The Spanning Tree Algorithm - 3Com LANPLEX 2500 Operation Manual

The Spanning Tree
Algorithm
Transmitting station
1
Bridge A
1b
1c
Figure 5-3 Packets Looping and Multiplying Without Spanning Tree Protocol
The Spanning Tree algorithm detects loops and logically blocks (eliminates)
redundant paths by putting some bridge ports in the blocking state so that
only one path exists between any two LANs and, therefore, between any
two stations. See Figure 5-4. A port in the blocking state neither forwards
nor receives data packets.
After the algorithm eliminates extra paths, the network configuration
stabilizes. When one or more of the bridges or communication paths in the
stable topology fail, the protocol automatically recognizes the changed
configuration and activates redundant links. This activation ensures that all
stations remain connected.
Spanning Tree and the Bridged Network
1
Bridge B
1c
1a
5-7
LAN 1
1
Bridge C
1a 1b
LAN 2