CANOGA PERKINS CanogaOS Configuration Guide - Manual (Page 178)

CanogaOS Configuration Guide
Proprietary & Confidential Canoga Perkins Metro Ethernet Switches Page 178 of 350
Note: the Ac in the LastReporter column denotes that this group will be counted when
calculating max group number.
24.3 PIM-SM Configuration
The Protocol Independent Multicasting-Sparse Mode (PIM-SM) is a multicast routing protocol
designed to operate efficiently across Wide Area Networks (WANs) with sparsely distributed
groups. It helps network nodes that are geographically dispersed to conserve bandwidth, and
reduces traffic by simultaneously delivering a single stream of information to multiple locations.
PIM-SM uses the IP multicast model of receiver-initiated membership, supporting both shared
and shortest-path trees, and uses soft-state mechanisms to adapt to changing network conditions.
It relies on a topology-gathering protocol to populate a multicast routing table with routes.
24.3.1 References
The PIM-SM module is based on the following IETF draft:
RFC 4601
24.3.2 Terminology
Following is a brief description of terms and concepts used to describe the PIM-SM protocol:
Rendezvous Point (RP)
A Rendezvous Point (RP) router is configured as the root of the non-source-specific distribution
tree for a multicast group. Join messages from receivers for a group are sent towards the RP.
Data from senders is sent to the RP so that receivers can discover who the senders are, and
receive traffic destined for the group.
Multicast Routing Information Base (MRIB)
The MRIB is a multicast topology table derived from the unicast routing table. In PIM-SM, the
MRIB is used to decide where to send Join/Prune messages. It also provides routing metrics for
destination addresses. These metrics are used when sending and processing Assert messages.
Reverse Path Forwarding
Reverse Path Forwarding (RPF) is a concept of an optimized form of flooding, where the router
accepts a packet from SourceA through Interface IF1 only if IF1 is the interface the router would
use in order to reach SourceA. It determines whether the interface is correct by consulting its
unicast routing tables. The packet that arrives through interface IF1 is forwarded because the
routing table lists this interface as the shortest path to the network. The router's unicast routing
table determines the shortest path for the multicast packets. Because a router accepts a packet
from only one neighbor, it floods the packet only once, meaning that (assuming point-to-point
links) each packet is transmitted over each link once in each direction.