form:
(source address, source timer) (source address, source timer)
If all sources within a given group are desired, an empty source If all sources within a given group are desired, an empty source
record list is kept with filter-mode set to EXCLUDE. This means record list is kept with filter-mode set to EXCLUDE. This means
hosts on this network want all sources for this group to be hosts on this network want all sources for this group to be
forwarded. This is the IGMPv3 equivalent to a IGMPv1 or IGMPv2 group forwarded. This is the IGMPv3 equivalent to an IGMPv1 or IGMPv2
join. group join.
6.2.1. Definition of Router Filter-Mode 6.2.1. Definition of Router Filter-Mode
To reduce internal state, IGMPv3 routers keep a filter-mode per group To reduce internal state, IGMPv3 routers keep a filter-mode per group
per attached network. This filter-mode is used to condense the total per attached network. This filter-mode is used to condense the total
desired reception state of a group to a minimum set such that all desired reception state of a group to a minimum set such that all
systems' memberships are satisfied. This filter-mode may change in systems' memberships are satisfied. This filter-mode may change in
response to the reception of particular types of group records or response to the reception of particular types of group records or
when certain timer conditions occur. In the following sections, we when certain timer conditions occur. In the following sections, we
use the term "router filter-mode" to refer to the filter-mode of a use the term "router filter-mode" to refer to the filter-mode of a
particular group within a router. Section 6.4 describes the changes particular group within a router. Section 6.4 describes the changes
of a router filter-mode per group record received. of a router filter-mode per group record received.
Conceptually, when a group record is received, the router filter-mode Conceptually, when a group record is received, the router filter-mode
for that group is updated to cover all the requested sources using for that group is updated to cover all the requested sources using
the least amount of state. As a rule, once a group record with a the least amount of state. As a rule, once a group record with a
filter-mode of EXCLUDE is received, the router filter-mode for that filter-mode of EXCLUDE is received, the router filter-mode for that
group will be EXCLUDE. group will be EXCLUDE.
When a router filter-mode for a group is EXCLUDE, the source record When a router filter-mode for a group is EXCLUDE, the source record
list contains two types of sources. The first type is the set which list contains two types of sources. The first type is the set that
represents conflicts in the desired reception state; this set must be represents conflicts in the desired reception state; this set must be
forwarded by some router on the network. The second type is the set forwarded by some router on the network. The second type is the set
of sources which hosts have requested to not be forwarded. of sources that hosts have requested to not be forwarded. Appendix A
Appendix A describes the reasons for keeping two different sets when describes the reasons for keeping two different sets when in EXCLUDE
in EXCLUDE mode. mode.
When a router filter-mode for a group is INCLUDE, the source record When a router filter-mode for a group is INCLUDE, the source record
list is the list of sources desired for the group. This is the total list is the list of sources desired for the group. This is the total
desired set of sources for that group. Each source in the source desired set of sources for that group. Each source in the source
record list must be forwarded by some router on the network. record list must be forwarded by some router on the network.
Because a reported group record with a filter-mode of EXCLUDE will Because a reported group record with a filter-mode of EXCLUDE will
cause a router to transition its filter-mode for that group to cause a router to transition its filter-mode for that group to
EXCLUDE, a mechanism for transitioning a router's filter-mode back to EXCLUDE, a mechanism for transitioning a router's filter-mode back to
INCLUDE must exist. If all systems with a group record in EXCLUDE INCLUDE must exist. If all systems with a group record in EXCLUDE
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timer with a lower bound of zero kept per group per attached network. timer with a lower bound of zero kept per group per attached network.
Group timers are updated according to the types of group records Group timers are updated according to the types of group records
received. received.
A group timer expiring when a router filter-mode for the group is A group timer expiring when a router filter-mode for the group is
EXCLUDE means there are no listeners on the attached network in EXCLUDE means there are no listeners on the attached network in
EXCLUDE mode. At this point, a router will transition to INCLUDE EXCLUDE mode. At this point, a router will transition to INCLUDE
filter-mode. Section 6.5 describes the actions taken when a group filter-mode. Section 6.5 describes the actions taken when a group
timer expires while in EXCLUDE mode. timer expires while in EXCLUDE mode.
The following table summarizes the role of the group timer. Table 6 summarizes the role of the group timer. Section 6.4
Section 6.4 describes the details of setting the group timer per type describes the details of setting the group timer per type of group
of group record received. record received.
+=============+=======+========================================+ +=============+=======+=========================================+
| Group | Group | Actions/Comments | | Group | Group | Actions/Comments |
| Filter-Mode | Timer | | | Filter-Mode | Timer | |
| | Value | | | | Value | |
+=============+=======+========================================+ +=============+=======+=========================================+
| INCLUDE | Timer | All members in INCLUDE mode. | | INCLUDE | Timer | All members in INCLUDE mode. |
| | >= 0 | | | | >= 0 | |
+-------------+-------+----------------------------------------+ +-------------+-------+-----------------------------------------+
| EXCLUDE | Timer | At least one member in EXCLUDE mode. | | EXCLUDE | Timer | At least one member in EXCLUDE mode. |
| | > 0 | | | | > 0 | |
+-------------+-------+----------------------------------------+ +-------------+-------+-----------------------------------------+
| EXCLUDE | Timer | No more listeners to group. If all | | EXCLUDE | Timer | No more listeners to group. If all |
| | == 0 | source timers have expired then delete | | | == 0 | source timers have expired, then delete |
| | | Group Record. If there are still | | | | Group Record. If there are still |
| | | source record timers running, switch | | | | source record timers running, switch to |
| | | to INCLUDE filter-mode using those | | | | INCLUDE filter-mode using those source |
| | | source records with running timers as | | | | records with running timers as the |
| | | the INCLUDE source record state. | | | | INCLUDE source record state. |
+-------------+-------+----------------------------------------+ +-------------+-------+-----------------------------------------+
Table 6 Table 6
6.2.3. Definition of Source Timers 6.2.3. Definition of Source Timers
A source timer is kept per source record and is a decrementing timer A source timer is kept per source record and is a decrementing timer
with a lower bound of zero. Source timers are updated according to with a lower bound of zero. Source timers are updated according to
the type and filter-mode of the group record received. Source timers the type and filter-mode of the group record received. Source timers
are always updated (for a particular group) whenever the source is are always updated (for a particular group) whenever the source is
present in a received record for that group. Section 6.4 describes present in a received record for that group. Section 6.4 describes
the setting of source timers per type of group records received. the setting of source timers per type of group records received.
A source record with a running timer with a router filter-mode for A source record with a running timer with a router filter-mode for
the group of INCLUDE means that there is currently one or more the group of INCLUDE means that there is currently one or more
systems (in INCLUDE filter-mode) which desire to receive that source. systems (in INCLUDE filter-mode) that desire to receive that source.
If a source timer expires with a router filter-mode for the group of If a source timer expires with a router filter-mode for the group of
INCLUDE, the router concludes that traffic from this particular INCLUDE, the router concludes that traffic from this particular
source is no longer desired on the attached network, and deletes the source is no longer desired on the attached network and deletes the
associated source record. associated source record.
Source timers are treated differently when a router filter-mode for a Source timers are treated differently when a router filter-mode for a
group is EXCLUDE. If a source record has a running timer with a group is EXCLUDE. If a source record has a running timer with a
router filter-mode for the group of EXCLUDE, it means that at least router filter-mode for the group of EXCLUDE, it means that at least
one system desires the source. It should therefore be forwarded by a one system desires the source. It should therefore be forwarded by a
router on the network. Appendix A describes the reasons for keeping router on the network. Appendix A describes the reasons for keeping
state for sources that have been requested to be forwarded while in state for sources that have been requested to be forwarded while in
EXCLUDE state. EXCLUDE state.
skipping to change at page 33, line 20 skipping to change at line 1450
When a router filter-mode for a group is EXCLUDE, source records are When a router filter-mode for a group is EXCLUDE, source records are
only deleted when the group timer expires. Section 6.3 describes the only deleted when the group timer expires. Section 6.3 describes the
actions that should be taken dependent upon the value of a source actions that should be taken dependent upon the value of a source
timer. timer.
6.3. IGMPv3 Source-Specific Forwarding Rules 6.3. IGMPv3 Source-Specific Forwarding Rules
When a multicast router receives a datagram from a source destined to When a multicast router receives a datagram from a source destined to
a particular group, a decision has to be made whether to forward the a particular group, a decision has to be made whether to forward the
datagram onto an attached network or not. The multicast routing datagram onto an attached network or not. The multicast routing
protocol in use is in charge of this decision, and should use the protocol in use is in charge of this decision and should use the
IGMPv3 information to ensure that all sources/groups desired on a IGMPv3 information to ensure that all sources/groups desired on a
subnetwork are forwarded to that subnetwork. IGMPv3 information does subnetwork are forwarded to that subnetwork. IGMPv3 information does
not override multicast routing information; for example, if the not override multicast routing information; for example, if the
IGMPv3 filter-mode group for G is EXCLUDE, a router may still forward IGMPv3 filter-mode group for G is EXCLUDE, a router may still forward
packets for excluded sources to a transit subnet. packets for excluded sources to a transit subnet.
To summarize, the following table describes the forwarding To summarize, Table 7 describes the forwarding suggestions made by
suggestions made by IGMP to the routing protocol for traffic IGMP to the routing protocol for traffic originating from a source
originating from a source destined to a group. It also summarizes destined to a group. It also summarizes the actions taken upon the
the actions taken upon the expiration of a source timer based on the expiration of a source timer based on the router filter-mode of the
router filter-mode of the group. group.
+=============+==========+=======================================+ +=============+==========+=======================================+
| Group | Group | Action | | Group | Group | Action |
| Filter-Mode | Timer | | | Filter-Mode | Timer | |
| | Value | | | | Value | |
+=============+==========+=======================================+ +=============+==========+=======================================+
| INCLUDE | TIMER > | Suggest to forward traffic from | | INCLUDE | TIMER > | Suggest to forward traffic from |
| | 0 | source | | | 0 | source. |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
| INCLUDE | TIMER == | Suggest to stop forwarding traffic | | INCLUDE | TIMER == | Suggest to stop forwarding traffic |
| | 0 | from source and remove source record. | | | 0 | from source and remove source record. |
| | | If there are no more source records | | | | If there are no more source records |
| | | for the group, delete group record. | | | | for the group, delete group record. |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
| INCLUDE | No | Suggest to not forward source | | INCLUDE | No | Suggest to not forward source. |
| | Source | | | | Source | |
| | Elements | | | | Elements | |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
| EXCLUDE | TIMER > | Suggest to forward traffic from | | EXCLUDE | TIMER > | Suggest to forward traffic from |
| | 0 | source | | | 0 | source. |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
| EXCLUDE | TIMER == | Suggest to not forward traffic from | | EXCLUDE | TIMER == | Suggest to not forward traffic from |
| | 0 | source (DO NOT remove record) | | | 0 | source (DO NOT remove record). |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
| EXCLUDE | No | Suggest to forward traffic from | | EXCLUDE | No | Suggest to forward traffic from |
| | Source | source | | | Source | source. |
| | Elements | | | | Elements | |
+-------------+----------+---------------------------------------+ +-------------+----------+---------------------------------------+
Table 7 Table 7
6.4. Action on Reception of Reports 6.4. Action on Reception of Reports
SSM-aware routers SHOULD ignore records that contain multicast SSM-aware routers SHOULD ignore records that contain multicast
addresses in the SSM address range if the record type is addresses in the SSM address range if the record type is
MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE. SSM-aware routers SHOULD MODE_IS_EXCLUDE or CHANGE_TO_EXCLUDE_MODE. SSM-aware routers SHOULD
ignore IGMPv1/IGMPv2 Report and IGMPv2 DONE messages that contain ignore IGMPv1/IGMPv2 Report and IGMPv2 DONE messages that contain
multicast addresses in the SSM address range, SHOULD NOT use such multicast addresses in the SSM address range, SHOULD NOT use such
Reports to establish IP forwarding state, and MAY log an error if it Reports to establish IP forwarding state, and MAY log an error if it
receives such a message. receives such a message.
6.4.1. Reception of Current-State Records 6.4.1. Reception of Current-State Records
When receiving Current-State Records, a router updates both its group When receiving Current-State Records, a router updates both its group
and source timers. In some circumstances, the reception of a type of and source timers. In some circumstances, the reception of a type of
group record will cause the router filter-mode for that group to group record will cause the router filter-mode for that group to
change. The table below describes the actions, with respect to state change. Table 8 describes the actions, with respect to state and
and timers that occur to a router's state upon reception of Current- timers that occur to a router's state upon reception of Current-
State Records. State Records.
The following notation is used to describe the updating of source The following notation is used to describe the updating of source
timers. The notation ( A, B ) will be used to represent the total timers. The notation ( A, B ) will be used to represent the total
number of sources for a particular group, where number of sources for a particular group, where
A = set of source records whose source timers > 0 (Sources that at A = set of source records whose source timers > 0 (Sources that at
least one host has requested to be forwarded) least one host has requested to be forwarded)
B = set of source records whose source timers = 0 (Sources that IGMP B = set of source records whose source timers = 0 (Sources that IGMP
will suggest to the routing protocol not to forward) will suggest to the routing protocol not to forward)
Note that there will only be two sets when a router's filter-mode for Note that there will only be two sets when a router's filter-mode for
a group is EXCLUDE. When a router's filter-mode for a group is a group is EXCLUDE. When a router's filter-mode for a group is
INCLUDE, a single set is used to describe the set of sources INCLUDE, a single set is used to describe the set of sources
requested to be forwarded (e.g., simply (A)). requested to be forwarded (e.g., simply (A)).
In the following tables, abbreviations are used for several variables In Tables 8 and 9, abbreviations are used for several variables (all
(all of which are described in detail in Section 8). The variable of which are described in detail in Section 8). The variable GMI is
GMI is an abbreviation for the Group Membership Interval, which is an abbreviation for the Group Membership Interval, which is the time
the time in which group memberships will time out. The variable LMQT in which group memberships will time out. The variable LMQT is an
is an abbreviation for the Last Member Query Time, which is the total abbreviation for the Last Member Query Time, which is the total time
time spent after Last Member Query Count retransmissions. LMQT spent after Last Member Query Count retransmissions. LMQT represents
represents the "leave latency", or the difference between the the "leave latency" or the difference between the transmission of a
transmission of a membership change and the change in the information membership change and the change in the information given to the
given to the routing protocol. routing protocol.
Within the "Actions" section of the router state tables, we use the Within the "Actions" section of the router state tables, we use the
notation 'A=J', which means that the set A of source records should notation 'A=J', which means that the set A of source records should
have their source timers set to value J. 'Delete A' means that the have their source timers set to value J. 'Delete A' means that the
set A of source records should be deleted. 'Group Timer=J' means set A of source records should be deleted. 'Group Timer=J' means
that the Group Timer for the group should be set to value J. that the Group Timer for the group should be set to value J.
Router State Report Rec'd New Router State Actions +=========+========+===========+=================+
------------ ------------ ---------------- ------- | Router | Report | New | Actions |
| State | Rec'd | Router | |
INCLUDE (A) IS_IN (B) INCLUDE (A+B) (B)=GMI | | | State | |
+=========+========+===========+=================+
INCLUDE (A) IS_EX (B) EXCLUDE (A*B,B-A) (B-A)=0 | INCLUDE | IS_IN | INCLUDE | (B)=GMI |
Delete (A-B) | (A) | (B) | (A+B) | |
Group Timer=GMI +---------+--------+-----------+-----------------+
| INCLUDE | IS_EX | EXCLUDE | (B-A)=0 |
EXCLUDE (X,Y) IS_IN (A) EXCLUDE (X+A,Y-A) (A)=GMI | (A) | (B) | (A*B,B-A) | Delete (A-B) |
| | | | Group Timer=GMI |
+---------+--------+-----------+-----------------+
| EXCLUDE | IS_IN | EXCLUDE | (A)=GMI |
| (X,Y) | (A) | (X+A,Y-A) | |
+---------+--------+-----------+-----------------+
| EXCLUDE | IS_EX | EXCLUDE | (A-X-Y)=GMI |
| (X,Y) | (A) | (A-Y,Y*A) | Delete (X-A) |
| | | | Delete (Y-A) |
| | | | Group Timer=GMI |
+---------+--------+-----------+-----------------+
EXCLUDE (X,Y) IS_EX (A) EXCLUDE (A-Y,Y*A) (A-X-Y)=GMI Table 8
Delete (X-A)
Delete (Y-A)
Group Timer=GMI
6.4.2. Reception of Filter-Mode-Change and Source-List-Change Records 6.4.2. Reception of Filter-Mode-Change and Source-List-Change Records
When a change in the global state of a group occurs in a system, the When a change in the global state of a group occurs in a system, the
system sends either a Source-List-Change Record or a Filter-Mode- system sends either a Source-List-Change Record or a Filter-Mode-
Change Record for that group. As with Current-State Records, routers Change Record for that group. As with Current-State Records, routers
must act upon these records and possibly change their own state to must act upon these records and possibly change their own state to
reflect the new desired membership state of the network. reflect the new desired membership state of the network.
Routers must query sources that are requested to be no longer Routers must query sources that are requested to be no longer
skipping to change at page 36, line 36 skipping to change at line 1596
forward the group stands without any interruption. forward the group stands without any interruption.
During a query period (i.e., Last Member Query Time seconds), the During a query period (i.e., Last Member Query Time seconds), the
IGMP component in the router continues to suggest to the routing IGMP component in the router continues to suggest to the routing
protocol that it forwards traffic from the groups or sources that it protocol that it forwards traffic from the groups or sources that it
is querying. It is not until after Last Member Query Time seconds is querying. It is not until after Last Member Query Time seconds
without receiving a record expressing interest in the queried group without receiving a record expressing interest in the queried group
or sources that the router may prune the group or sources from the or sources that the router may prune the group or sources from the
network. network.
The following table describes the changes in group state and the Table 9 describes the changes in group state and the action(s) taken
action(s) taken when receiving either Filter-Mode-Change or Source- when receiving either Filter-Mode-Change or Source-List-Change
List-Change Records. This table also describes the queries which are Records. This table also describes the queries that are sent by the
sent by the querier when a particular report is received. querier when a particular report is received.
We use the following notation for describing the queries which are We use the following notation for describing the queries that are
sent. We use the notation 'Q(G)' to describe a Group-Specific Query sent. We use the notation 'Q(G)' to describe a Group-Specific Query
to G. We use the notation 'Q(G,A)' to describe a Group-and-Source to G. We use the notation 'Q(G,A)' to describe a Group-and-Source
Specific Query to G with source-list A. If source-list A is null as Specific Query to G with source-list A. If source-list A is null as
a result of the action (e.g., A*B) then no query is sent as a result a result of the action (e.g., A*B), then no query is sent as a result
of the operation. of the operation.
In order to maintain protocol robustness, queries sent by actions in In order to maintain protocol robustness, queries sent by actions in
the table below need to be transmitted [Last Member Query Count] Table 9 need to be transmitted [Last Member Query Count] times, once
times, once every [Last Member Query Interval]. every [Last Member Query Interval].
If while scheduling new queries, there are already pending queries to If while scheduling new queries there are already pending queries to
be retransmitted for the same group, the new and pending queries have be retransmitted for the same group, the new and pending queries have
to be merged. In addition, received host reports for a group with to be merged. In addition, received host reports for a group with
pending queries may affect the contents of those queries. pending queries may affect the contents of those queries.
Section 6.6.3 describes the process of building and maintaining the Section 6.6.3 describes the process of building and maintaining the
state of pending queries. state of pending queries.
Router State Report Rec'd New Router State Actions +=========+========+=============+=====================+
------------ ------------ ---------------- ------- | Router | Report | New Router | Actions |
| State | Rec'd | State | |
INCLUDE (A) ALLOW (B) INCLUDE (A+B) (B)=GMI +=========+========+=============+=====================+
| INCLUDE | ALLOW | INCLUDE | (B)=GMI |
INCLUDE (A) BLOCK (B) INCLUDE (A) Send Q(G,A*B) | (A) | (B) | (A+B) | |
+---------+--------+-------------+---------------------+
INCLUDE (A) TO_EX (B) EXCLUDE (A*B,B-A) (B-A)=0 | INCLUDE | BLOCK | INCLUDE (A) | Send Q(G,A*B) |
Delete (A-B) | (A) | (B) | | |
Send Q(G,A*B) +---------+--------+-------------+---------------------+
Group Timer=GMI | INCLUDE | TO_EX | EXCLUDE | (B-A)=0 |
| (A) | (B) | (A*B,B-A) | Delete (A-B) |
INCLUDE (A) TO_IN (B) INCLUDE (A+B) (B)=GMI | | | | Send Q(G,A*B) |
Send Q(G,A-B) | | | | Group Timer=GMI |
+---------+--------+-------------+---------------------+
EXCLUDE (X,Y) ALLOW (A) EXCLUDE (X+A,Y-A) (A)=GMI | INCLUDE | TO_IN | INCLUDE | (B)=GMI |
| (A) | (B) | (A+B) | Send Q(G,A-B) |
EXCLUDE (X,Y) BLOCK (A) EXCLUDE (X+(A-Y),Y) (A-X-Y)=Group Timer +---------+--------+-------------+---------------------+
Send Q(G,A-Y) | EXCLUDE | ALLOW | EXCLUDE | (A)=GMI |
| (X,Y) | (A) | (X+A,Y-A) | |
EXCLUDE (X,Y) TO_EX (A) EXCLUDE (A-Y,Y*A) (A-X-Y)=Group Timer +---------+--------+-------------+---------------------+
Delete (X-A) | EXCLUDE | BLOCK | EXCLUDE | (A-X-Y)=Group Timer |
Delete (Y-A) | (X,Y) | (A) | (X+(A-Y),Y) | Send Q(G,A-Y) |
Send Q(G,A-Y) +---------+--------+-------------+---------------------+
Group Timer=GMI | EXCLUDE | TO_EX | EXCLUDE | (A-X-Y)=Group Timer |
| (X,Y) | (A) | (A-Y,Y*A) | Delete (X-A) |
| | | | Delete (Y-A) |
| | | | Send Q(G,A-Y) |
| | | | Group Timer=GMI |
+---------+--------+-------------+---------------------+
| EXCLUDE | TO_IN | EXCLUDE | (A)=GMI |
| (X,Y) | (A) | (X+A,Y-A) | Send Q(G,X-A) |
| | | | Send Q(G) |
+---------+--------+-------------+---------------------+
EXCLUDE (X,Y) TO_IN (A) EXCLUDE (X+A,Y-A) (A)=GMI Table 9
Send Q(G,X-A)
Send Q(G)
6.5. Switching Router Filter-Modes 6.5. Switching Router Filter-Modes
The group timer is used as a mechanism for transitioning the router The group timer is used as a mechanism for transitioning the router
filter-mode from EXCLUDE to INCLUDE. filter-mode from EXCLUDE to INCLUDE.
When a group timer expires with a router filter-mode of EXCLUDE, a When a group timer expires with a router filter-mode of EXCLUDE, a
router assumes that there are no systems with a filter-mode of router assumes that there are no systems with a filter-mode of
EXCLUDE present on the attached network. When a router's filter-mode EXCLUDE present on the attached network. When a router's filter-mode
for a group is EXCLUDE and the group timer expires, the router for a group is EXCLUDE and the group timer expires, the router
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For example, if a router's state for a group is EXCLUDE(X,Y) and the For example, if a router's state for a group is EXCLUDE(X,Y) and the
group timer expires for that group, the router switches to filter- group timer expires for that group, the router switches to filter-
mode of INCLUDE with state INCLUDE(X). mode of INCLUDE with state INCLUDE(X).
6.6. Action on Reception of Queries 6.6. Action on Reception of Queries
6.6.1. Timer Updates 6.6.1. Timer Updates
When a router sends or receives a query with a clear Suppress Router- When a router sends or receives a query with a clear Suppress Router-
Side Processing flag, it must update its timers to reflect the Side Processing flag, it must update its timers to reflect the
correct timeout values for the group or sources being queried. The correct timeout values for the group or sources being queried.
following table describes the timer actions when sending or receiving Table 10 describes the timer actions when sending or receiving a
a Group-Specific or Group-and-Source Specific Query with the Suppress Group-Specific or Group-and-Source Specific Query with the S flag not
Router-Side Processing flag not set. set.
+========+===================================================+ +========+===================================================+
| Query | Action | | Query | Action |
+========+===================================================+ +========+===================================================+
| Q(G,A) | Source Timer for sources in A are lowered to LMQT | | Q(G,A) | Source Timer for sources in A are lowered to LMQT |
+--------+---------------------------------------------------+ +--------+---------------------------------------------------+
| Q(G) | Group Timer is lowered to LMQT | | Q(G) | Group Timer is lowered to LMQT |
+--------+---------------------------------------------------+ +--------+---------------------------------------------------+
Table 8 Table 10
When a router sends or receives a query with the Suppress Router-Side When a router sends or receives a query with the S flag set, it will
Processing flag set, it will not update its timers. not update its timers.
6.6.2. Querier Election 6.6.2. Querier Election
IGMPv3 elects a single querier per subnet using the same querier IGMPv3 elects a single querier per subnet using the same querier
election mechanism as IGMPv2, namely by IP address. When a router election mechanism as IGMPv2, namely by IP address. When a router
receives a general query with a lower IP address, it sets the Other- receives a general query with a lower IP address, it sets the Other
Querier- Present timer to Other Querier Present Interval and ceases Querier Present timer to Other Querier Present Interval and ceases to
to send general queries on the network if it was the previously send general queries on the network if it was the previously elected
elected querier. After its Other-Querier Present timer expires, it querier. After its Other-Querier Present timer expires, it should
should begin sending General Queries. begin sending General Queries.
If a router receives an older version general query, it MUST use the If a router receives an older version general query, it MUST use the
oldest version of IGMP on the network. For a detailed description of oldest version of IGMP on the network. For a detailed description of
compatibility issues between IGMP versions see Section 7. compatibility issues between IGMP versions, see Section 7.
6.6.3. Building and Sending Specific Queries 6.6.3. Building and Sending Specific Queries
6.6.3.1. Building and Sending Group Specific Queries 6.6.3.1. Building and Sending Group-Specific Queries
When a table action "Send Q(G)" is encountered, then the group timer When a table action "Send Q(G)" is encountered, the group timer must
must be lowered to LMQT. The router must then immediately send a be lowered to LMQT. The router must then immediately send a group-
group specific query as well as schedule [Last Member Query Count - specific query as well as schedule [Last Member Query Count - 1]
1] query retransmissions to be sent every [Last Member Query query retransmissions to be sent every [Last Member Query Interval]
Interval] over [Last Member Query Time]. over [Last Member Query Time].
When transmitting a group specific query, if the group timer is When transmitting a group-specific query, if the group timer is
larger than LMQT, the "Suppress Router-Side Processing" bit is set in larger than LMQT, the "Suppress Router-Side Processing" bit is set in
the query message. the query message.
6.6.3.2. Building and Sending Group and Source Specific Queries 6.6.3.2. Building and Sending Group-and-Source-Specific Queries
When a table action "Send Q(G,X)" is encountered by a querier in the When a table action "Send Q(G,X)" is encountered by a querier in
table in Section 6.4.2, the following actions must be performed for Table 9 (Section 6.4.2), the following actions must be performed for
each of the sources in X of group G, with source timer larger than each of the sources in X of group G, with the source timer larger
LMQT: than LMQT:
* Set number of retransmissions for each source to [Last Member * Set the number of retransmissions for each source to [Last Member
Query Count]. Query Count].
* Lower source timer to LMQT. * Lower the source timer to LMQT.
The router must then immediately send a group and source specific The router must then immediately send a group and source specific
query as well as schedule [Last Member Query Count - 1] query query as well as schedule [Last Member Query Count - 1] query
retransmissions to be sent every [Last Member Query Interval] over retransmissions to be sent every [Last Member Query Interval] over
[Last Member Query Time]. The contents of these queries are [Last Member Query Time]. The contents of these queries are
calculated as follows. calculated as follows.
When building a group and source specific query for a group G, two When building a group and source specific query for group G, two
separate query messages are sent for the group. The first one has separate query messages are sent for the group. The first one has
the "Suppress Router-Side Processing" bit set and contains all the the "Suppress Router-Side Processing" bit set and contains all the
sources with retransmission state and timers greater than LMQT. The sources with retransmission state and timers greater than LMQT. The
second has the "Suppress Router-Side Processing" bit clear and second has the "Suppress Router-Side Processing" bit clear and
contains all the sources with retransmission state and timers lower contains all the sources with retransmission state and timers lower
or equal to LMQT. If either of the two calculated messages does not or equal to LMQT. If either of the two calculated messages does not
contain any sources, then its transmission is suppressed. contain any sources, then its transmission is suppressed.
Note: If a group specific query is scheduled to be transmitted at the Note: If a group-specific query is scheduled to be transmitted at the
same time as a group and source specific query for the same group, same time as a group and source specific query for the same group,
then transmission of the group and source specific message with the then transmission of the group and source specific message with the
"Suppress Router-Side Processing" bit set may be suppressed. "Suppress Router-Side Processing" bit set may be suppressed.
7. Interoperation With Older Versions of IGMP 7. Interoperation With Older Versions of IGMP
IGMP version 3 hosts and routers interoperate with hosts and routers IGMP version 3 hosts and routers interoperate with hosts and routers
that have not yet been upgraded to IGMPv3. This compatibility is that have not yet been upgraded to IGMPv3. This compatibility is
maintained by hosts and routers taking appropriate actions depending maintained by hosts and routers taking appropriate actions depending
on the versions of IGMP operating on hosts and routers within a on the versions of IGMP operating on hosts and routers within a
network. network.
7.1. Query Version Distinctions 7.1. Query Version Distinctions
The IGMP version of a Membership Query message is determined as The IGMP version of a Membership Query message is determined as
follows: follows:
IGMPv1 Query: length = 8 octets AND Max Resp Code field is zero * IGMPv1 Query: length = 8 octets AND Max Resp Code field is zero
IGMPv2 Query: length = 8 octets AND Max Resp Code field is non- * IGMPv2 Query: length = 8 octets AND Max Resp Code field is non-
zero zero
IGMPv3 Query: length >= 12 octets * IGMPv3 Query: length >= 12 octets
Query messages that do not match any of the above conditions (e.g., a Query messages that do not match any of the above conditions (e.g., a
Query of length 10 octets) MUST be silently ignored. Query of length 10 octets) MUST be silently ignored.
7.2. Group Member Behavior 7.2. Group Member Behavior
7.2.1. In the Presence of Older Version Queriers 7.2.1. In the Presence of Older Version Queriers
In order to be compatible with older version routers, IGMPv3 hosts In order to be compatible with older version routers, IGMPv3 hosts
MUST operate in version 1 and version 2 compatibility modes. IGMPv3 MUST operate in version 1 and version 2 compatibility modes. IGMPv3
hosts MUST keep state per local interface regarding the compatibility hosts MUST keep state per local interface regarding the compatibility
mode of each attached network. A host's compatibility mode is mode of each attached network. A host's compatibility mode is
determined from the Host Compatibility Mode variable which can be in determined from the Host Compatibility Mode variable, which can be in
one of three states: IGMPv1, IGMPv2 or IGMPv3. This variable is kept one of three states: IGMPv1, IGMPv2, or IGMPv3. This variable is
per interface and is dependent on the version of General Queries kept per interface and is dependent on the version of General Queries
heard on that interface as well as the Older Version Querier Present heard on that interface as well as the Older Version Querier Present
timers for the interface. timers for the interface.
In order to switch gracefully between versions of IGMP, hosts keep In order to switch gracefully between versions of IGMP, hosts keep
both an IGMPv1 Querier Present timer and an IGMPv2 Querier Present both an IGMPv1 Querier Present timer and an IGMPv2 Querier Present
timer per interface. IGMPv1 Querier Present is set to Older Version timer per interface. IGMPv1 Querier Present is set to Older Version
Querier Present Timeout seconds whenever an IGMPv1 Membership Query Querier Present Timeout seconds whenever an IGMPv1 Membership Query
is received. IGMPv2 Querier Present is set to Older Version Querier is received. IGMPv2 Querier Present is set to Older Version Querier
Present Timeout seconds whenever an IGMPv2 General Query is received. Present Timeout seconds whenever an IGMPv2 General Query is received.
The Host Compatibility Mode of an interface changes whenever an older The Host Compatibility Mode of an interface changes whenever an older
version query (than the current compatibility mode) is heard or when version query (than the current compatibility mode) is heard or when
certain timer conditions occur. When the IGMPv1 Querier Present certain timer conditions occur. When the IGMPv1 Querier Present
timer expires, a host switches to Host Compatibility mode of IGMPv2 timer expires, a host switches to Host Compatibility Mode of IGMPv2
if it has a running IGMPv2 Querier Present timer. If it does not if it has a running IGMPv2 Querier Present timer. If it does not
have a running IGMPv2 Querier Present timer then it switches to Host have a running IGMPv2 Querier Present timer, then it switches to Host
Compatibility of IGMPv3. When the IGMPv2 Querier Present timer Compatibility of IGMPv3. When the IGMPv2 Querier Present timer
expires, a host switches to Host Compatibility mode of IGMPv3. expires, a host switches to Host Compatibility Mode of IGMPv3.
The Host Compatibility Mode variable is based on whether an older The Host Compatibility Mode variable is based on whether an older
version General query was heard in the last Older Version Querier version General query was heard in the last Older Version Querier
Present Timeout seconds. The Host Compatibility mode variable value Present Timeout seconds. The Host Compatibility Mode variable value
MUST NOT be changed by an older version group-specific query. The MUST NOT be changed by an older version group-specific query. The
Host Compatibility Mode is set depending on the following: Host Compatibility Mode is set depending on the following:
+=========================+========================================+ +=========================+========================================+
| Host Compatibility Mode | Timer State | | Host Compatibility Mode | Timer State |
+=========================+========================================+ +=========================+========================================+
| IGMPv3 (default) | IGMPv2 Querier Present not running and | | IGMPv3 (default) | IGMPv2 Querier Present not running and |
| | IGMPv1 Querier Present not running | | | IGMPv1 Querier Present not running |
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
| IGMPv2 | IGMPv2 Querier Present running and | | IGMPv2 | IGMPv2 Querier Present running and |
| | IGMPv1 Querier Present not running | | | IGMPv1 Querier Present not running |
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
| IGMPv1 | IGMPv1 Querier Present running | | IGMPv1 | IGMPv1 Querier Present running |
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
Table 9 Table 11
If a host receives a query which causes its Querier Present timers to If a host receives a query that causes its Querier Present timers to
be updated and correspondingly its compatibility mode, it should be updated and correspondingly its compatibility mode, it should
switch compatibility modes immediately. switch compatibility modes immediately.
When Host Compatibility Mode is IGMPv3, a host acts using the IGMPv3 When Host Compatibility Mode is IGMPv3, a host acts using the IGMPv3
protocol on that interface. When Host Compatibility Mode is IGMPv2, protocol on that interface. When Host Compatibility Mode is IGMPv2,
a host acts in IGMPv2 compatibility mode, using only the IGMPv2 a host acts in IGMPv2 compatibility mode, using only the IGMPv2
protocol, on that interface. When Host Compatibility Mode is IGMPv1, protocol, on that interface. When Host Compatibility Mode is IGMPv1,
a host acts in IGMPv1 compatibility mode, using only the IGMPv1 a host acts in IGMPv1 compatibility mode, using only the IGMPv1
protocol on that interface. protocol on that interface.
skipping to change at page 42, line 8 skipping to change at line 1860
to the desired Max Resp Time, i.e., the full range of this field is to the desired Max Resp Time, i.e., the full range of this field is
linear and the exponential algorithm described in Section 4.1.1 is linear and the exponential algorithm described in Section 4.1.1 is
not used. not used.
Whenever a host changes its compatibility mode, it cancels all its Whenever a host changes its compatibility mode, it cancels all its
pending response and retransmission timers. pending response and retransmission timers.
An SSM-aware host that receives an IGMPv1 Query, an IGMPv2 General An SSM-aware host that receives an IGMPv1 Query, an IGMPv2 General
Query, or an IGMPv2 Group Specific Query for a multicast address in Query, or an IGMPv2 Group Specific Query for a multicast address in
the SSM address range SHOULD log an error. It is RECOMMENDED that the SSM address range SHOULD log an error. It is RECOMMENDED that
implementions provide a configuration option to disable use of Host implementations provide a configuration option to disable use of the
Compatibility Mode to allow networks to operate only in SSM mode. Host Compatibility Mode to allow networks to operate only in SSM
This configuration option SHOULD be disabled by default. mode. This configuration option SHOULD be disabled by default.
7.2.2. In the Presence of Older Version Group Members 7.2.2. In the Presence of Older Version Group Members
An IGMPv3 host may be placed on a network where there are hosts that An IGMPv3 host may be placed on a network where there are hosts that
have not yet been upgraded to IGMPv3. A host MAY allow its IGMPv3 have not yet been upgraded to IGMPv3. A host MAY allow its IGMPv3
Membership Record to be suppressed by either a Version 1 Membership Membership Record to be suppressed by either a Version 1 Membership
Report, or a Version 2 Membership Report. SSM-aware hosts MUST NOT Report, or a Version 2 Membership Report. SSM-aware hosts MUST NOT
allow its IGMPv3 Membership Record to be suppressed. allow its IGMPv3 Membership Record to be suppressed.
7.3. Multicast Router Behavior 7.3. Multicast Router Behavior
skipping to change at page 42, line 34 skipping to change at line 1886
IGMPv3 routers may be placed on a network where at least one router IGMPv3 routers may be placed on a network where at least one router
on the network has not yet been upgraded to IGMPv3. The following on the network has not yet been upgraded to IGMPv3. The following
requirements apply: requirements apply:
* If any older versions of IGMP are present on routers, the querier * If any older versions of IGMP are present on routers, the querier
MUST use the lowest version of IGMP present on the network. This MUST use the lowest version of IGMP present on the network. This
must be administratively assured; routers that desire to be must be administratively assured; routers that desire to be
compatible with IGMPv1 and IGMPv2 MUST have a configuration option compatible with IGMPv1 and IGMPv2 MUST have a configuration option
to act in IGMPv1 or IGMPv2 compatibility modes. When in IGMPv1 to act in IGMPv1 or IGMPv2 compatibility modes. When in IGMPv1
mode, routers MUST send Periodic Queries with a Max Resp Code of 0 mode, routers MUST send Periodic Queries with a Max Resp Code of 0
and truncated at the Group Address field (i.e., 8 bytes long), and and truncated at the Group Address field (i.e., 8 bytes long) and
MUST ignore Leave Group messages. They SHOULD also warn about MUST ignore Leave Group messages. They SHOULD also warn about
receiving an IGMPv2 or IGMPv3 query, although such warnings MUST receiving an IGMPv2 or IGMPv3 query, although such warnings MUST
be rate-limited. When in IGMPv2 mode, routers MUST send Periodic be rate-limited. When in IGMPv2 mode, routers MUST send Periodic
Queries truncated at the Group Address field (i.e., 8 bytes long), Queries truncated at the Group Address field (i.e., 8 bytes long)
and SHOULD also warn about receiving an IGMPv3 query (such and SHOULD also warn about receiving an IGMPv3 query (such
warnings MUST be rate-limited). They also MUST fill in the Max warnings MUST be rate-limited). They also MUST fill in the Max
Resp Time in the Max Resp Code field, i.e., the exponential Resp Time in the Max Resp Code field, i.e., the exponential
algorithm described in Section 4.1.1 is not used. algorithm described in Section 4.1.1 is not used.
* If a router is not explicitly configured to use IGMPv1 or IGMPv2 * If a router is not explicitly configured to use IGMPv1 or IGMPv2
and hears an IGMPv1 Query or IGMPv2 General Query, it SHOULD log a and hears an IGMPv1 Query or IGMPv2 General Query, it SHOULD log a
warning. These warnings MUST be rate-limited. warning. These warnings MUST be rate-limited.
* It is RECOMMENDED that implementions provide a configuration * It is RECOMMENDED that implementations provide a configuration
option to disable use of compatibility mode to allow networks to option to disable use of compatibility mode to allow networks to
operate only in SSM mode. This configuration option SHOULD be operate only in SSM mode. This configuration option SHOULD be
disabled by default. disabled by default.
7.3.2. In the Presence of Older Version Group Members 7.3.2. In the Presence of Older Version Group Members
IGMPv3 routers may be placed on a network where there are hosts that IGMPv3 routers may be placed on a network where there are hosts that
have not yet been upgraded to IGMPv3. In order to be compatible with have not yet been upgraded to IGMPv3. In order to be compatible with
older version hosts, IGMPv3 routers MUST operate in version 1 and older version hosts, IGMPv3 routers MUST operate in version 1 and
version 2 compatibility modes. IGMPv3 routers keep a compatibility version 2 compatibility modes. IGMPv3 routers keep a compatibility
mode per group record. A group's compatibility mode is determined mode per group record. A group's compatibility mode is determined
from the Group Compatibility Mode variable which can be in one of from the Group Compatibility Mode variable, which can be in one of
three states: IGMPv1, IGMPv2 or IGMPv3. This variable is kept per three states: IGMPv1, IGMPv2, or IGMPv3. This variable is kept per
group record and is dependent on the version of Membership Reports group record and is dependent on the version of Membership Reports
heard for that group as well as the Older Version Host Present timer heard for that group as well as the Older Version Host Present timer
for the group. for the group.
In order to switch gracefully between versions of IGMP, routers keep In order to switch gracefully between versions of IGMP, routers keep
an IGMPv1 Host Present timer and an IGMPv2 Host Present timer per an IGMPv1 Host Present timer and an IGMPv2 Host Present timer per
group record. The IGMPv1 Host Present timer is set to Older Version group record. The IGMPv1 Host Present timer is set to Older Version
Host Present Timeout seconds whenever an IGMPv1 Membership Report is Host Present Timeout seconds whenever an IGMPv1 Membership Report is
received. The IGMPv2 Host Present timer is set to Older Version Host received. The IGMPv2 Host Present timer is set to Older Version Host
Present Timeout seconds whenever an IGMPv2 Membership Report is Present Timeout seconds whenever an IGMPv2 Membership Report is
received. received.
The Group Compatibility Mode of a group record changes whenever an The Group Compatibility Mode of a group record changes whenever an
older version report (than the current compatibility mode) is heard older version report (than the current compatibility mode) is heard
or when certain timer conditions occur. When the IGMPv1 Host Present or when certain timer conditions occur. When the IGMPv1 Host Present
timer expires, a router switches to Group Compatibility mode of timer expires, a router switches to Group Compatibility Mode of
IGMPv2 if it has a running IGMPv2 Host Present timer. If it does not IGMPv2 if it has a running IGMPv2 Host Present timer. If it does not
have a running IGMPv2 Host Present timer then it switches to Group have a running IGMPv2 Host Present timer, then it switches to Group
Compatibility of IGMPv3. When the IGMPv2 Host Present timer expires Compatibility Mode of IGMPv3. When the IGMPv2 Host Present timer
and the IGMPv1 Host Present timer is not running, a router switches expires and the IGMPv1 Host Present timer is not running, a router
to Group Compatibility mode of IGMPv3. Note that when a group switches to Group Compatibility Mode of IGMPv3. Note that when a
switches back to IGMPv3 mode, it takes some time to regain source- group switches back to IGMPv3 mode, it takes some time to regain
specific state information. Source-specific information will be source- specific state information. Source-specific information will
learned during the next General Query, but sources that should be be learned during the next General Query, but sources that should be
blocked will not be blocked until [Group Membership Interval] after blocked will not be blocked until [Group Membership Interval] after
that. that.
The Group Compatibility Mode variable is based on whether an older The Group Compatibility Mode variable is based on whether an older
version report was heard in the last Older Version Host Present version report was heard in the last Older Version Host Present
Timeout seconds. The Group Compatibility Mode is set depending on Timeout seconds. The Group Compatibility Mode is set depending on
the following: the following:
+==========================+=====================================+ +==========================+=====================================+
| Group Compatibility Mode | Timer State | | Group Compatibility Mode | Timer State |
+==========================+=====================================+ +==========================+=====================================+
| IGMPv3 (default) | IGMPv2 Host Present not running and | | IGMPv3 (default) | IGMPv2 Host Present not running and |
| | IGMPv1 Host Present not running | | | IGMPv1 Host Present not running |
+--------------------------+-------------------------------------+ +--------------------------+-------------------------------------+
| IGMPv2 | IGMPv2 Host Present running and | | IGMPv2 | IGMPv2 Host Present running and |
| | IGMPv1 Host Present not running | | | IGMPv1 Host Present not running |
+--------------------------+-------------------------------------+ +--------------------------+-------------------------------------+
| IGMPv1 | IGMPv1 Host Present running | | IGMPv1 | IGMPv1 Host Present running |
+--------------------------+-------------------------------------+ +--------------------------+-------------------------------------+
Table 10 Table 12
If a router receives a report which causes its older Host Present If a router receives a report that causes its older Host Present
timers to be updated and correspondingly its compatibility mode, it timers to be updated and correspondingly its compatibility mode, it
SHOULD switch compatibility modes immediately. SHOULD switch compatibility modes immediately.
When Group Compatibility Mode is IGMPv3, a router acts using the When Group Compatibility Mode is IGMPv3, a router acts using the
IGMPv3 protocol for that group. IGMPv3 protocol for that group.
When Group Compatibility Mode is IGMPv2, a router internally When Group Compatibility Mode is IGMPv2, a router internally
translates the following IGMPv2 messages for that group to their translates the following IGMPv2 messages for that group to their
IGMPv3 equivalents: IGMPv3 equivalents:
+================+===================+ +================+===================+
| IGMPv2 Message | IGMPv3 Equivalent | | IGMPv2 Message | IGMPv3 Equivalent |
+================+===================+ +================+===================+
| Report | IS_EX( {} ) | | Report | IS_EX( {} ) |
+----------------+-------------------+ +----------------+-------------------+
| Leave | TO_IN( {} ) | | Leave | TO_IN( {} ) |
+----------------+-------------------+ +----------------+-------------------+
Table 11 Table 13
IGMPv3 BLOCK messages are ignored, as are source-lists in TO_EX() IGMPv3 BLOCK messages are ignored, as are source-lists in TO_EX()
messages (i.e., any TO_EX() message is treated as TO_EX( {} )). messages (i.e., any TO_EX() message is treated as TO_EX( {} )).
When Group Compatibility Mode is IGMPv1, a router internally When Group Compatibility Mode is IGMPv1, a router internally
translates the following IGMPv1 and IGMPv2 messages for that group to translates the following IGMPv1 and IGMPv2 messages for that group to
their IGMPv3 equivalents: their IGMPv3 equivalents:
+================+===================+ +================+===================+
| IGMPv2 Message | IGMPv3 Equivalent | | IGMPv2 Message | IGMPv3 Equivalent |
+================+===================+ +================+===================+
| v1 Report | IS_EX( {} ) | | v1 Report | IS_EX( {} ) |
+----------------+-------------------+ +----------------+-------------------+
| v2 Report | IS_EX( {} ) | | v2 Report | IS_EX( {} ) |
+----------------+-------------------+ +----------------+-------------------+
Table 12 Table 14
In addition to ignoring IGMPv3 BLOCK messages and source-lists in In addition to ignoring IGMPv3 BLOCK messages and source-lists in
TO_EX() messages as in IGMPv2 Group Compatibility Mode, IGMPv2 Leave TO_EX() messages as in IGMPv2 Group Compatibility Mode, IGMPv2 Leave
messages and IGMPv3 TO_IN() messages are also ignored. messages and IGMPv3 TO_IN() messages are also ignored.
8. List of Timers, Counters and Their Default Values 8. List of Timers, Counters, and Their Default Values
Most of these timers are configurable. If non-default settings are Most of these timers are configurable. If non-default settings are
used, they MUST be consistent among all systems on a single link. used, they MUST be consistent among all systems on a single link.
Note that parentheses are used to group expressions to make the Note that parentheses are used to group expressions to make the
algebra clear. algebra clear.
8.1. Robustness Variable 8.1. Robustness Variable
The Robustness Variable allows tuning for the expected packet loss on The Robustness Variable allows tuning for the expected packet loss on
a network. If a network is expected to be lossy, the Robustness a network. If a network is expected to be lossy, the Robustness
Variable may be increased. IGMP is robust to (Robustness Variable - Variable may be increased. IGMP is robust to (Robustness Variable -
1) packet losses. The Robustness Variable MUST NOT be zero, and 1) packet losses. The Robustness Variable MUST NOT be zero and
SHOULD NOT be one. Default: 2 SHOULD NOT be one. Default: 2.
8.2. Query Interval 8.2. Query Interval
The Query Interval is the interval between General Queries sent by The Query Interval is the interval between General Queries sent by
the Querier. Default: 125 seconds. the Querier. Default: 125 seconds.
By varying the [Query Interval], an administrator may tune the number By varying the [Query Interval], an administrator may tune the number
of IGMP messages on the network; larger values cause IGMP Queries to of IGMP messages on the network; larger values cause IGMP Queries to
be sent less often. be sent less often.
8.3. Query Response Interval 8.3. Query Response Interval
The Max Response Time used to calculate the Max Resp Code inserted The Query Response Interval uses the Max Response Time to calculate
into the periodic General Queries. Default: 100 (10 seconds) the Max Resp Code that is inserted into the periodic General Queries.
Default: 100 (10 seconds).
By varying the [Query Response Interval], an administrator may tune By varying the [Query Response Interval], an administrator may tune
the burstiness of IGMP messages on the network; larger values make the burstiness of IGMP messages on the network; larger values make
the traffic less bursty, as host responses are spread out over a the traffic less bursty, as host responses are spread out over a
larger interval. The number of seconds represented by the [Query larger interval. The number of seconds represented by the [Query
Response Interval] must be less than the [Query Interval]. Response Interval] must be less than the [Query Interval].
8.4. Group Membership Interval 8.4. Group Membership Interval
The Group Membership Interval is the amount of time that must pass The Group Membership Interval is the amount of time that must pass
before a multicast router decides there are no more members of a before a multicast router decides there are no more members of a
group or a particular source on a network. group or a particular source on a network.
This value MUST be ((the Robustness Variable) times (the Query This value MUST be ((the Robustness Variable) times (the Query
Interval)) plus (2 * Query Response Interval). Interval)) plus (2 * Query Response Interval).
8.5. Other Querier Present Interval 8.5. Other Querier Present Interval
The Other Querier Present Interval is the length of time that must The Other Querier Present Interval is the length of time that must
pass before a multicast router decides that there is no longer pass before a multicast router decides that there is no longer
another multicast router which should be the querier. This value another multicast router that should be the querier. This value MUST
MUST be ((the Robustness Variable) times (the Query Interval)) plus be ((the Robustness Variable) times (the Query Interval)) plus (one
(one half of one Query Response Interval). half of one Query Response Interval).
8.6. Startup Query Interval 8.6. Startup Query Interval
The Startup Query Interval is the interval between General Queries The Startup Query Interval is the interval between General Queries
sent by a Querier on startup. Default: 1/4 the Query Interval. sent by a Querier on startup. Default: 1/4 the Query Interval.
8.7. Startup Query Count 8.7. Startup Query Count
The Startup Query Count is the number of Queries sent out on startup, The Startup Query Count is the number of Queries sent out on startup,
separated by the Startup Query Interval. Default: the Robustness separated by the Startup Query Interval. Default: The Robustness
Variable. Variable.
8.8. Last Member Query Interval 8.8. Last Member Query Interval
The Last Member Query Interval is the Max Response Time used to The Last Member Query Interval (LMQI) is the Max Response Time used
calculate the Max Resp Code inserted into Group-Specific Queries sent to calculate the Max Resp Code that is inserted into Group-Specific
in response to Leave Group messages. It is also the Max Response Queries sent in response to Leave Group messages. It is also the Max
Time used in calculating the Max Resp Code for Group-and-Source- Response Time used in calculating the Max Resp Code for Group-and-
Specific Query messages. Default: 10 (1 second) Source-Specific Query messages. Default: 10 (1 second).
Note that for values of LMQI greater than 12.8 seconds, a limited set Note that for values of LMQI greater than 12.8 seconds, a limited set
of values can be represented, corresponding to sequential values of of values can be represented, corresponding to sequential values of
Max Resp Code. When converting a configured time to a Max Resp Code Max Resp Code. When converting a configured time to a Max Resp Code
value, it is recommended to use the exact value if possible, or the value, it is recommended to use the exact value, if possible, or the
next lower value if the requested value is not exactly representable. next lower value if the requested value is not exactly representable.
This value may be tuned to modify the "leave latency" of the network. This value may be tuned to modify the "leave latency" of the network.
A reduced value results in reduced time to detect the loss of the A reduced value results in reduced time to detect the loss of the
last member of a group or source. last member of a group or source.
8.9. Last Member Query Count 8.9. Last Member Query Count
The Last Member Query Count is the number of Group-Specific Queries The Last Member Query Count is the number of Group-Specific Queries
sent before the router assumes there are no local members. The Last sent before the router assumes there are no local members. The Last
Member Query Count is also the number of Group-and-Source-Specific Member Query Count is also the number of Group-and-Source-Specific
Queries sent before the router assumes there are no listeners for a Queries sent before the router assumes there are no listeners for a
particular source. Default: the Robustness Variable. particular source. Default: The Robustness Variable.
8.10. Last Member Query Time 8.10. Last Member Query Time
The Last Member Query Time is the time value represented by the Last The Last Member Query Time is the time value represented by the Last
Member Query Interval, multiplied by the Last Member Query Count. It Member Query Interval, multiplied by the Last Member Query Count. It
is not a tunable value, but may be tuned by changing its components. is not a tunable value, but it may be tuned by changing its
components.
8.11. Unsolicited Report Interval 8.11. Unsolicited Report Interval
The Unsolicited Report Interval is the time between repetitions of a The Unsolicited Report Interval is the time between repetitions of a
host's initial report of membership in a group. Default: 1 second. host's initial report of membership in a group. Default: 1 second.
8.12. Older Version Querier Present Interval 8.12. Older Version Querier Present Interval
The Older Version Querier Present Interval is the timeout for The Older Version Querier Present Interval is the timeout for
transitioning a host back to IGMPv3 mode once an older version query transitioning a host back to IGMPv3 mode once an older version query
skipping to change at page 47, line 40 skipping to change at line 2120
Interval. Interval.
It is RECOMMENDED to use the default values for calculating the It is RECOMMENDED to use the default values for calculating the
interval value as hosts do not know the values configured on the interval value as hosts do not know the values configured on the
querying routers. This value SHOULD be [Robustness Variable] times querying routers. This value SHOULD be [Robustness Variable] times
[Query Interval] plus (10 times the Max Resp Time in the last [Query Interval] plus (10 times the Max Resp Time in the last
received query message). received query message).
8.13. Older Host Present Interval 8.13. Older Host Present Interval
The Older Host Present Interval is the time-out for transitioning a The Older Host Present Interval is the timeout for transitioning a
group back to IGMPv3 mode once an older version report is sent for group back to IGMPv3 mode once an older version report is sent for
that group. When an older version report is received, routers set that group. When an older version report is received, routers set
their Older Host Present Timer to Older Host Present Interval. their Older Host Present Timer to Older Host Present Interval.
This value MUST be ((the Robustness Variable) times (the Query This value MUST be ((the Robustness Variable) times (the Query
Interval)) plus (one Query Response Interval). Interval)) plus (one Query Response Interval).
8.14. Configuring Timers 8.14. Configuring Timers
This section is meant to provide advice to network administrators on This section is meant to provide advice to network administrators on
skipping to change at page 49, line 6 skipping to change at line 2171
in Group-Specific and Source-and-Group-Specific Queries extends the in Group-Specific and Source-and-Group-Specific Queries extends the
leave latency. (The leave latency is the time between when the last leave latency. (The leave latency is the time between when the last
member stops listening to a source or group and when the traffic member stops listening to a source or group and when the traffic
stops flowing.) The expected rate of Report messages can be stops flowing.) The expected rate of Report messages can be
calculated by dividing the expected number of Reporters by the Max calculated by dividing the expected number of Reporters by the Max
Response Time. The Max Response Time may be dynamically calculated Response Time. The Max Response Time may be dynamically calculated
per Query by using the expected number of Reporters for that Query as per Query by using the expected number of Reporters for that Query as
follows: follows:
+===========================+===============================+ +===========================+===============================+
| Query Type | Expected number of Reporters | | Query Type | Expected Number of Reporters |
+===========================+===============================+ +===========================+===============================+
| General Query | All systems on subnetwork | | General Query | All systems on the subnetwork |
+---------------------------+-------------------------------+ +---------------------------+-------------------------------+
| Group-Specific Query | All systems that had | | Group-Specific Query | All systems that had |
| | expressed interest in the | | | expressed interest in the |
| | group on the subnetwork | | | group on the subnetwork |
+---------------------------+-------------------------------+ +---------------------------+-------------------------------+
| Source-and-Group-Specific | All systems on the subnetwork | | Source-and-Group-Specific | All systems on the subnetwork |
| Query | that had expressed interest | | Query | that had expressed interest |
| | in the source and group | | | in the source and group |
+---------------------------+-------------------------------+ +---------------------------+-------------------------------+
Table 13 Table 15
A router is not required to calculate these populations or tune the A router is not required to calculate these populations or tune the
Max Response Time dynamically; these are simply guidelines. Max Response Time dynamically; these are simply guidelines.
9. Security Considerations 9. Security Considerations
IGMP does provide any form of confidentiality. This means any device IGMP provides any form of confidentiality. This means any device on
on a link can passively receive any IGMP message on the link. Such a link can passively receive any IGMP message on the link. Such
access can lead to privacy concerns around potentially sensitive access can lead to privacy concerns around potentially sensitive
multicast groups or the ability to identify/map the devices on a multicast groups or the ability to identify/map the devices on a
link. link.
We consider the ramifications of a forged message of each type, and We consider the ramifications of a forged message of each type and
describe the usage of IPsec AH to authenticate messages if desired. describe the usage of an IPsec Authentication Header (AH) to
authenticate messages if desired.
9.1. Query Message 9.1. Query Message
A forged Query message from a machine with a lower IP address than A forged Query message from a machine with a lower IP address than
the current Querier will cause Querier duties to be assigned to the the current Querier will cause Querier duties to be assigned to the
forger. If the forger then sends no more Query messages, other forger. If the forger then sends no more Query messages, other
routers' Other Querier Present timer will time out and one will routers' Other Querier Present timer will time out and one will
resume the role of Querier. During this time, if the forger ignores resume the role of Querier. During this time, if the forger ignores
Leave Messages, traffic might flow to groups with no members for up Leave messages, traffic might flow to groups with no members for up
to [Group Membership Interval]. to [Group Membership Interval].
A DoS attack on a host could be staged through forged Group-and- A Denial-of-Service (DoS) attack on a host could be staged through
Source-Specific Queries. The attacker can find out about membership forged Group-and- Source-Specific Queries. The attacker can find out
of a specific host with a general query. After that it could send a about membership of a specific host with a general query. After
large number of Group-and-Source-Specific queries, each with a large that, it could send a large number of Group-and-Source-Specific
source list and the Maximum Response Time set to a large value. The queries, each with a large source list and the Maximum Response Time
host will have to store and maintain the sources specified in all of set to a large value. The host will have to store and maintain the
those queries for as long as it takes to send the delayed response. sources specified in all of those queries for as long as it takes to
This would consume both memory and CPU cycles in order to augment the send the delayed response. This would consume both memory and CPU
recorded sources with the source lists included in the successive cycles in order to augment the recorded sources with the source lists
queries. included in the successive queries.
To protect against such a DoS attack, a host stack implementation To protect against such a DoS attack, a host stack implementation
could restrict the number of Group-and-Source-Specific Queries per could restrict the number of Group-and-Source-Specific Queries per
group membership within this interval, and/or record only a limited group membership within this interval and/or record only a limited
number of sources. number of sources.
Forged Query messages from the local network can be easily traced. Forged Query messages from the local network can be easily traced.
There are three measures necessary to defend against externally There are three measures necessary to defend against externally
forged Queries: forged Queries:
* Routers SHOULD NOT forward Queries. This is easier for a router * Routers SHOULD NOT forward Queries. This is easier for a router
to accomplish if the Query carries the Router-Alert option. to accomplish if the Query carries the Router Alert option.
* Hosts SHOULD ignore v2 or v3 Queries without the Router-Alert * Hosts SHOULD ignore v2 or v3 Queries without the Router Alert
option. option.
* Hosts SHOULD ignore v1, v2 or v3 General Queries sent to a * Hosts SHOULD ignore v1, v2, or v3 General Queries sent to a
multicast address other than 224.0.0.1, the all-systems address. multicast address other than 224.0.0.1, the all-systems address.
9.2. Current-State Report messages 9.2. Current-State Report Messages
A forged Report message may cause multicast routers to think there A forged Report message may cause multicast routers to think there
are members of a group on a network when there are not. Forged are members of a group on a network when there are not. Forged
Report messages from the local network are meaningless, since joining Report messages from the local network are meaningless, as joining a
a group on a host is generally an unprivileged operation, so a local group on a host is generally an unprivileged operation, so a local
user may trivially gain the same result without forging any messages. user may trivially gain the same result without forging any messages.
Forged Report messages from external sources are more troublesome; Forged Report messages from external sources are more troublesome;
there are two defenses against externally forged Reports: there are two defenses against externally forged Reports:
* Ignore the Report if you cannot identify the source address of the 1. Ignore the Report if you cannot identify the source address of
packet as belonging to a network assigned to the interface on the packet as belonging to a network assigned to the interface on
which the packet was received. This solution means that Reports which the packet was received. This solution means that Reports
sent by mobile hosts without addresses on the local network will sent by mobile hosts without addresses on the local network will
be ignored. Report messages with a source address of 0.0.0.0 be ignored. Report messages with a source address of 0.0.0.0
SHOULD be accepted on any interface. SHOULD be accepted on any interface.
* Ignore Report messages without Router Alert options [RFC2113], and 2. Ignore Report messages without Router Alert options [RFC2113] and
require that routers not forward Report messages. (The require routers to not forward Report messages. (The requirement
requirement is not a requirement of generalized filtering in the is not a requirement of generalized filtering in the forwarding
forwarding path, since the packets already have Router Alert path, as the packets already have Router Alert options in them.)
options in them.) This solution breaks backwards compatibility This solution breaks backwards compatibility with implementations
with implementations of IGMPv1 or earlier versions of IGMPv2 which of IGMPv1 or earlier versions of IGMPv2 that did not require a
did not require Router Alert. Router Alert.
A forged Version 1 Report Message may put a router into "version 1 A forged Version 1 Report Message may put a router into "version 1
members present" state for a particular group, meaning that the members present" state for a particular group, meaning that the
router will ignore Leave messages. This can cause traffic to flow to router will ignore Leave messages. This can cause traffic to flow to
groups with no members for up to [Group Membership Interval]. This groups with no members for up to [Group Membership Interval]. This
can be solved by providing routers with a configuration switch to can be solved by providing routers with a configuration switch to
ignore Version 1 messages completely. This breaks automatic ignore Version 1 messages completely. This breaks automatic
compatibility with Version 1 hosts, so should only be used in compatibility with Version 1 hosts, so it should only be used in
situations where "fast leave" is critical. situations where "fast leave" is critical.
A forged Version 2 Report Message may put a router into "version 2 A forged Version 2 Report Message may put a router into "version 2
members present" state for a particular group, meaning that the members present" state for a particular group, meaning that the
router will ignore IGMPv3 source-specific state messages. This can router will ignore IGMPv3 source-specific state messages. This can
cause traffic to flow from unwanted sources for up to [Group cause traffic to flow from unwanted sources for up to [Group
Membership Interval]. This can be solved by providing routers with a Membership Interval]. This can be solved by providing routers with a
configuration switch to ignore Version 2 messages completely. This configuration switch to ignore Version 2 messages completely. This
breaks automatic compatibility with Version 2 hosts, so should only breaks automatic compatibility with Version 2 hosts, so it should
be used in situations where source include and exclude is critical. only be used in situations where source include and exclude is
critical.
9.3. State-Change Report Messages 9.3. State-Change Report Messages
A forged State-Change Report message will cause the Querier to send A forged State-Change Report message will cause the Querier to send
out Group-Specific or Source-and-Group-Specific Queries for the group out Group-Specific or Source-and-Group-Specific Queries for the group
in question. This causes extra processing on each router and on each in question. This causes extra processing on each router and on each
member of the group, but can not cause loss of desired traffic. member of the group, but it cannot cause loss of desired traffic.
There are two defenses against externally forged State-Change Report There are two defenses against externally forged State-Change Report
messages: messages:
* Ignore the State-Change Report message if you cannot identify the 1. Ignore the State-Change Report message if you cannot identify the
source address of the packet as belonging to a subnet assigned to source address of the packet as belonging to a subnet assigned to
the interface on which the packet was received. This solution the interface on which the packet was received. This solution
means that State-Change Report messages sent by mobile hosts means that State-Change Report messages sent by mobile hosts
without addresses on the local subnet will be ignored. State- without addresses on the local subnet will be ignored. State-
Change Report messages with a source address of 0.0.0.0 SHOULD be Change Report messages with a source address of 0.0.0.0 SHOULD be
accepted on any interface. accepted on any interface.
* Ignore State-Change Report messages without Router Alert options 2. Ignore State-Change Report messages without Router Alert options
[RFC2113], and require that routers not forward State-Change [RFC2113] and require routers to not forward State-Change Report
Report messages. (The requirement is not a requirement of messages. (The requirement is not a requirement of generalized
generalized filtering in the forwarding path, since the packets filtering in the forwarding path, as the packets already have
already have Router Alert options in them.) Router Alert options in them.)
9.4. IPsec Usage 9.4. IPsec Usage
In addition to these measures, IPsec in Authentication Header mode In addition to these measures, IPsec in AH mode [RFC4302] may be used
[RFC4302] may be used to protect against remote attacks by ensuring to protect against remote attacks by ensuring that IGMPv3 messages
that IGMPv3 messages came from a system on the LAN (or, more came from a system on the LAN (or, more specifically, from a system
specifically, a system with the proper key). When using IPsec, the with the proper key). When using IPsec, the messages sent to
messages sent to 224.0.0.1 and 224.0.0.22 should be authenticated 224.0.0.1 and 224.0.0.22 should be authenticated using AH. When
using AH. When keying, there are two possibilities: keying, there are two possibilities:
1. Use a symmetric signature algorithm with a single key for the LAN 1. Use a symmetric signature algorithm with a single key for the LAN
(or a key for each group). This allows validation that a packet (or a key for each group). This allows validation that a packet
was sent by a system with the key. This has the limitation that was sent by a system with the key. This has the limitation that
any system with the key can forge a message; it is not possible any system with the key can forge a message; it is not possible
to authenticate the individual sender precisely. It also to authenticate the individual sender precisely. It also
requires disabling IPSec's Replay Protection. requires disabling IPsec's Replay Protection.
2. When appropriate key management standards have been developed, 2. When appropriate key management standards have been developed,
use an asymmetric signature algorithm. All systems need to know use an asymmetric signature algorithm. All systems need to know
the public key of all routers, and all routers need to know the the public key of all routers, and all routers need to know the
public key of all systems. This requires a large amount of key public key of all systems. This requires a large amount of key
management but has the advantage that senders can be management but has the advantage that senders can be
authenticated individually so e.g., a host cannot forge a message authenticated individually so, e.g., a host cannot forge a
that only routers should be allowed to send. message that only routers should be allowed to send.
This solution only directly applies to Query and Leave messages in This solution only directly applies to Query and Leave messages in
IGMPv1 and IGMPv2, since Reports are sent to the group being reported IGMPv1 and IGMPv2 as Reports are sent to the group being reported,
and it is not feasible to agree on a key for host-to-router and it is not feasible to agree on a key for host-to-router
communication for arbitrary multicast groups. communication for arbitrary multicast groups.
10. IANA Considerations 10. IANA Considerations
All IGMP types described in this document are managed via All IGMP types described in this document are managed via [RFC9778].
[I-D.ietf-pim-3228bis].
References to RFC 3376 that currently exist in IANA registries are to
be updated to reference this document. This includes a reference in
the IGMP Type Numbers registry and the informational reference in the
IPFIX Information Elements registry.
11. Contributors
Brad Cain, Steve Deering, Isidor Kouvelas, Bill Fenner, and Ajit
Thyagarajan are the authors of RFC 3376, which forms the bulk of the
content contained herein.
Anuj Budhiraja, Toerless Eckert, Olufemi Komolafe and Tim Winters
have contributed valuable content to this version of the
specification.
12. Acknowledgments
We would like to thank Ran Atkinson, Luis Costa, Toerless Eckert,
Dino Farinacci, Serge Fdida, Wilbert de Graaf, Sumit Gupta, Mark
Handley, Bob Quinn, Michael Speer, Dave Thaler and Rolland Vida for
comments and suggestions on RFC 3376.
Stig Venaas, Hitoshi Asaeda, and Mike McBride have provided valuable
feedback on this version of the specification and we thank them for
their input.
13. References IANA has replaced each reference to [RFC3376] with a reference to
this document in both the "IGMP Type Numbers" and "IPFIX Information
Elements" registries.
13.1. Normative References 11. References
[I-D.ietf-pim-3228bis] 11.1. Normative References
Haberman, B., "IANA Considerations for Internet Group
Management Protocols", Work in Progress, Internet-Draft,
draft-ietf-pim-3228bis-06, 13 June 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pim-
3228bis-06>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5, [RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989, RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>. <https://www.rfc-editor.org/info/rfc1112>.
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113, [RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
DOI 10.17487/RFC2113, February 1997, DOI 10.17487/RFC2113, February 1997,
<https://www.rfc-editor.org/info/rfc2113>. <https://www.rfc-editor.org/info/rfc2113>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 54, line 13 skipping to change at line 2383
August 2006, <https://www.rfc-editor.org/info/rfc4604>. August 2006, <https://www.rfc-editor.org/info/rfc4604>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>. <https://www.rfc-editor.org/info/rfc4607>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
13.2. Informative References [RFC9778] Haberman, B., Ed., "IANA Considerations for Internet Group
Management Protocols", BCP 57, RFC 9778,
DOI 10.17487/RFC9778, March 2025,
<https://www.rfc-editor.org/info/rfc9778>.
11.2. Informative References
[RFC1071] Braden, R., Borman, D., and C. Partridge, "Computing the [RFC1071] Braden, R., Borman, D., and C. Partridge, "Computing the
Internet checksum", RFC 1071, DOI 10.17487/RFC1071, Internet checksum", RFC 1071, DOI 10.17487/RFC1071,
September 1988, <https://www.rfc-editor.org/info/rfc1071>. September 1988, <https://www.rfc-editor.org/info/rfc1071>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>. <https://www.rfc-editor.org/info/rfc3376>.
skipping to change at page 54, line 38 skipping to change at line 2413
[RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface [RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
Extensions for Multicast Source Filters", RFC 3678, Extensions for Multicast Source Filters", RFC 3678,
DOI 10.17487/RFC3678, January 2004, DOI 10.17487/RFC3678, January 2004,
<https://www.rfc-editor.org/info/rfc3678>. <https://www.rfc-editor.org/info/rfc3678>.
Appendix A. Design Rationale Appendix A. Design Rationale
A.1. The Need for State-Change Messages A.1. The Need for State-Change Messages
IGMPv3 specifies two types of Membership Reports: Current-State and IGMPv3 specifies two types of Membership Reports: Current-State and
State Change. This section describes the rationale for the need for State Change. This section describes the rationale for needing both
both these types of Reports. types of Reports.
Routers need to distinguish Membership Reports that were sent in Routers need to distinguish Membership Reports that were sent in
response to Queries from those that were sent as a result of a change response to Queries from those that were sent as a result of a change
in interface state. Membership reports that are sent in response to in interface state. Membership reports that are sent in response to
Membership Queries are used mainly to refresh the existing state at Membership Queries are used mainly to refresh the existing state at
the router; they typically do not cause transitions in state at the the router; they typically do not cause transitions in state at the
router. Membership Reports that are sent in response to changes in router. Membership Reports that are sent in response to changes in
interface state require the router to take some action in response to interface state require the router to take some action in response to
the received report (see Section 6.4). the received report (see Section 6.4).
The inability to distinguish between the two types of reports would The inability to distinguish between the two types of reports would
force a router to treat all Membership Reports as potential changes force a router to treat all Membership Reports as potential changes
in state and could result in increased processing at the router as in state, and it could result in increased processing at the router
well as an increase in IGMP traffic on the network. as well as an increase in IGMP traffic on the network.
A.2. Host Suppression A.2. Host Suppression
In IGMPv1 and IGMPv2, a host would cancel sending a pending In IGMPv1 and IGMPv2, a host would cancel sending pending membership
membership reports if a similar report was observed from another reports if a similar report was observed from another member on the
member on the network. In IGMPv3, this suppression of host network. In IGMPv3, this suppression of host membership reports has
membership reports has been removed. The following points explain been removed. The following points explain the reasons behind this
the reasons behind this decision. decision.
1. Routers may want to track per-host membership status on an 1. Routers may want to track per-host membership status on an
interface. This allows routers to implement fast leaves (e.g., interface. This allows routers to implement fast leaves (e.g.,
for layered multicast congestion control schemes) as well as for layered multicast congestion control schemes) as well as
track membership status for possible accounting purposes. track membership status for possible accounting purposes.
2. Membership Report suppression does not work well on bridged LANs. 2. Membership Report suppression does not work well on bridged LANs.
Many bridges and Layer2/Layer3 switches that implement IGMP Many bridges and Layer 2 / Layer 3 switches that implement IGMP
snooping do not forward IGMP messages across LAN segments in snooping do not forward IGMP messages across LAN segments in
order to prevent membership report suppression. Removing order to prevent membership report suppression. Removing
membership report suppression eases the job of these IGMP membership report suppression eases the job of these IGMP
snooping devices. snooping devices.
3. By eliminating membership report suppression, hosts have fewer 3. By eliminating membership report suppression, hosts have fewer
messages to process; this leads to a simpler state machine messages to process; this leads to a simpler state machine
implementation. implementation.
4. In IGMPv3, a single membership report now bundles multiple 4. In IGMPv3, a single membership report now bundles multiple
multicast group records to decrease the number of packets sent. multicast group records to decrease the number of packets sent.
In comparison, the previous versions of IGMP required that each In comparison, the previous versions of IGMP required that each
multicast group be reported in a separate message. multicast group be reported in a separate message.
A.3. Switching Router Filter Modes from EXCLUDE to INCLUDE A.3. Switching Router Filter Modes from EXCLUDE to INCLUDE
If there exist hosts in both EXCLUDE and INCLUDE modes for a single If hosts exist in both EXCLUDE and INCLUDE modes for a single
multicast group in a network, the router must be in EXCLUDE mode as multicast group in a network, the router must be in EXCLUDE mode as
well (see Section 6.2.1). In EXCLUDE mode, a router forwards traffic well (see Section 6.2.1). In EXCLUDE mode, a router forwards traffic
from all sources unless that source exists in the exclusion source from all sources unless that source exists in the exclusion source
list. If all hosts in EXCLUDE mode cease to exist, it would be list. If all hosts in EXCLUDE mode cease to exist, it would be
desirable for the router to switch back to INCLUDE mode seamlessly desirable for the router to switch back to INCLUDE mode seamlessly
without interrupting the flow of traffic to existing receivers. without interrupting the flow of traffic to existing receivers.
One of the ways to accomplish this is for routers to keep track of One of the ways to accomplish this is for routers to keep track of
all sources desired by hosts that are in INCLUDE mode even though the all sources desired by hosts that are in INCLUDE mode even though the
router itself is in EXCLUDE mode. If the group timer now expires in router itself is in EXCLUDE mode. If the group timer now expires in
EXCLUDE mode, it implies that there are no hosts in EXCLUDE mode on EXCLUDE mode, it implies that there are no hosts in EXCLUDE mode on
the network (otherwise a membership report from that host would have the network (otherwise, a membership report from that host would have
refreshed the group timer). The router can then switch to INCLUDE refreshed the group timer). The router can then switch to INCLUDE
mode seamlessly with the list of sources currently being forwarded in mode seamlessly with the list of sources currently being forwarded in
its source list. its source list.
Appendix B. Summary of Changes from IGMPv2 Appendix B. Summary of Changes from IGMPv2
While the main additional feature of IGMPv3 is the addition of source While the main additional feature of IGMPv3 is the addition of source
filtering, the following is a summary of other changes from RFC 2236. filtering, the following is a summary of other changes from
[RFC2236].
* State is maintained as Group + List-of-Sources, not simply Group * State is maintained as Group + List-of-Sources, not simply Group
as in IGMPv2. as in IGMPv2.
* Interoperability with IGMPv1 and IGMPv2 systems is defined as * Interoperability with IGMPv1 and IGMPv2 systems is defined as
operations on the IGMPv3 state. operations on the IGMPv3 state.
* The IP Service Interface has changed to allow specification of * The IP service interface has changed, to allow specification of
source-lists. source-lists.
* The Querier includes its Robustness Variable and Query Interval in * The Querier includes its Robustness Variable and Query Interval in
Query packets to allow synchronization of these variables on non- Query packets to allow synchronization of these variables on non-
Queriers. Queriers.
* The Max Response Time in Query messages has an exponential range, * The Max Response Time in Query messages has an exponential range,
changing the maximum from 25.5 seconds to about 53 minutes, for changing the maximum from 25.5 seconds to about 53 minutes, for
use on links with huge numbers of systems. use on links with a huge number of systems.
* Hosts retransmit state-change messages for increased robustness. * Hosts retransmit state-change messages for increased robustness.
* Additional data sections are defined to allow later extensions. * Additional data sections are defined, to allow later extensions.
* Report packets are sent to 224.0.0.22, to assist layer-2 switches * Report packets are sent to 224.0.0.22, to assist Layer 2 switches
in snooping. in snooping.
* Report packets can contain multiple group records, to allow * Report packets can contain multiple group records, to allow
reporting of full current state using fewer packets. reporting of full current state using fewer packets.
* Hosts no longer perform suppression, to simplify implementations * Hosts no longer perform suppression, to simplify implementations
and permit explicit membership tracking. and permit explicit membership tracking.
* New Suppress Router-Side Processing (S) flag in Query messages * A new S flag in Query messages fixes robustness issues, which were
fixes robustness issues which were also present in IGMPv2. also present in IGMPv2.
Appendix C. Summary of Changes from RFC 3376 Appendix C. Summary of Changes from RFC 3376
The following is a list of changes made since RFC 3376. The following is a list of changes made since [RFC3376] was
published.
* Modified definition of Older Version Querier Present Interval to * Modified the definition of Older Version Querier Present Interval
address Erratum 4375. to address Erratum 4375.
* Modified metadata to fix Obsoletes vs Updates relationship with * Modified the metadata to fix the Obsoletes vs. Updates
RFC 2236 per Erratum 1501. relationship with [RFC2236] per Erratum 1501.
* Updated introductory text to describe Updates relationship with * Updated the introductory text to describe the Updates relationship
RFC 2236 per Erratum 7339. with [RFC2236] per Erratum 7339.
* Updated Group Membership Interval definition to address Erratum * Updated the definition of Group Membership Interval to address
6725. Erratum 6725.
* Updated text for Router Filter-Mode to address Erratum 5562. * Updated the text relating to the router filter-mode to address
Erratum 5562.
* Clarified the use of General Queries in the Querier election * Clarified the use of General Queries in the Querier election
process. process.
Acknowledgments
We would like to thank Ran Atkinson, Luis Costa, Toerless Eckert,
Dino Farinacci, Serge Fdida, Wilbert de Graaf, Sumit Gupta, Mark
Handley, Bob Quinn, Michael Speer, Dave Thaler, and Rolland Vida for
comments and suggestions on [RFC3376].
Stig Venaas, Hitoshi Asaeda, and Mike McBride have provided valuable
feedback on this specification, and we thank them for their input.
Contributors
Brad Cain, Steve Deering, Isidor Kouvelas, Bill Fenner, and Ajit
Thyagarajan are the authors of [RFC3376], which forms the bulk of the
content contained herein.
Anuj Budhiraja, Toerless Eckert, Olufemi Komolafe, and Tim Winters
have contributed valuable content to this specification.
Author's Address Author's Address
Brian Haberman (editor) Brian Haberman (editor)
Johns Hopkins University Applied Physics Lab Johns Hopkins University Applied Physics Lab
Email: brian@innovationslab.net Email: brian@innovationslab.net
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