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Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
OL-12247-01
Chapter 44 Configuring IP Multicast Routing
Configuring Optional IGMP Features
The switch elects a PIM designated router (DR) for the LAN (subnet). The DR is the router or multilayer
switch with the highest IP address for IGMPv2. For IGMPv1, the DR is elected according to the
multicast routing protocol that runs on the LAN. The designated router is responsible for sending IGMP
host-query messages to all hosts on the LAN. In sparse mode, the designated router also sends PIM
register and PIM join messages toward the RP router.
Beginning in privileged EXEC mode, follow these steps to modify the host-query interval. This
procedure is optional.
To return to the default setting, use the no ip igmp query-interval interface configuration command.
Changing the IGMP Query Timeout for IGMPv2
If you are using IGMPv2, you can specify the period of time before the switch takes over as the querier
for the interface. By default, the switch waits twice the query interval controlled by the ip igmp
query-interval interface configuration command. After that time, if the switch has received no queries,
it becomes the querier.
You can configure the query interval by entering the show ip igmp interface interface-id privileged
EXEC command.
Beginning in privileged EXEC mode, follow these steps to change the IGMP query timeout. This
procedure is optional.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the interface to be configured, and enter interface configuration
mode.
Step 3
ip igmp query-interval seconds
Configure the frequency at which the designated router sends IGMP
host-query messages.
By default, the designated router sends IGMP host-query messages
every 60 seconds to keep the IGMP overhead very low on hosts and
networks. The range is 1 to 65535.
Step 4
end
Return to privileged EXEC mode.
Step 5
show ip igmp interface [interface-id]
Verify your entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the interface to be configured, and enter interface configuration
mode.
Step 3
ip igmp querier-timeout seconds
Specify the IGMP query timeout.
The default is 60 seconds (twice the query interval). The range is 60
to 300.
Step 4
end
Return to privileged EXEC mode.