Cisco CLI STP VLAN removal

ciscoclispanning treevlan

Consider the following in the running config in Cisco IOS (switch):

spanning-tree vlan 2-20 prio 4096

If the command "no spanning-tree vlan 5 prio 4096" is issued, will only VLAN 5 be removed without any recomputation of STP topologies of the other VLANs?

Best Answer

Issuing the command no spanning-tree vlan 5 priority 4096, which is the same as spanning-tree vlan 5 priority 32768, will not affect other VLANs' instances of Per VLAN Spanning Tree Plus (PVST+).

Example:

    Eth0/1
+---+            +---+
|SW1+------------+SW2|
+---+            +---+
            Eth0/0

SW2 is hard coded as the root for VLANs 2-20. STP event debugging is enabled on SW1 to illustrate the effect of the change.

SW2(config)#spanning-tree vlan 2-20 priority 4096
SW2(config)#do show run | i prio
spanning-tree vlan 2-20 priority 4096

SW1#debug spanning-tree events
Spanning Tree event debugging is on

SW2's hard coded priority for VLAN 5 is set to default (same effect as negating the hard coded priority).

SW2(config)#spanning-tree vlan 5 priority 32768
SW2(config)#do show run | i prio
spanning-tree vlan 2-4,6-20 priority 4096

SW1#
*Jul 11 11:13:53.266: STP: VLAN0005 heard root 32773-aabb.cc00.0200 on Et0/1
*Jul 11 11:13:55.017: STP: VLAN0005 we are the spanning tree root
*Jul 11 11:13:55.025: STP: VLAN0005 Topology Change rcvd on Et0/1
Related Topic