Re: Spanning Tree Priority

Well, first of all the rules say your spanning-tree bridge priority is going to have to be a number that is a multiple of 4096. Somehow, that includes 0...I have labbed this up and it works. Let me clarify. You have a 16-bit field called priority. The priority field is futher divided into two pieces -- you have 4 bits for the actual priority, and 12 bits for VLAN ID. The priority field + VLAN ID gives you the overall bridge priority. That 4-bit piece must be 0 or a multiple of 4096

Secondly, to make sure your root stays intact, you should configure the STP Root Guard feature. You are correct in that the spanning-tree root primary command is a one time only deal...it will lower your priority but if something comes on line later that is lower you are out of luck. My recommendation would be set your root to 0 and enable root guard where needed.

Regards,
Joe Astorino, CCIE #24347

"He not busy being born is busy dying" -- Dylan

----- Original Message -----
From: "naman sharma" <naman.prep_at_gmail.com>
To: "Cisco certification" <ccielab_at_groupstudy.com>
Sent: Saturday, May 22, 2010 4:56:33 PM GMT -05:00 US/Canada Eastern
Subject: Spanning Tree Priority

Hi,

Is it advisable to configure Spanning-tree vlan priority to zero in real
world. Although it will add the Vlan Sys-id to the priority in PVST mode.

What is the best practice as configuring spanning tree root primary will
only make sure that the switch becomes the root at that instant but you are
still prone to issues if some switches is added later on with a lower
priority.

Any suggestion ??

thanks

Blogs and organic groups at http://www.ccie.net
Received on Sun May 23 2010 - 00:10:46 ART