Cabletron Systems SPECTRUM, User Manual

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Using the 7C0x SmartSwitch Bridge View
6-22 The Spanning Tree Protocol Window
Designated Root
This value represents the bridge that is the current Root Bridge as determined by
the STA. The Designated Root value consists of the configurable portion of the
bridge ID (i.e., the first two octets of the eight-octet-long bridge ID) and the root
bridge device’s MAC address (the last six octets of the bridge ID). This value is
used as the Root Identifier parameter in all configuration BPDUs originated from
this node.
Num. Topology Chgs.
Indicates the number of times the bridge’s Topology Change flag has been
changed since the bridge was powered up or initialized. The Topology Change
flag increments each time any of the network’s bridges enters or leaves the
network or when the Root Bridge ID changes.
The values for the following three fields—Forward Delay, Max Age, and Hello
Time—represent the values that are currently being used by all bridges, as
dictated by the Root bridge. In the Spanning Tree Protocol window, you can view
and set the values—Root Forward Delay, Root Max Age, Root Hello Time—that
will be in effect when the bridge for which you are setting the parameters
becomes the Root Bridge.
Forward Delay
The length of time, in seconds, that controls how long a bridge port remains in
each state (Forwarding, Learning, Listening, etc.) when moving toward the
Forwarding state. During a topology change, the Forward Delay is also used as
the Filtering Database Ageing Time, which ensures that the Filtering Database
will contain current topology information. The Root Bridge sets the Forward
Delay.
Max Age
The current setting for the bridge’s BPDU ageing timer, in seconds. The ageing
timer defines the maximum number of seconds that a Configuration BPDU is
retained by the bridge before it is discarded. During normal operation, each
bridge in the network receives a new Configuration BPDU before the ageing timer
expires. If the timer expires before a new 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indicates that the former Root is no longer active.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 Root Bridge determines the
Max Age. The range for this field is from 6 to 40 seconds, with a default value of
20 seconds.
!
CAUTION
All bridges in a network must use the same Spanning Tree version. Mixing Spanning Tree
Algorithm protocols will cause an unstable network.