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Configuring Interface Priority for PIM Designated Router Selection

A designated router (DR) sends periodic join messages and prune messages toward a group-specific rendezvous point (RP) for each group for which it has active members. When a Protocol Independent Multicast (PIM) router learns about a source, it originates a Multicast Source Discovery Protocol (MSDP) source-address message if it is the DR on the upstream interface.

By default, every PIM interface has an equal probability (priority 1) of being selected as the DR, but you can change the value to increase or decrease the chances of a given DR being elected. A higher value corresponds to a higher priority, that is, greater chance of being elected. Configuring the interface DR priority helps ensure that changing an IP address does not alter your forwarding model.

Note:

DR priority is specific to PIM sparse mode; as per RFC 3973, PIM DR priority cannot be configured explicitly in PIM Dense Mode (PIM-DM) in IGMPv2 – PIM-DM only support DRs with IGMPv1.

To configure the interface designated router priority:

  1. This example shows the configuration for the routing instance. Configure the interface globally or in the routing instance.
  2. Verify the configuration by checking the Hello Option DR Priority field in the output of the show pim neighbors detail command.