Administrator Guide

Layer 3 Routing Commands 1661
Default Configuration
This command has no default configuration.
Command Mode
Global Configuration mode
User Guidelines
Use of a multicast routing protocol is recommended (e.g., PIM) when ip
multicast is enabled.
Unless required, IGMP/MLD snooping should be disabled when ip multicast
is enabled. If a multicast source is connected to a VLAN on which both L3
multicast and IGMP/MLD snooping are enabled, the multicast source is
forwarded to the mrouter ports that have been discovered when the multicast
source is first seen. If a new mrouter is later discovered on a different port, the
multicast source data is not forwarded to the new port. Likewise, if an existing
mrouter times out or stops querying, the multicast source data continues to
be forwarded to that port. If a host in the VLAN subsequently joins or leaves
the group, the list of mrouter ports is updated for the multicast source and
the forwarding of the multicast source is adjusted. The workaround to this
limitation is to statically configure mrouter ports when enabling IGMP/MLD
snooping 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.
Example
The following example enables IP multicast on the router.
console#configure
console(config)#ip multicast
ip multicast ttl-threshold
Use the ip multicast ttl-threshold command in Interface VLAN
Configuration mode to apply a
ttlvalue to a routing interface. ttlvalue is the
TTL threshold which is applied to the multicast Data packets forwarded
through the interface.
2CSNXXX_SWUM204.book Page 1661 Monday, January 25, 2016 1:25 PM