spanning tree

dkblee · ‎08-22-2007

hi! how do i change the native vlan of a switch? The reason is that when i'm trying on spanning tree by connecting 3 switches(2 links in between each switch) together one of the switch prompted that native vlan mismatch.

Anohter question is that, if the default bridge priority 32768 are used for all the 3 switches. Will the non root bridge's priory becomes 32769? That's what i see when i run the command show spanning-tree, not sure why is that so. Pls advise. Thanks.

Jon Marshall · ‎08-22-2007

Hi

On IOS

switchconfig-if)# switchport trunk native vlan "vlan number"

If all bridge priorities are equal then the mac-address will be used to decide the root bridge. Unless you explicitly change the priority then it will not dynamically change to 32769 if it is not the root bridge.

I suspect you are looking at vlan 1 when you see a priority of 32769. This the extended system-id and you add the vlan number to the default spanning-tree priority. So vlan 10 would have a priority of 32778.

Hope this helps

Jon

lamav · ‎08-22-2007

When you say you have "2 links between each switch," I am assuming that you are creating an etherchannel and binding the 2 physical links into one logical channel.

If that is so, all ports that will be part of the etherchannel must have the same:

1. Speed and duplex settings.

2. Native vlan setting.

3. Must all be in the same vlan if the ports are access ports. If its a trunk, all must be configured to carry the same vlans.

3. The native vlan must be the same on all ports, too.

Follow Jon's instruction to change the native vlan setting.