IPv4 MULTICAST TECHNICAL GUIDE

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On page 23 the term Designated Router (DR) is mentioned and for a non-resilient campus connection it is associated this port. However in a resilient connection, using HSRP or VRRP for unicast, it is important that PIM selects the correct router as the DR. The one that is required is that which follows the primary [HSRP or VRRP] unicast path. PIM selects the DR on the basis of the highest IP address bit it may be more appropriate to specify the DR explicitly rather than leaving it to the default algorithm. In Cisco terms this can be set by

ip pim dr-priority 255

If the wrong router is selected as the DR then multicast fails.

- John A. Linn