Cisco Systems 78-11741-02 Changing the Igmp Query Timeout, IPC-413, Routerconfig-if# ip igmp

Configuring IP Multicast Routing

IGMP Features Configuration Task List

If IGMPv3 is needed to support SSM, then you have two configuration alternatives as follows:

•Configure only the interface for IGMPv2 and use IGMP v3lite and URD.

•Enable IGMPv3 and accept the higher leave latencies through the CGMP switch.

Changing the IGMP Query Timeout

You can specify the period of time before the router takes over as the querier for the interface, after the previous querier has stopped doing so. By default, the router waits two times the query interval controlled by the ip igmp query-intervalinterface configuration command. After that time, if the router has received no queries, it becomes the querier. This feature requires IGMP Version 2.

To change the query timeout, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip igmp query-timeout seconds	Sets the IGMP query timeout.

Changing the Maximum Query Response Time

By default, the maximum query response time advertised in IGMP queries is 10 seconds. If the router is using IGMP Version 2, you can change this value. The maximum query response time allows a router to quickly detect that there are no more directly connected group members on a LAN. Decreasing the value allows the router to prune groups faster.

To change the maximum query response time, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# ip igmp	Sets the maximum query response time advertised in IGMP queries.
query-max-response-time seconds

Configuring the Router as a Statically Connected Member

Sometimes either there is no group member on a network segment or a host cannot report its group membership using IGMP. However, you may want multicast traffic to go to that network segment. The following are two ways to pull multicast traffic down to a network segment:

•Use the ip igmp join-groupinterface configuration command. With this method, the router accepts the multicast packets in addition to forwarding them. Accepting the multicast packets prevents the router from fast switching.

•Use the ip igmp static-groupinterface configuration command. With this method, the router does not accept the packets itself, but only forwards them. Hence, this method allows fast switching. The outgoing interface appears in the IGMP cache, but the router itself is not a member, as evidenced by lack of an “L” (local) flag in the multicast route entry.

To configure the router itself to be a statically connected member of a group (and allow fast switching), use the following command in interface configuration mode:

Cisco IOS IP Configuration Guide

IPC-413