Operating rules and recommendations

Guideline for configuring C-RPs and BSRs

Routers in a PIM-SM domain should usually be configured as both C-RPs and candidate BSRs; this can reduce some overhead traffic.

The SPT policy should be the same for all RPs in a domain.

Allowing some RPs to remain configured to implement SPTs while configuring other RPs in the same domain to force RPT use can result in unstable traffic flows. (Use the no ip pim-sparse spt-threshold command to change between SPT and RPT operation on each router.)

Application of RPs to multicast groups.

In a PIM-SM domain, a given multicast group or range of groups can be supported by only one RP. (Typically, multiple C-RPs in a domain are configured with overlapping coverage of multicast groups, but only one such candidate will be elected to support a given group.)

Ensuring that the C-RPs in a PIM-SM domain cover all desired multicast groups.

All of the multicast groups you want to allow in a given PIM-SM domain must be included in the aggregate of the multicast groups configured in the domain's C-RPs. In most cases, all C-RPs in a domain should be configured to support all RP groups (the default configuration for a router enabled as a C-RP.) This provides redundancy in case an RP becomes unavailable. (If the C-RP supporting a particular multicast group becomes unavailable, another C-RP is elected to support the group as long as there is redundancy in the C-RP configuration for multiple routers.) Note that is cases where routers are statically configured to support a specific group or range of groups, the C-RP prioritization mechanism allows for redundant support.


These two features cannot both be enabled on the same router at the same time.

Supporting PIM-SM across a PIM Domain.

To properly move multicast traffic across a PIM-SM domain, all routers in the domain must be configured to support PIM-SM. That is, a router without PIM-SM capability blocks routed multicast traffic in a PIM-SM domain.