CANOGA PERKINS 9175 Configuration Guide - Manual (Page 146)

CanogaOS Configuration Guide
24-4
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.
Tree Information Base (TIB)
The TIB is the collection of state at a PIM router storing the state of all multicast
distribution trees at that router. It is created by receiving Join/Prune messages, Assert
messages, and IGMP information from local hosts.
Upstream
Towards to root of the tree. The root of the tree might be either the Source or the RP.