3Com TR manual Spanning Tree Fields, Spanning Tree Parameters

5In the Spanning Tree field, select *802.1d* to enable 802.1d compliant Spanning Tree for the Switch 2000 TR. The BPDU value is automatically assigned:

80-01-43-00-00-00.

6Select OK. Repeat for all ports as desired.

Spanning Tree Fields

Spanning Tree is an algorithm designed to eliminate loops in networks. The algorithm detects and logically prohibits redundant paths by placing some bridge ports in the blocking state so that only one route exits between any two LANs and therefore any two sta- tions. After Spanning Tree eliminates redundant paths, the network reconfigures and stabilizes. Any time the network topology changes the algorithm automatically re-learns the new configuration and adjusts the bridge ports accordingly. This guarantees that all stations are connected.

Spanning Tree Parameters

The following parameters are components of the Spanning Tree algorithm. These are set to factory defaults.

■Priority—This setting influences the choice between the root bridge and the designated bridge. The bridge with the lowest priority is the one most likely to be used as the root bridge by Spanning Tree.

■Entry Age—The period of time that must expire between sends before a MAC address is “aged out” (removed) from the switch data base (transparent bridging table).

Bridge Configuration 4-5

■Bridge Hello Time—The period of time between the generation of configuration messages by a root bridge is known as Hello Time.

In networks where the probability of losing config- uration messages is high, a short Hello Time is desirable. In networks that are fairly stable, a longer time lowers the overhead of the Spanning Tree algorithm.

■Bridge Max. Age—Maximum Age determines the amount of time the current Spanning Tree con- figuration data is judged too old and discarded from the Switch 2000 TR’s memory. Maximum Age should never be reached in a properly configured Spanning Tree.

If this value is too small, the Spanning Tree must configure too frequently. If this setting is too high the network requires more time to adjust to changes in the topology.

■Forward Delay—The Forward Delay value deter- mines the amount of time the Switch 2000 TR spends in the “listening “and “learning” states. This prevents the forwarding of data packets until all parts of the topology have been notified of a change in the topology.

A low value can result in temporary loops as the Spanning Tree reconfigures the topology. A setting that is too high forces the network to wait longer for Spanning Tree to reconfigure the topology.

NOTE:For more information on Spanning Tree and bridging concepts refer to Interconnections:Bridges and Routers by Radia Perlman. Addison-Wesley Pub- lishing Company, Reading MA. © 1992.