Thursday, January 15, 2009

Multicast - BSR

I recently came across a lab scenario where 3 routers were operating in PIM Sparse mode. The question stated that an interface on one router should join a multicast group and all other routers should be able to ping this address.

The sting in the tail was that the configuration must be achieved on only 1 router and the 'ip pim autorp listener' command could NOT be used.

The obvious answer would have been to have configured auto rp. However a pre-requisite for this to work in a PIM sparse mode environment would be for the 'ip pim autorp listener' command to be configured on all routers in the domain.

The way around this problem is to configure BSR (bootstrap routing). This can operate in sparse mode without the 'autorp listener' prerequisite.

Therefore on one of the routers the place the following configuration

ip pim rp-candidate lo0
ip pim bsr-candidate lo0

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