Black Box 5000 series Reference Manual page 172

Higher Value
Setting the value higher will increase the time spent in each of the Listening and Learning States when a
reconfiguration is under way. A higher value will increase the time the network is unavailable for use during
reconfiguration.
Recommendations:
The default value of 15 seconds is recommended by the IEEE 802.1D standard as a reasonable balance of
performance. If a change is deemed necessary, increasing the value in consideration with Message (Max) Age
is the recommended course of action.
The following relationship to Message (Max) Age must be maintained:
2 x (fwd_delay - 1.0) > max_age
4 - Message Age Timer
The Message Age Timer option specifies the length of time stored protocol information is considered valid. If a non-
root bridge hasn't received protocol confirmation from the Root within this interval, it will broadcast to the other
bridges that the topology has changed, and a reconfiguration calculation will be performed.
Default: [20 sec] (IEEE 802.1D recommendation)
Range: 6 to 40 seconds
Considerations:
The Maximum Age of the bridged network is set by the Root Bridge. If a reconfiguration of the bridged
network occurs and this bridge becomes the Root, the value set at this bridge becomes the Network's value.
Lower Value
A much lowered Maximum Age value may cause more frequent reconfigurations of the bridged network
(even if not necessary) if configuration information is delayed. A slightly lower value may trigger a
reconfiguration more quickly should a bridge fail or a management action requests a change.
Higher Value
A higher Maximum Age value will allow more time for confirmation of the network configuration. This
could be beneficial if delays are introduced and the network is frequently "going down" for unnecessary
reconfigurations.
Recommendations:
The default value of 20 seconds is recommended by the IEEE 802.1D standard as a reasonable balance of
performance. If a change is deemed necessary, increasing the value in consideration with Forwarding Delay
and Hello Time is the recommended course of action.
The following relationship to Forwarding Delay must be maintained:
2 x (fwd_delay - 1.0) > max_age
The following relationship to Hello Time must be maintained:
Max Age > 2x (Hello Time + 1.0)
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