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
98.
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
on page 123.)
• 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.
Chapter 4 PIM-SM (Sparse Mode)
123
