Cabletron Systems 9H42X-XX

Bridging

5-14 Bridge Spanning Tree

Protocol

Displays the Spanning Tree Algorithm Protocol type the 9H42x-xx module is

currently using. The choices are:

• 802.1

• DEC (DEC Lanbridge 100)

• None

The following four ﬁelds display values used for various Spanning Tree timers in

the course of normal operations. Three of these values — Hello Time, Max Age,

and Forwarding Delay — are conﬁgurable; the values currently in use are those

which have been set at the Root Bridge. Both the values currently in use and those

which would be used if the monitored 9H42x-xx module were to become the root

bridge are displayed in the upper-right corner of the window. Note that Hold

Time is not conﬁgurable; this is a ﬁxed value and cannot be changed.

Hello Time

This parameter indicates, in seconds, the length of time the Root Bridge (or bridge

attempting to become the Root) waits before resending Conﬁguration BPDUs.

The range for this ﬁeld is 1 to 10 seconds, with a default value of 2 seconds. The

Root Bridge sets the Hello Time.

Max Age

This parameter displays the bridge’s BPDU ageing timer. This controls the

maximum time a BPDU can be retained by the bridge before it is discarded.

During normal operation, each bridge in the network receives a new

Conﬁguration BPDU before the timer expires. If the timer expires before a

Conﬁguration BPDU is received, it indicates that the former Root is no longer

active. The remaining bridges begin Spanning Tree operation to select a new Root.

The current Root Bridge on the network sets the Max Age time. The range for this

ﬁeld is 6 to 40 seconds, with a default value of 20 seconds.

Forwarding Delay

This parameter displays the time period which elapses between states while the

bridge is moving to the Forwarding state. For example, while moving from a

Blocking to a Forwarding state, the port ﬁrst moves from Blocking to Listening to

BPDU activity on the network, remains there for the Forward Delay period, then

moves to the Learning State (and remains in it for the Forward Delay period), and

ﬁnally moves into a Forwarding state. This timer is set by the Root Bridge. During

a topology change, the Forward Delay is also used as the Filtering Database

Aging Time (refer to Filtering Database, page 5-19), which ensures that the

Filtering Database maintains current topology information.

Hold Time

This parameter displays, in seconds, the minimum time that can elapse between

the transmission of Conﬁguration BPDUs through a bridge port. The Hold Time

ensures that Conﬁguration BPDUs are not transmitted too frequently through any

bridge port. Receiving a BPDU starts the Hold Timer. After the Hold Timer