Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

STP root bridge ?

Hi,

In order to set a switch as the root bridge for STP I can use one of the following two methods:

spanning-tree vlan 'vlan-id' priority 4096

or

spanning-tree vlan 'vlan-id' root {primary}

Is there any other method to configure a switch (3550) as the root bridge ?

I was thinking along the lines of changing the MAC address if the two priorities are tied.

Cheers,

Phil.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: STP root bridge ?

Hi Phil

You cannot change the mac-addresses used for STP calculation on fixed chassis switches - see attached link for details

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801c9b4e.shtml#span_mac

So as the mac-addresses will always be different on different switches manipulating the priority either up or down on switches is the only way to affect the root bridge election.

HTH

Jon

2 REPLIES
Hall of Fame Super Blue

Re: STP root bridge ?

Hi Phil

You cannot change the mac-addresses used for STP calculation on fixed chassis switches - see attached link for details

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801c9b4e.shtml#span_mac

So as the mac-addresses will always be different on different switches manipulating the priority either up or down on switches is the only way to affect the root bridge election.

HTH

Jon

Community Member

Re: STP root bridge ?

Best way is to set STP priority to 0.

This puts switch unconditionally into STP root for VLAN so no other switch can ever beat it.

If you take a step further to make your LAN more deterministic then force another switch to become a secondary

Example: make Switch-1 to become ROOT Bridge for Vlan 100 and 101

Switch-1#

spanning-tree vlan 100,101 priority 0

Switch-2#

spanning-tree vlan 100,101 priority 4096

This makes you LAN solid.

354
Views
0
Helpful
2
Replies
CreatePlease to create content