The set protocols spanning-tree pvst vlan forward-delay command sets the value of the Rapid-PVST+ forward delay interval of a switching device.
set protocols spanning-tree pvst vlan <vlan-id> forward-delay <forward-delay>
Specifies the VLAN ID. The value is an integer that ranges from 1 to 4094.
Specifies the value of the Forward Delay. The value is an integer, in seconds, that ranges from 4 to 30. The default value 15s.
On a network running a spanning tree algorithm, if the network topology is changed, it takes time to advertise new BPDU configuration messages on the network. During this period, interfaces to be blocked may not be blocked in time and interface ever blocked may not be blocked. As a result, a temporary loop may be formed. To prevent this problem, you can use the Forward Delay timer to set a delay time. During the delay time, all interfaces are blocked temporarily.
The relationships between the Hello Time, Forward Delay, and Max Age are as follows. The spanning tree functions properly only if the correct relationships are established. Otherwise, frequent network flapping occurs.
- Set the value of the Rapid-PVST+ forward delay interval of a switching device to 20s.