Cabletron Systems 9A128-01 Manuale Utente

Bridging

5-14

Bridge Spanning Tree

2.

Type in the new Ageing Time (allowable range is 10 to 1,000,000 seconds; the 
default is 300 seconds).

3.

Click 

 to accept the new Ageing Time, or click 

 to exit the 

window without making changes.

The Bridge Spanning Tree window allows you to display and modify the selected 
module’s 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 configured to filter (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:

1.

From the Bridge Status window, click on 

 to display the Bridge menu.

From the Module View window, click on the Bridge label in the module 
display; the bridge menu will appear.

2.

Drag down to Spanning Tree..., and release. The Bridge Spanning Tree 
window, 

, will appear.