Dell PowerConnect B-RX Configuration Manual page 663

IGMP v3
The Internet Group Management Protocol (IGMP) allows an IPV4 system to communicate IP
Multicast group membership information to its neighboring routers. The routers in turn limit the
multicast of IP packets with multicast destination addresses to only those interfaces on the router
that are identified as IP Multicast group members.
In IGMP V2, when a router sent a query to the interfaces, the clients on the interfaces respond with
a membership report of multicast groups to the router. The router can then send traffic to these
groups, regardless of the traffic source. When an interface no longer needs to receive traffic from a
group, it sends a leave message to the router which in turn sends a group-specific query to that
interface to see if any other clients on the same interface is still active.
In contrast, IGMP V3 provides selective filtering of traffic based on traffic source. A router running
IGMP V3 sends queries to every multicast enabled interface at the specified interval. These general
queries determine if any interface wants to receive traffic from the router. The following are the
three variants of the Query message:
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The interfaces respond to these queries by sending a membership report that contains one or
more of the following records that are associated with a specific group:
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BigIron RX Series Configuration Guide
53-1002253-01
A "General Query" is sent by a multicast router to learn the complete multicast reception state
of the neighboring interfaces. In a General Query, both the Group Address field and the
Number of Sources (N) field are zero.
A "Group-Specific Query" is sent by a multicast router to learn the reception state, with respect
to a *single* multicast address, of the neighboring interfaces. In a Group-Specific Query, the
Group Address field contains the multicast address of interest, and the Number of Sources (N)
field contains zero.
A "Group-and-Source-Specific Query" is sent by a multicast router to learn if any neighboring
interface desires reception of packets sent to a specified multicast address, from any of a
specified list of sources. In a Group-and-Source-Specific Query, the Group Address field
contains the multicast address of interest, and the Source Address [i] fields contain the source
address(es) of interest.
Current-State Record that indicates from which sources the interface wants to receive and not
receive traffic. The record contains source address of interfaces and whether or not traffic will
be received or included (IS_IN) or not received or excluded (IS_EX) from that source.
Filter-mode-change record. If the interface changes its current state from IS_IN to IS_EX, a
TO_EX record is included in the membership report. Likewise, if an interface's current state
changes from IS_EX to IS_IN, a TO_IN record appears in the membership report.
IGMP V2 Leave report is equivalent to a TO_IN (empty) record in IGMP V3. This record means
that no traffic from this group will be received regardless of the source.
An IGMP V2 group report is equivalent to an IS_EX (empty) record in IGMP V3. This record
means that all traffic from this group will be received regardless of source.
Source-List-Change Record. If the interface wants to add or remove traffic sources from its
membership report, the membership report can have an ALLOW record, which contains a list
of new sources from which the interface wishes to receive traffic. It can also contains a BLOCK
record, which lists current traffic sources from which the interfaces wants to stop receiving
traffic.
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IGMP v3
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