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Bridge Spanning Tree 4-35
Bridging
Hop Cnt. Exceeded
Displays the number of All Paths Explorer frames discarded at the speciÞed port
because they exceeded the number of routing descriptors (bridge hops) speciÞed
by the Hop Count Limit.
Bridge 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 to display the Bridge menu.
2. Drag down to select Spanning Tree…. The Bridge Spanning Tree window,
Figure 4-10, will appear.
from the Chassis View window:
1. Click on the Board Index of the device of interest; the Board menu will
appear.
2. Drag down to select Spanning Tree…. The Bridge Spanning Tree window,
Figure 4-10, will appear.