Internet Engineering Task Force (IETF) H. Liu

Internet Engineering Task Force (IETF) H. Liu
Request for Comments: 5790 W. Cao
Category: Standards Track Huawei Technologies
ISSN: 2070-1721 H. Asaeda
Keio University
February 2010

Lightweight Internet Group Management Protocol Version 3 (IGMPv3) and
Multicast Listener Discovery Version 2 (MLDv2) Protocols

Abstract

This document describes lightweight IGMPv3 and MLDv2 protocols (LW-
IGMPv3 and LW-MLDv2), which simplify the standard (full) versions of
IGMPv3 and MLDv2. The interoperability with the full versions and
the previous versions of IGMP and MLD is also taken into account.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5790.

Copyright Notice

Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Liu, et al. Standards Track [Page 1]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
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not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.

Table of Contents

1. Introduction ....................................................3
2. Terminology .....................................................4
3. Simplification Method Overview ..................................4
3.1. Behavior of Group Members ..................................5
3.2. Behavior of Multicast Routers ..............................5
4. LW-IGMPv3 Protocol for Group Members ............................6
4.1. Query and Report Messages ..................................6
4.2. Action on Change of Interface State ........................6
4.3. Action on Reception of a Query .............................7
4.4. LW-IGMPv3 Group Record Types ...............................7
5. LW-IGMPv3 Protocol for Multicast Routers ........................9
5.1. Group Timers and Source Timers in the Lightweight Version ..9
5.2. Source-Specific Forwarding Rules ..........................10
5.3. Reception of Current-State Records ........................10
5.4. Reception of Source-List-Change and
Filter-Mode-Change Records ................................12
6. Interoperability ...............................................13
6.1. Interoperation with the Full Version of IGMPv3/MLDv2 ......13
6.1.1. Behavior of Group Members ..........................13
6.1.2. Behavior of Multicast Routers ......................13
6.2. Interoperation with IGMPv1/IGMPv2 .........................14
6.2.1. Behavior of Group Members ..........................14
6.2.2. Behavior of Multicast Routers ......................14
6.3. Interoperation with MLDv1 .................................15
7. Implementation Considerations ..................................15
7.1. Implementation of Source-Specific Multicast ...............15
7.2. Implementation of Multicast Source Filter (MSF) APIs ......16
8. Security Considerations ........................................16
9. Acknowledgements ...............................................16
10. References ....................................................16
10.1. Normative References .....................................16
10.2. Informative References ...................................17

Liu, et al. Standards Track [Page 2]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

1. Introduction

IGMP version 3 [2] and MLD version 2 [3] implement source filtering
capabilities that are not supported by their earlier versions, IGMPv1
[4], IGMPv2 [5], and MLDv1 [6]. An IGMPv3- or MLDv2-capable host can
tell its upstream router which group it would like to join by
specifying which sources it does or does not intend to receive
multicast traffic from. IGMPv3 and MLDv2 add the capability for a
multicast router to learn sources that are of interest or that are
not of interest for a particular multicast address. This information
is used during forwarding of multicast data packets.

INCLUDE and EXCLUDE filter-modes are introduced to support the source
filtering function. If a host wants to receive from specific
sources, it sends an IGMPv3 or MLDv2 report with filter-mode set to
INCLUDE. If the host does not want to receive from some sources, it
sends a report with filter-mode set to EXCLUDE. A source-list for
the given sources shall be included in the Report message.

INCLUDE and EXCLUDE filter-modes are also defined in a multicast
router to process the IGMPv3 or MLDv2 reports. When a multicast
router receives the Report messages from its downstream hosts, it
forwards the corresponding multicast traffic by managing requested
group and source addresses. Group timers and source timers are used
to maintain the forwarding state of desired groups and sources under
certain filter-modes. When a group report arrives or a certain timer
expires, a multicast router may update the desired or undesired
source-lists, reset related timer values, change filter-mode, or
trigger group queries. With all of the above factors correlating
with each other, the determination rules become relatively complex,
as the interface states could be frequently changed.

The multicast filter-mode improves the ability of the multicast
receiver to express its desires. It is useful to support Source-
Specific Multicast (SSM) [7] by specifying interesting source
addresses with INCLUDE mode. However, practical applications do not
use EXCLUDE mode to block sources very often, because a user or
application usually wants to specify desired source addresses, not
undesired source addresses. Even if a user explicitly refuses
traffic from some sources in a group, when other users in the same
shared network have an interest in these sources, the corresponding
multicast traffic will still be forwarded to the network. It is
generally unnecessary to support the filtering function that blocks
sources.

This document proposes simplified versions of IGMPv3 and MLDv2, named
Lightweight IGMPv3 and Lightweight MLDv2 (or LW-IGMPv3 and LW-MLDv2).
LW-IGMPv3 and LW-MLDv2 are subsets of the standard IGMPv3 and MLDv2.

Liu, et al. Standards Track [Page 3]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

They support both Any-Source Multicast (ASM) and SSM communications
without a filtering function that blocks sources. Not only are they
compatible with the standard IGMPv3 and MLDv2, but also the protocol
operations made by hosts and routers (or switches performing IGMPv3/
MLDv2 snooping) are simplified to reduce the complicated operations.
Since LW-IGMPv3 and LW-MLDv2 are fully compatible with IGMPv3 and
MLDv2, hosts or routers that have implemented the full version do not
need to implement or modify anything to cooperate with LW-IGMPv3/
LW-MLDv2 hosts or routers.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [1].

In addition, the following terms are used in this document.

(*,G) join:
An operation triggered by a host that wants to join a group G. In
this case, the host receives from all sources sending to group G.
This is typical in ASM communication.

(S,G) join:
An operation triggered by a host that wants to join a group G,
specifying a desired source S. In this case, the host receives
traffic only from source S sending to group G.

INCLUDE (S,G) join:
An operation triggered by a host that wants to join a group G under
INCLUDE filter-mode, specifying a desired source S. Same meaning as
(S,G) join.

EXCLUDE (*,G) join:
An operation triggered by a host that wants to join a group G under
EXCLUDE filter-mode. Same meaning as (*,G) join.

EXCLUDE (S,G) join:
An operation triggered by a host that wants to join a group G under
EXCLUDE filter-mode, specifying an undesired source S. This
operation is not supported by LW-IGMPv3/LW-MLDv2.

3. Simplification Method Overview

The principle is to simplify the host's and router's behavior as much
as possible to improve efficiency, while guaranteeing
interoperability with the full versions, and introducing no side
effects on applications.

Liu, et al. Standards Track [Page 4]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

For convenience, this document mainly discusses IGMPv3, since MLDv2
inherits the same source filtering mechanism, but this document
additionally shows MLDv2's unique specifications when needed.

3.1. Behavior of Group Members

LW-IGMPv3 inherits the service interface model of IGMPv3.

IPMulticastListen ( socket, interface, multicast-address,
filter-mode, source-list )

In the lightweight protocol, INCLUDE mode on the host part has the
same usage as the full version for INCLUDE (S,G) join, while EXCLUDE
mode on the host part is preserved only for excluding null source-
lists, which denotes a (*,G) join as used by IGMPv2/IGMPv1/MLDv1.
The detailed host operation of LW-IGMPv3/LW-MLDv2 is described in
Section 4.

3.2. Behavior of Multicast Routers

In IGMPv3, router filter-mode is defined to optimize the state
description of a group membership [2]. As a rule, once a member
report is in EXCLUDE mode, the router filter-mode for the group will
be set to EXCLUDE. When all systems cease sending EXCLUDE mode
reports, the filter-mode for that group may transit back to INCLUDE
mode. The group timer is used to identify such a transition.

In LW-IGMPv3, hosts primarily send INCLUDE requests, and also can
request an EXCLUDE (*,G) join, which can be interpreted by the router
as a request to include all sources. Without the more general form
of EXCLUDE requests, it is unnecessary for the router to maintain the
EXCLUDE filter-mode, and the state model for multicast routers can be
simplified as:

(multicast address, group timer, (source records))

Here a group timer is kept to represent a (*,G) join. Its basic
behavior is: when a router receives a (*,G) join, it will set its
group timer and keep the source-list for sources specified in the
previously received source records. When the group timer expires,
the router may change to reception of the listed sources only. The
definition of the source record is the same as in the full version.

The elimination of the filter-mode will greatly simplify the router
behavior. The details of router operation are described in
Section 5.

Liu, et al. Standards Track [Page 5]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

4. LW-IGMPv3 Protocol for Group Members

4.1. Query and Report Messages

LW-IGMPv3 uses the same two sets of messages, Query and Report
messages, as the full version protocols. There is no difference
between the definition and usage of the Query message. But the
report types in lightweight protocols are reduced because an
operation that triggers EXCLUDE (S,G) join is omitted.

There are three Group Record Types defined in the full IGMPv3: the
Current-State Record denoted by MODE_IS_INCLUDE (referred to as
IS_IN) or MODE_IS_EXCLUDE (IS_EX), the Filter-Mode-Change Record
denoted by CHANGE_TO_INCLUDE_MODE (TO_IN) or CHANGE_TO_EXCLUDE_MODE
(TO_EX), and the Source-List-Change Record denoted by
ALLOW_NEW_SOURCES (ALLOW) or BLOCK_OLD_SOURCES (BLOCK). LW-IGMPv3
inherits the actions on change of interface state and on reception of
a query, but the IS_IN and IS_EX record types are eliminated and
Current-State Records are replaced by other records. The following
sections explain the details.

4.2. Action on Change of Interface State

When the state of an interface of a group member host is changed, a
State-Change Report for that interface is immediately transmitted
from that interface. The type and contents of the Group Record(s) in
that report are determined by comparing the filter-mode and source-
list for the affected multicast address before and after the change.
While the requirements for the computation are the same as for the
full version, in a lightweight version host the interface state
change rules are simplified due to the reduction of message types.
The contents of the new transmitted report are calculated as follows
(Group Record Types are described in Section 4.4):

Old State New State State-Change Report Sent
----------- ----------- ------------------------

INCLUDE (A) INCLUDE (B) ALLOW(B-A), BLOCK(A-B)

INCLUDE (A) EXCLUDE ({}) TO_EX({})

INCLUDE ({}) EXCLUDE ({}) TO_EX({})

EXCLUDE ({}) INCLUDE (B) TO_IN(B)

Liu, et al. Standards Track [Page 6]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

As in the full version, to cover the possibility of the State-Change
Report being missed by one or more multicast routers, it is
retransmitted [Robustness Variable]-1 more times, at intervals chosen
at random from the range (0, [Unsolicited Report Interval]). (These
values are defined in [2][3].)

4.3. Action on Reception of a Query

As in the full version, when a lightweight version host receives a
query, it does not respond immediately. 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 received Query message
[2][3]. The system may receive a variety of queries on different
interfaces and of different kinds (e.g., General Queries, Group-
Specific Queries, and Group-and-Source-Specific Queries), each of
which may require its own delayed response.

Before scheduling a response to a query, the system must first
consider previously scheduled pending responses and in many cases
schedule a combined response. Therefore, the lightweight version
host must be able to maintain the following state:

o A timer per interface for scheduling responses to General Queries.

o A per-group and interface timer for scheduling responses to Group-
Specific and Group-and-Source-Specific Queries.

o A per-group and interface list of sources to be reported in the
response to a Group-and-Source-Specific Query.

LW-IGMPv3 inherits the full version's rules that are used to
determine if a report needs to be scheduled. The difference is
regarding the simplification of EXCLUDE filter-mode and the type of
report as detailed in Section 4.4.

4.4. LW-IGMPv3 Group Record Types

Among the Group Record Types defined in the full IGMPv3, several
record types are not used in LW-IGMPv3 as some of the processes
related to the filter-mode change to the EXCLUDE mode are eliminated
and some of the Report messages are converged into a record having a
null source address list. All of the record types of Report messages
used by the full and lightweight version protocols are shown as
follows:

Liu, et al. Standards Track [Page 7]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

IGMPv3 LW-IGMPv3 Comments
--------- --------- -------------------------------------

IS_EX({}) TO_EX({}) Query response for (*,G) join

IS_EX(x) N/A Query response for EXCLUDE (x,G) join

IS_IN(x) ALLOW(x) Query response for INCLUDE (x,G) join

ALLOW(x) ALLOW(x) INCLUDE (x,G) join

BLOCK(x) BLOCK(x) INCLUDE (x,G) leave

TO_IN(x) TO_IN(x) Change to INCLUDE (x,G) join

TO_IN({}) TO_IN({}) (*,G) leave

TO_EX(x) N/A Change to EXCLUDE (x,G) join

TO_EX({}) TO_EX({}) (*,G) join

where "x" represents a non-null source address list and "({})"
represents a null source address list. For instance, IS_EX({}) means
a report whose record type is IS_EX with a null source address list.
"N/A" represents not applicable (or no use) because the corresponding
operation should not occur in the lightweight version protocols.

LW-IGMPv3 does not use EXCLUDE filter-mode with a non-null source
address list. A multicast router creates the same state when it
receives a Report message containing either IS_EX({}) or TO_EX({})
record types. Therefore, LW-IGMPv3 integrates the IS_EX({})
operation with the TO_EX({}) operation.

When an LW-IGMPv3 host needs to make a query response for the state
of INCLUDE (x,G) join, it makes a response whose message type is
expressed with ALLOW(x), instead of using the IS_IN record type.
Because the router's processing of the two messages is exactly the
same, the IS_IN(x) type is eliminated for simplification.

An LW-IGMPv3 host does not use EXCLUDE mode, while TO_IN and TO_EX
records are used for example in the following situation: the host
first launches an application (AP1) that requests INCLUDE (x,G) join,
and sends ALLOW(x). Then the host launches another application (AP2)
that joins (*,G), and it sends TO_EX({}). In this condition, when
AP2 terminates but AP1 keeps working on the lightweight version host,
the host sends a report with TO_IN(x) record type for [Robustness
Variable] times.

Liu, et al. Standards Track [Page 8]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

Although an LW-IGMPv3 host adopts the four message types (ALLOW,
BLOCK, TO_IN, and TO_EX) for simplification, using IS_EX({}) and
IS_IN(x) (respectively, instead of TO_EX({}) and ALLOW(x)) in
response to queries is not inhibited. This will not introduce the
interoperation problem because the router process is, respectively,
the same for the mentioned two message set, as long as the router
implementation follows the rules given by full IGMPv3.

5. LW-IGMPv3 Protocol for Multicast Routers

The major difference between the full and lightweight version
protocols on the router part is that in the lightweight version
filter-mode is discarded and the function of the group timer is
redefined. The states maintained by the lightweight router are
reduced and the protocol operation is greatly simplified.

5.1. Group Timers and Source Timers in the Lightweight Version

In lightweight and full IGMPv3 routers, a source timer is kept for
each source record and it is updated when the source is present in a
received report. It indicates the validity of the source and needs
to be referred to when the router takes its forwarding decision.

The group timer being used in the full version of IGMPv3 for
transitioning the router's filter-mode from EXCLUDE to INCLUDE is
redefined in the lightweight protocols to identify the non-source-
specific receiving state maintained for (*,G) join. Once a group
record of TO_EX({}) is received, the group timer is set to represent
this (*,G) group join. The expiration of the group timer indicates
that there are no more listeners on the attached network for this
(*,G) group. Then if at this moment there are unexpired sources
(whose source timers are greater than zero), the router will change
to receiving traffic for those sources only. The role of the group
timer can be summarized as follows:

Group Timer Value Actions/Comments
------------------ --------------------------------------

G_Timer > 0 All members in this group.

G_Timer == 0 No more listeners to this (*,G) group.
If all source timers have expired, then
delete group record. If there are
still source record timers running,
use those source records with running
timers as the source record state.

Liu, et al. Standards Track [Page 9]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

The operation related to the group and source timers has some
differences compared to the full IGMPv3. In the full version, if a
source timer expires under the EXCLUDE router filter-mode, its
corresponding source record is not deleted until the group timer
expires for indicating undesired sources. In the lightweight
version, since there is no need to keep such records for blocking
specific sources, if a source timer expires, its source record should
be deleted immediately, not waiting for the time-out of the group
timer.

5.2. Source-Specific Forwarding Rules

A full version multicast router needs to consult IGMPv3 state
information when it makes decisions on forwarding a datagram from a
source, based on the router filter-mode and source timer. In LW-
IGMPv3, because of the absence of the router filter-mode, the group
timer and source timer could be used for such decisions. The
forwarding suggestion made by LW-IGMPv3 to the routing protocols is
summarized as follows:

Group Timer Source Timer Action
------------ ------------------ -----------------------

G_Timer == 0 S_Timer > 0 Suggest forwarding
traffic from source

G_Timer == 0 S_Timer == 0 Suggest stopping
forwarding traffic from
source and remove
source record. If there
are no more source
records for the group,
delete group record

G_Timer == 0 No Source Elements Suggest not forwarding
traffic from source

G_Timer > 0 S_Timer >= 0 Suggest forwarding
traffic from source

G_Timer > 0 No Source Elements Suggest forwarding
traffic from source

5.3. Reception of Current-State Records

When receiving Current-State Records, the LW-IGMPv3 router resets its
group or source timers and updates its source-list within the group.
For source-specific group reception state (when G_Timer == 0 and

Liu, et al. Standards Track [Page 10]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

S_Timer > 0), the source-list contains sources whose traffic will be
forwarded by the router, while in non-source-specific group reception
(when G_Timer > 0), the source-list remembers the valid sources to
receive traffic from after toggling to source-specific reception
state.

Although the LW-IGMPv3 host only sends a subset of the messages of
the full version, the LW-IGMPv3 router should be able to process as
many messages as possible to be compatible with the full version
host. Note that if the report type is IS_EX(x) with a non-empty
source-list, the router will treat it as the same type of report with
an empty source-list. The following table describes the action taken
by a multicast router after receiving Current-State Records. The
notations have the same meaning as those in the full IGMPv3 protocol.

Old New
Source- Source-
Group Timer List Report Rec'd List Actions
------------ ------ ------------ ------ -----------

G_Timer == 0 A IS_IN(B) A+B (B)=GMI

G_Timer == 0 A IS_EX({}) A G_Timer=GMI

G_Timer > 0 A IS_IN(B) A+B (B)=GMI

G_Timer > 0 A IS_EX({}) A G_Timer=GMI

The above table could be further simplified since the processes are
exactly the same for the two values of the G_Timer:

Old New
Source- Source-
List Report Rec'd List Actions
------ ------------ ------ -----------

A IS_IN(B) A+B (B)=GMI

A IS_EX({}) A G_Timer=GMI

Without EXCLUDE filter-mode, a router's process on receiving a
Current-State Record is simple: when a router receives an IS_IN
report, it appends the reported source addresses to the previous
source-list with their source timers set to GMI. Upon receiving an
IS_EX({}) report, the router sets the non-source-specific receiving
states by resetting the group timer value and keeps the previous
source-list without modification.

Liu, et al. Standards Track [Page 11]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

5.4. Reception of Source-List-Change and Filter-Mode-Change Records

On receiving Source-List-Change and Filter-Mode-Change Records, the
LW-IGMPv3 router needs to reset its group and source timers, update
its source-list within the group, or trigger group queries. The
queries are sent by the router for the sources that are requested to
be no longer forwarded to a group. Note that if the report type is
TO_EX(x) with a non-empty source-list, the router will treat it as
the same type of report with an empty source-list. The table below
describes the state change and the actions that should be taken.

Old New
Source- Source-
Group Timer List Report Rec'd List Actions
------------ ------ ------------ ------ -------------

G_Timer == 0 A ALLOW(B) A+B (B)=GMI

G_Timer == 0 A BLOCK(B) A Send Q(G,A*B)

G_Timer == 0 A TO_IN(B) A+B (B)=GMI
Send Q(G,A-B)

G_Timer == 0 A TO_EX({}) A G_Timer=GMI

G_Timer > 0 A ALLOW(B) A+B (B)=GMI

G_Timer > 0 A BLOCK(B) A Send Q(G,A*B)

G_Timer > 0 A TO_IN(B) A+B (B)=GMI
SendQ(G,A-B)
Send Q(G)

G_Timer > 0 A TO_EX({}) A G_Timer=GMI

The table could be further simplified by merging duplicate lines:

Liu, et al. Standards Track [Page 12]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

Old New
Source- Source-
List Report Rec'd List Actions
------ ------------ ------ ----------------------

A ALLOW(B) A+B (B)=GMI

A BLOCK(B) A Send Q(G,A*B)

A TO_IN(B) A+B (B)=GMI
Send Q(G,A-B)
If G_Timer>0 Send Q(G)

A TO_EX({}) A G_Timer=GMI

6. Interoperability

LW-IGMPv3/LW-MLDv2 hosts and routers must interoperate with hosts and
routers of the full version [2][3]. Also, LW-IGMPv3/LW-MLDv2 hosts
and routers must interoperate gracefully with hosts and routers
running IGMPv1/v2 or MLDv1.

6.1. Interoperation with the Full Version of IGMPv3/MLDv2

LW-IGMPv3/LW-MLDv2 do not introduce any change on the message formats
of the group Query and Report messages that the full version
protocols use.

6.1.1. Behavior of Group Members

An LW-IGMPv3 host's compatibility mode is determined from the Host
Compatibility Mode variable, which can be in one of three states:
IGMPv1, IGMPv2, or IGMPv3. When a lightweight host behaves on its
interface as LW-IGMPv3, its Host Compatibility Mode of that interface
is set to IGMPv3, and the host sends a subset of IGMPv3 Report
messages, which can be recognized by a multicast router running the
full or the lightweight IGMPv3 protocol on the same LAN.

6.1.2. Behavior of Multicast Routers

An LW-IGMPv3 or LW-MLDv2 router does not process directly IS_EX(x)
and TO_EX(x) reports that are used by the full version. When an LW-
IGMPv3/LW-MLDv2 router receives these Report messages from full
version hosts, it MUST translate them internally to IS_EX({}) and
TO_EX({}) respectively and behave accordingly.

Liu, et al. Standards Track [Page 13]

RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

6.2. Interoperation with IGMPv1/IGMPv2

Since the lightweight protocols can be treated as a parallel version
of the full version of IGMPv3/MLDv2, its compatibility principle and
method with the older version are generally the same as that of full
IGMPv3/MLDv2.

6.2.1. Behavior of Group Members

The Host Compatibility Mode of an interface is set to IGMPv2 and its
IGMPv2 Querier Present timer is set to Older Version Querier Present
Timeout seconds (defined in [2]) whenever an IGMPv2 General Query is
received on that interface. The Host Compatibility Mode of an
interface is set to IGMPv1 and its IGMPv1 Querier Present timer is
set to Older Version Querier Present Timeout seconds whenever an
IGMPv1 Membership Query is received on that interface.

In the presence of older version group members, LW-IGMPv3 hosts may
allow its Report message to be suppressed by either an IGMPv1 or
IGMPv2 membership report. However, because the transmission of
IGMPv1 or v2 packets reduces the capability of the LW-IGMPv3 system,
as a potential protection mechanism, the choice to enable or disable
the use of backward compatibility may be configurable.

6.2.2. Behavior of Multicast Routers

The behavior of an LW-IGMPv3 router when placed on a network where
there are routers that have not been upgraded to IGMPv3 is exactly
the same as for a full IGMPv3 router in this situation [2].

A full IGMPv3 router uses Group Compatibility Mode (whose value is
either of IGMPv1, IGMPv2, or IGMPv3) per group record to indicate
which version of IGMP protocol it applies to the group. This value
is set according to the version of the received IGMP reports. When
Group Compatibility Mode is IGMPv3, the lightweight router performs
the LW-IGMPv3 protocol for that group.

When Group Compatibility Mode is IGMPv2, an LW-IGMPv3 router inherits
this compatibility mechanism with the following rules:

IGMP Message LW-IGMPv3 Equivalent
-------------- --------------------

v2 Report TO_EX({})

v2 Leave TO_IN({})

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RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

When Group Compatibility Mode is IGMPv1, an LW-IGMPv3 router
internally translates the following IGMPv1 and IGMPv2 messages for
that group to their LW-IGMPv3 equivalents:

IGMP Message LW-IGMPv3 Equivalent
-------------- --------------------

v1 Report TO_EX({})

v2 Report TO_EX({})

6.3. Interoperation with MLDv1

LW-MLDv2 hosts and routers MUST interoperate with hosts and routers
running MLDv1. The method is the same as described in Section 6.2.
The difference is that when an LW-MLDv2 router has a MLDv1 listener
on its network, it translates the following MLDv1 messages to their
LW-MLDv2 equivalents:

MLDv1 Message LW-MLDv2 Equivalent
------------- -------------------

Report TO_EX({})

Done TO_IN({})

7. Implementation Considerations

The lightweight protocols require no additional procedure for the
implementation of the related protocols or systems, e.g., IGMP/MLD
snooping, multicast routing protocol, and operation of application
sockets, while the processing loads on the switches and routers that
run IGMPv3/MLDv2 (snooping) and multicast routing protocols may be
greatly decreased.

7.1. Implementation of Source-Specific Multicast

[8] specifies the requirements for the implementation of Source-
Specific Multicast (SSM) on IGMPv3/MLDv2 hosts and routers. The
lightweight protocol follows the same rules as given in [8] except
for the change of the message types due to the simplification.

An LW-IGMPv3/LW-MLDv2 host should not invoke (*,G) join (i.e.,
TO_EX({})) and (*,G) leave (i.e., TO_IN({})) for applications whose
multicast addresses are in the SSM address range. An upstream LW-
IGMPv3/LW-MLDv2 router MUST NOT establish forwarding state and MAY
log an error on reception of them as described in [7].

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RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

7.2. Implementation of Multicast Source Filter (MSF) APIs

[9] defines the following Multicast Source Filter (MSF) APIs: (1)
IPv4 Basic MSF APIs, (2) IPv4 Advanced MSF APIs, (3) Protocol-
Independent Basic MSF APIs, and (4) Protocol-Independent Advanced MSF
APIs.

According to the MSF API definition, an LW-IGMPv3 host should
implement either the IPv4 Basic MSF API or the Protocol-Independent
Basic MSF API, and an LW-MLDv2 host should implement the Protocol-
Independent Basic MSF API. Other APIs, IPv4 Advanced MSF API and
Protocol-Independent Advanced MSF API, are optional to implement in
an LW-IGMPv3/LW-MLDv2 host.

8. Security Considerations

The security considerations are the same as that of the full version
of IGMPv3/MLDv2.

9. Acknowledgements

The authors would like to thank MBONED and MAGMA working group
members. Special thanks is given to Marshall Eubanks, Guo Feng, Mark
Fine, Alfred Hoenes, Prashant Jhingran, Bharat Joshi, Guo Tao, Wang
Wendong, and Gong Xiangyang for their valuable suggestions and
comments on this document.

10. References

10.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.

[3] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
(MLDv2) for IPv6", RFC 3810, June 2004.

[4] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.

[5] Fenner, W., "Internet Group Management Protocol, Version 2",
RFC 2236, November 1997.

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RFC 5790 Lightweight IGMPv3 and MLDv2 February 2010

[6] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.

[7] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
RFC 4607, August 2006.

[8] Holbrook, H., Cain, B., and B. Haberman, "Using Internet Group
Management Protocol Version 3 (IGMPv3) and Multicast Listener
Discovery Protocol Version 2 (MLDv2) for Source-Specific
Multicast", RFC 4604, August 2006.

10.2. Informative References

[9] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
Extensions for Multicast Source Filters", RFC 3678,
January 2004.

Authors' Addresses

Hui Liu
Huawei Technologies Co., Ltd.
Huawei Bld., No.3 Xinxi Rd.
Shang-Di Information Industry Base
Hai-Dian Distinct, Beijing 100085
China

EMail: [email protected]

Wei Cao
Huawei Technologies Co., Ltd.
Huawei Bld., No.3 Xinxi Rd.
Shang-Di Information Industry Base
Hai-Dian Distinct, Beijing 100085
China

EMail: [email protected]

Hitoshi Asaeda
Keio University
Graduate School of Media and Governance
5322 Endo
Fujisawa, Kanagawa 252-8520
Japan

EMail: [email protected]

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