H3C S6850 Series Configuration Manual page 302

As a best practice, specify the network diameter and letting spanning tree protocols automatically
calculate the timers based on the network diameter instead of manually setting the spanning tree
timers. If the network diameter uses the default value, the timers also use their default values.
Set the timers only on the root bridge. The timer settings on the root bridge apply to all devices on the
entire switched network.
Restrictions and guidelines
•
The length of the forward delay is related to the network diameter of the switched network. The
larger the network diameter is, the longer the forward delay time should be. As a best practice,
use the automatically calculated value because inappropriate forward delay setting might cause
temporary redundant paths or increase the network convergence time.
•
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
wastes device and network resources. As a best practice, 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. As a best practice, use the automatically calculated
value.
Procedure
Enter system view.
1.
system-view
Set the forward delay timer.
2.
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.
Set the hello timer.
3.
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.
Set the max age timer.
4.
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.
33