Multicast and Routing Guide K/KA/KB.15.15

NOTE: While the use of C-RPs and a BSR enable a dynamic selection of RPs for the multicast
group traffic in a network, using static RPs involves manually configuring all routers in the domain
to be aware of each static RP. This can increase the possibility of multicast traffic failure from to
misconfigurations within the PIM-SM domain. Also, because a BSR does not administer static RPs,
troubleshooting PIM-SM traffic problems can become more complex. For these reasons, use of
static RPs should be limited to applications where no viable alternatives exist, or where the network
is stable and requires configuring and maintaining only a few routers.
If a static RP operating as the primary RP for a multicast group fails, and the PIM-SM configuration
in the domain does not include a (secondary) dynamic RP (C-RP) backup to the static RP, then new
multicast groups assigned to the static RP will not be available to multicast receivers in the domain.
Also, if a static RP fails, support for existing groups routed through SPTs that exclude the failed
router will continue, but any existing flows routed through the RPT will fail.
Supporting a static RP as primary
A static RP can be configured to operate as either a secondary or primary RP. With the primary
option, a dynamic (C-RP) backup is recommended. The precedence of a static RP over a dynamic
RP is determined by the following static RP configuration options:
• override enabled on the static RP.
• A group mask on the static RP that equals or exceeds the group mask on the C-RP for the same
multicast group(s.)
For override configuration information, see “Statically configuring an RP to accept multicast
traffic” (page 77).
Operating rules for static RPs
• Static RPs can be configured on the same routers as C-RPs.
• Where a C-RP and a static RP are configured to support the same multicast group(s), the C-RP
takes precedence over the static RP unless the static RP is configured to override the C-RP. (See
“Supporting a static RP as primary” (page 100).)
• Any static RP in a domain must be configured identically on all routers in the domain.
Otherwise, some DRs will not know of the static RP and will not forward the appropriate
multicast traffic, and some routers will not know where to send Joins for the groups supported
by static RP.
• Up to four static RP entries can be configured on a router. Each entry can be for either a single
multicast group or a range of contiguous groups.
• Only one interface can be configured as the static RP for a given multicast group or range of
groups. For example, a properly configured PIM-SM domain does not support configuring
10.10.10.1 and 10.20.10.1 to both support a multicast group identified as 239.255.255.10.
• Static RPs are not included in the RP-set messages generated by the BSR, and do not generate
advertisements.
• If a static RP becomes unavailable, it is necessary to remove and/or replace the configuration
for this RP in all routers in the domain.
Configuration
See “Statically configuring an RP to accept multicast traffic” (page 77).
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.
100 PIM-SM (Sparse Mode)