PIM Terms and Definitions lists terms and definitions used in PIM configuration.
PIM Terms and Definitions
| Term | Definition |
|---|---|
| Bootstrap Router (BSR) | A PIM router responsible for collecting, within a PIM domain, the set of potential rendezvous points (RPs) and distributing the RP set information to all PIM routers within the domain. The BSR is dynamically elected from the set of candidate BSRs. RP set information includes group-to-RP mappings. |
| Candidate Bootstrap Router (Candidate-BSR) | A small number of routers within a PIM domain are configured as candidate BSRs, and each C-BSR is given a BSR priority. All C-BSRs multicast bootstrap messages (BSMs) containing their priority to the ALL-PIM-ROUTERS group. When a C-BSR receives a bootstrap message from a C-BSR with a higher priority, it stops sending. This continues until only one C-BSR remains sending bootstrap messages, and it becomes the elected BSR for the domain. |
| 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. |
| dense mode | PIM dense mode (DM) uses a source-based tree to distribute multicast data. DM does not require routers on the network to explicitly request interest in a given data stream and assumes that most routers in any given network will be interested in order to maintain efficient operation. |
| 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. |
| Anycast-RP | Anycast-RP provides a means of fast convergence when a PIM RP router fails. All members of the anycast-RP set share the same IP address configured on a loopback interface of each set member. A peer-address associated with the member specifies a unique IP address that identifies the router and can be either a loopback or physical interface. |
| 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. |
| sparse mode | PIM sparse mode (SM) uses a host-initiated process to build and maintain the multicast distribution tree, using only those routers that need to be included in forwarding multicast data. Sparse mode routers use bandwidth more efficiently than other modes, but can require more processing time when working with large numbers of streams |
| source-specific multicast | PIM source-specific multicast (SSM) is a modular switch only subset of the PIM-SM protocol that builds trees rooted in just one source and is used by applications such as content broadcasting. |
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