1142 Multicast CommandsDefault ConfigurationThis command has no default configuration.Command ModeGlobal Configuration modeUser GuidelinesUse of a multicast routing protocol is recommended (e.g., PIM, when ipmulticast is enabled).Unless required, IGMP/MLD snooping should be disabled when ip multicastis enabled. If a multicast source is connected to a VLAN on which both L3multicast and IGMP/MLD snooping are enabled, the multicast source isforwarded to the mrouter ports that have been discovered when the multicastsource is first seen. If a new mrouter is later discovered on a different port, themulticast source data is not forwarded to the new port. Likewise, if an existingmrouter times out or stops querying, the multicast source data continues tobe forwarded to that port. If a host in the VLAN subsequently joins or leavesthe group, the list of mrouter ports is updated for the multicast source andthe forwarding of the multicast source is adjusted. The workaround to thislimitation is to statically configure mrouter ports when enabling IGMP/MLDsnooping in L3 multicast enabled VLANs.This command is not affected by enabling/disabling PIM or DVMRP.This command enables both ipv4 and ipv6 multicast routing.ExampleThe following example enables IP multicast on the router.console#configureconsole(config)#ip multicastip multicast ttl-thresholdUse the ip multicast ttl-threshold command in Interface VLANConfiguration mode to apply attlvalue to a routing interface.ttlvalue is theTTL threshold which is applied to the multicast Data packets forwardedthrough the interface.
