Dell FCX624-I Laptop User Manual


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770 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
IGMP V3
25
IGMP V3
The Internet Group Management Protocol (IGMP) allows an IPV4 interface 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. This release introduces the support of IGMP
version 3 (IGMP V3) on Layer 3 Switches.
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 queries
determine if any interface wants to receive traffic from the router. The queries include the IP
address of the traffic source (S) or the ID of the multicast group (G, or both).
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:
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 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.
In response to membership reports from the interfaces, the router sends a Group-Specific or a
Group-and-Source Specific query to the multicast interfaces. Each query is sent three times with a
one-second interval in between each transmission to ensure the interfaces receive the query. For
example, a router receives a membership report with a Source-List-Change record to block old
sources from an interface. The router sends Group-and-Source Specific Queries to the source and
group (S,G) identified in the record. If none of the interfaces is interested in the (S,G), it is removed
from (S,G) list for that interface on the router.
Each IGMP V3-enabled router maintains a record of the state of each group and each physical port
within a virtual routing interface. This record contains the group, group-timer, filter mode, and
source records information for the group or interface. Source records contain information on the
source address of the packet and source timer. If the source timer expires when the state of the
group or interface is in Include mode, the record is removed.