H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 70)

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Configuring spanning tree timers
The following timers are used for spanning tree calculation:
• Forward delay
It is the delay time for port state transition. To prevent temporary loops on a network, the spanning tree
sets an intermediate port state, the learning state, before it transitions from the discarding state to the
forwarding state, and requires that the port transitions its state after a forward delay timer to ensure that
the state transition of the local port keeps synchronized with the peer.
• Hello time
The device detects whether a link failure has occurred with the hello time interval. The spanning tree
sends out a configuration BPDU every hello time interval. If the device receives no configuration BPDUs
within the hello time interval, it recalculates the spanning tree.
• Max age
In the CIST of an MSTP network, the device determines whether a configuration BPDU received by a port
has expires based on the max age timer. If yes, a new spanning tree calculation process starts. The max
age timer is ineffective for MSTIs.
To prevent network instability, make sure that the timer settings meet the following formulas:
• 2 × (forward delay – 1 second) ú max age
• Max age ú 2 × (hello time + 1 second)
H3C does not recommend you to manually set the spanning tree timers. Instead, you can specify the
network diameter and let spanning tree protocols automatically calculate the timers based on the
network diameter. If the network diameter uses the default value, the timers also use their default values.
Configure the timers on the root bridge only, and the timer settings on the root bridge apply to all the
devices on the entire switched network.
Follow these steps to configure the spanning tree timers:
To do... Use the command... Remarks
Enter system view system-view —
Configure the forward delay timer stp timer forward-delay time
Optional
1500 centiseconds by default.
Configure the hello timer stp timer hello time
Optional
200 centiseconds by default.
Configure the max age timer stp timer max-age time
Optional
2000 centiseconds by default.