3Com 2500 manual 1 shows a simple network with five links

5-4 CHAPTER 5: ROUTING WITH IP MULTICAST

Figure 5-1 shows a simple network with five links.

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3

D

1

B

4

6 E

2

C

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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.

A

3

D

1

B

4

6 E

2

C

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Figure 5-2 Spanning Tree Algorithm Implemented to Block Redundant Paths

Reverse Path Reverse path forwarding (RPF) is the multicast algorithm in use on the Forwarding 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:

1When 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.

2If 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.

3If the condition in Step 2 is false, the system drops the packet.