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626 CHAPTER 38: MSTP CONFIGURATION COMMANDS
interval of the hello time set on the device, while secondary root bridges use the
hello time set on the root bridge.
The setting of the hello time, forward delay and max age timers must meet the
following formulae.
■ 2 × (forward delay - 1 second) ƒ max age
■ Max age ƒ 2 × (hello time + 1 second)
MSTP can work effectively on the entire network only when the above-mentioned
conditions are met; otherwise, network instability will frequently occur. We
recommend that you specify the network diameter of the switched network in the
stp bridge-diameter bridge-number command and let MSTP automatically
calculate an optimal setting of these three timers.
Related commands: stp timer forward-delay, stp timer max-age, and stp bridge-diameter.
Examples # Set the hello time of the device to 400 centiseconds.
<Sysname> system-view
[Sysname] stp timer hello 400
stp timer max-age
Syntax stp timer max-age centi-seconds
undo stp timer max-age
View System view
Parameters centi-seconds: Max age, in the range 600 to 4,000 (in centiseconds). This
argument must be a multiple of 100.
Description Use the
stp timer max-age command to set the max age timer of the device.
Use the undo stp timer max-age command to restore the max age timer of the
device to the default setting.
By default, the max age is set to 2,000 centiseconds.
MSTP can detect link faults and automatically restore the forwarding state of the
redundant link. In the CIST, the device determines whether a configuration BPDU
received on a port has expired based on the max age timer. If a port receives a
configuration BPDU that has expired, that MST instance needs to re-computed.
The max age timer is not meaningful for MSTIs. If the current device is the root
bridge of the CIST, it determines whether a configuration BPDUs has expired based
on the configured max age timer; if the current device is not the root bridge of the
CIST, it uses the max age timer set on the CIST root bridge.