Samsung Ubigate iBG3026 Configuration Manual page 159

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 the root of the tree. The root of the tree might be either the Source or
the RP.
Downstream
Away from the root of the tree. The root of tree might be either the Source or
the RP.
Source-Based Trees
In the Source-Based Trees concept, the forwarding paths are based on the
shortest unicast path to the source. If the unicast routing metric is hop counts,
the branches of the multicast Source-Based Trees are minimum hop. If the
metric is delay, the branches are minimum delay.
For every multicast source, there is a corresponding multicast tree that directly
connects the source to all receivers. All traffic to the members of an associated
group passes along the tree made for their source. Source-Based Trees have
two entries with a list of outgoing interfaces--the source address and the
multicast group.
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