Core Issue
The router should be configured with minimum configuration for either the Protocol Independent Multicast (PIM) dense mode or the PIM sparse mode, to ensure that multicast traffic is switched through the router.
Resolution
Perform these configurations to enable multicast routing on a router:
- Issue the ip multicast-routing command globally on the router.
- Enable PIM sparse or dense mode, by issuing the ip pim sparse-dense-mode command on all the multicast interfaces.
- In the case of sparse mode, a Rendezvous Point (RP) is to be configured. These are options to configure the RP in PIM sparse mode multicast networks:
- Configure a static RP address by issuing the ip pim rp-address <x.x.x.x> command. This method is not scalable, and is recommended only in very small, simple networks.
- Auto-RP utilizes the sparse-dense mode, which allows a group to be treated in sparse mode if an RP is known. If an RP is not known, then the group defaults to dense mode. RP information is conveyed to the routers by the Auto-RP mechanism, which uses two well known groups: 224.0.1.39 and 224.0.1.40. The advantage of this is that any change to the RP designation needs to be configured only on the RP routers, and not on the leaf routers, as in the static configuration.
For more information on configuring IP multicast routing, refer to these documents:
