Chapter 4: Switching 65
1. The router sends a Host Membership query to 224.0.0.1 (all of the multicast
hosts on the subnet).
2. The host responds with a Host Membership Report for each group to which
it belongs, which is sent to the group address.
3. The switch intercepts the IGMP Membership report that was sent by the host
to join a particular multicast group.
4. The switch creates a multicast entry for that group and links it to the port on
which it has received the report and to all router ports.
5. The switch forwards the IGMP report to all router ports. The router receives
the IGMP report, and updates its multicast routing table accordingly.
6. To maintain group membership, the multicast router sends a IGMP query at
definite intervals. This query is intercepted by the switch, and is forwarded
to all ports on the switch. All hosts that are members of the group answer
that query.
7. The complementary message to join is the IGMP leave message. A host
sends a message to leave a group when it no longer desires to receive the
multicast services of that specific group.
8. Only one router per IP subnet sends queries. This router is called the query
router and is elected by the lowest IP address among the routers.
Defaults IGMP is disabled by default.
For more information on the IGMP snooping default values and commands, see
the CN1610 Network Switch CLI Command Reference.
CLI show
commands
You can use the following
show
commands in Privileged EXEC mode to view
information about the IGMP snooping feature:
Command Description
show igmpsnooping
Displays configuration information about IGMP
snooping.
show igmpsnooping
slot/port
Displays configuration information about IGMP
snooping interfaces.
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