H3C Technologies H3C S5560 Series Switches - Manual (Page 118)

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short, the device frequently sends the same configuration BPDUs, which wastes 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 configure the spanning tree timers:
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure 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. Configure 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. Configure 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.
Configuring the timeout factor
The timeout factor is a parameter used to decide the timeout period. The formula for calculating the
timeout period is: 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.
To configure the timeout factor:
Step Command Remarks
1. Enter system view. system-view N/A