Cabletron Systems 2.2 Manual De Usuario

Bridging

2-34

Spanning Tree

The Bridge Spanning Tree window allows you to display and modify the deviceÕs 
bridge port information and protocol parameters relating to the Spanning Tree 
Algorithm.

In a network design with multiple bridges placed in parallel (i.e, attached to the 
same LAN), data loops must be prevented. The Spanning Tree Algorithm (STA) is 
the method that bridges use to communicate with each other to ensure that only a 
single data route exists between any two end stations. 

On a LAN interconnected by multiple bridges, Spanning Tree selects a controlling 
Root Bridge and Port for the entire bridged LAN, and a Designated Bridge and 
Port for each individual LAN segment. A Designated Port/Bridge for a LAN 
segment forwards frames from that LAN towards the Root Bridge, or from the 
Root Bridge onto the LAN. All other bridge ports attached to that LAN are 
conÞgured to Þlter (block) frames. 

When data passes from one end station to another across a bridged LAN, it is 
forwarded through the Designated Bridge/Port for each LAN segment towards 
the Root Bridge, which in turn forwards frames towards Designated 
Bridges/Ports on its opposite side.

During the Root Bridge Selection process, all bridges on the network 
communicate STA information via Bridge Protocol Data Units (BPDUs). With 
BPDUs, all network bridges collectively determine the current network topology 
and communicate with each other to ensure that the topology information is kept 
current.

To access the Bridge Spanning Tree window from the Bridge Status window:

1.

Click on Bridge to display the Bridge menu.

2.

Click on Spanning Tree. The Bridge Spanning Tree window, 

appear.

To access the Bridge Spanning Tree window from the 

Chassis View

 window: 

1.

Click on the Board Index of the device of interest; the Board menu will 
appear.

2.

Click on Spanning Tree. The Bridge Spanning Tree window, 

appear.