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network convergence might take a long time. H3C recommends that you use the automatically
calculated value.
•
An appropriate hello time setting enables the device to promptly detect link failures on the network
without using excessive network resources. If the hello time is too long, the device mistakes packet
loss for a link failure and triggers a new spanning tree calculation process. If the hello time is too
short, the device frequently sends the same configuration BPDUs, which waste device and network
resources. H3C recommends that you use the automatically calculated value.
•
If the max age timer is too short, the device frequently begins spanning tree calculations and might
mistake network congestion as a link failure. If the max age timer is too long, the device might fail
to promptly detect link failures and quickly launch spanning tree calculations, reducing the
auto-sensing capability of the network. H3C recommends that you use the automatically calculated
value.
Configuration procedure
To set the spanning tree timers:
Step Command Remarks
1.
Enter system view.
system-view
N/A
2.
Set the forward delay
timer.
•
In STP/RSTP/MSTP mode:
stp timer forward-delay
time
•
In PVST mode:
stp vlan
vlan-id-list
timer
forward-delay
time
The default setting is 15 seconds.
3.
Set the hello timer.
•
In STP/RSTP/MSTP mode:
stp timer hello
time
•
In PVST mode:
stp vlan
vlan-id-list
timer hello
time
The default setting is 2 seconds.
4.
Set the max age timer.
•
In STP/RSTP/MSTP mode:
stp
timer max-age
time
•
In PVST mode:
stp vlan
vlan-id-list
timer max-age
time
The default setting is 20 seconds.
Setting the timeout factor
The timeout factor is a parameter used to decide the timeout period, in the following formula: Timeout
period = timeout factor × 3 × hello time.
In a stable network, each non-root-bridge device forwards configuration BPDUs to the downstream
devices at the hello time interval to detect link failures. If a device does not receive a BPDU from the
upstream device within nine times the hello time, it assumes that the upstream device has failed. Then, it
starts a new spanning tree calculation process.
A device might fail to receive a BPDU from the upstream device because the upstream device is busy. If
a spanning tree calculation occurs, the calculation can fail and also waste network resources. On a
stable network, you can prevent undesired spanning tree calculations by setting the timeout factor to 5,
6, or 7.