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5-4 CHAPTER 5: ROUTING WITH IP MULTICAST
Figure 5-1 shows a simple network with five links.
Figure 5-1 Simple Network Implemented Without Using Spanning Tree
A spanning tree for this network consists of links 1, 2, 3, and 4. See
Figure 5-2.
Figure 5-2 Spanning Tree Algorithm Implemented to Block Redundant Paths
Reverse Path
Forwarding
Reverse path forwarding (RPF) is the multicast algorithm in use on the
MBONE network. RPF is designed to avoid duplicate paths on
multi-access links. It uses a routing table to compute a logical spanning
tree for each network source. The RPF algorithm has these basic steps:
1 When the system receives a multicast packet, the algorithm notes the
source network of the packet and the interface on the LANplex system
that received the packet.
2 If the interface belongs to the shortest path towards the source
network, then the system forwards the packet to all interfaces except
the interface on which the packet was received.
3 If the condition in Step 2 is false, the system drops the packet.
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