Managing The Spanning Tree - 3Com corebuilder 3500 Implementation Manual

344 C 13: IP M
HAPTER
Managing the
Spanning Tree
Source
Potential
hosts
Broadcasting
R
ULTICAST OUTING
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
Source
Pruning
= Multicast router
= Pruned branch
= Active branch
= Graft
Source
Grafting
= LAN without
multicast hosts
= Leaf with
multicast hosts