spanning-tree vlan 4 root command

sarahr202 · ‎07-05-2008

hi every body !

I need some help with following :

there are 4 switches sw1,sw2,sw3,sw4

sw1 is configured with:

sw1(config) spanning-tree vlan 4 root primary.

sw 1 configures itself as root after manpalutaing its priorty.

now sw1 is root bridge for vlan 4.

let say we introduce another switch with priorty lower than that of sw1.

(1) will sw1 again modifies its priorty as before and sets its priorty lower than that of sw5 to become root again?

(2)will sw1 not do anything and sw5 becomes a new root bridge?

thanks alot!

Jon Marshall · ‎07-05-2008

Sarah

No sw1 will not modify itself again and the the new switch will become the root bridge - note that this will be done on a per-vlan basis if using PVST+. So sw5 would become the root bridge for vlan 4 but not necessarily for all vlans although if you had used the "spanning-tree vlan x root primary" command for all vlans and the new switch had the lower priority then it would become root for all vlans.

If you want to avoid this you must ensure that the new switch does not have a lower priority or you can lool to enable root-guard within your switched network.

Jon

sarahr202 · ‎07-06-2008

thanks again jon !