Specifications

Understanding Multicast
April 16, 2009 Page 14 of 32
Rendezvous Point (RP) The root of a group-specific distribution tree whose branches extend to all
nodes in the PIM domain that want to receive traffic sent to the group.
RPs provide a place for receivers and senders to meet. Senders use RPs to
announce their existence, and receivers use RPs to learn about new senders of
a group.
The RP router, for the group, is selected by using the hash algorithm defined in
RFC 2362.
Candidate Rendezvous
Point (Candidate-RP)
PIM routers configured to participate as RPs for some or all groups.
C-RPs send C-RP Advertisement messages to the BSR. The messages contain
the list of group prefixes for which the C-RP is willing to be the RP. Once the
PIM-SM routers receive the BSR’s message, the routers use a common
hashing algorithm to hash the C-RP address, group, and mask together to
identify which router will be the RP for a given group.
A C-RP router must also learn which PIM-SM router is the BSR. Each
designated candidate-BSR (C-BSR) asserts itself as the BSR, then defers once
it receives a preferable BSR message. Eventually, all C-RPs send their
messages to a single BSR, which communicates the Candidate RP-set to all
PIM-SM routers in the domain.
Static RP If a BSR is not used to distribute RP set information, RP-to-group mappings are
configured statically on each router.
Static RP configuration and use of bootstrap routers are mutually exclusive. You
should not configure both in a PIM-SM domain because such configuration
could result in inconsistent RP sets. Statically configured RP set information will
take precedence over RP set information learned from a BSR.
Designated Router (DR) A designated router is elected from all the PIM routers on a shared network.
DRs are responsible for encapsulating multicast data from local sources into
PIM-SM register messages and for unicasting them to the RP. The router with
the highest priority wins the DR election. In the case of a tie, the router with the
highest IP address wins.
PIM Domain A contiguous set of routers that implement PIM and are configured to operate
within a common boundary defined by PIM multicast border routers.
PIM Multicast Border
Router (PMBR)
A router that connects a PIM domain to other multicast routing domains.
Table 1 PIM Terms and Definitions (continued)
Term Definition