Managing The Spanning Tree - 3Com corebuilder 3500 Implementation Manual

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Managing the

Spanning Tree

Broadcasting

The term spanning tree applies to any loopless graph that spans

intelligent nodes. The DVMRP spanning tree structure provides only one

active path to connect any two multicast routers in the network. This

approach provides a logical, efficient path to reach group members and

prevents multicast storms from decreasing network performance.

The Spanning Tree Algorithm that is specified in the IEEE 802.1D MAC

Bridges base standard is a different implementation of the spanning tree

concept; it is not used with IP multicast.

RPM uses three main techniques to dynamically adjust the shape of an IP

multicast spanning tree: broadcasting, pruning, and grafting. These

techniques balance the goal of an efficient delivery path with the goal of

effective service for all potential group members. Figure 69 shows the

broadcasting, pruning, and grafting processes.

Figure 69 RPM Techniques for Managing the Multicast Spanning Tree

= Multicast router

= Pruned branch

= Active branch

= LAN without

multicast hosts

multicast hosts