H3C Technologies H3C S12500-X Series Switches - Manual (Page 92)

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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 using the default setting.
• 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 using the default setting.
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. stp timer forward-delay
time
The default setting is 15 seconds.
3. Configure the hello timer. stp timer hello time The default setting is 2 seconds.
4. Configure the max age
timer.
stp 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 time, in the following formula: Timeout time
= timeout factor × 3 × hello time.
After the network topology is stabilized, each non-root-bridge device forwards configuration BPDUs to
the downstream devices at the hello 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
and starts a new spanning tree calculation process.
Sometimes 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
2. Configure the timeout factor
of the device.
stp timer-factor factor The default setting is 3.