H3C H3C S7500E-X, Configuration Manual

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its state after a forward delay timer to make sure the state transition of the local port stays
synchronized with the peer.
•
Hello time
—Interval at which the device sends configuration BPDUs to detect link failures. If
the device receives no configuration BPDUs within the timeout period, it recalculates the
spanning tree. The formula for calculating the timeout period is timeout period = timeout factor ×
3 × hello time.
•
Max age
—In the CIST of an MSTP network, the device uses the max age timer to determine
whether a configuration BPDU received by a port has expired. If it has, a new spanning tree
calculation process starts. The max age timer does not take effect on other MSTIs except the
CIST.
To ensure a fast topology convergence, make sure the timer settings meet the following formulas:
•
2 × (forward delay – 1 second) ≥ max age
•
Max age ≥ 2 × (hello time + 1 second)
As a best practice, specify the network diameter instead of manually setting the spanning tree timers.
The spanning tree protocols will automatically calculate the timers based on the network diameter. 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.
Configuration restrictions and guidelines
•
The length of the forward delay timer 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.
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:
The default setting is 2 seconds.