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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring IP Multicast Routing
Configuring Optional IGMP Features
To return to the default setting, use the no ip igmp version interface configuration command.
Modifying the IGMP Host-Query Message Interval
The switch periodically sends IGMP host-query messages to discover which multicast groups are present
on attached networks. These messages are sent to the all-hosts multicast group (224.0.0.1) with a
time-to-live (TTL) of 1. The switch sends host-query messages to refresh its knowledge of memberships
present on the network. If, after some number of queries, the software discovers that no local hosts are
members of a multicast group, the software stops forwarding multicast packets to the local network from
remote origins for that group and sends a prune message upstream toward the source.
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.
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
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.
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