Path cost and priority for spanning tree

Unanswered Question
May 9th, 2012

Hi,

May I know how to manually set the priority (root ID and bridge ID priority) and  for spanning tree? Which one should I use based on the command below?

and how does it affect the path cost of it?

set spantree root 1

spanning vlan1 priority 4096

Thank you for ur prompt reply.

I have this problem too.
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PARVESHPALIWAL Wed, 05/09/2012 - 22:03

Hello,

What I know is that you can change the priority of a spanning tree vlan but it has nothing to do with path cost.

Path cost is the cost of a link, usually calculated on the basis of bandwidth of the link. The more the bandwidth the less the cost.

Please let me concern your further queries.

Regards,

Parvesh

ssweehinlew Thu, 05/10/2012 - 01:29

I have core switches and access switches in my network environment and some of the spannning tree vlan root bridge is defined on access switches. How can I change the root bridge from the access switches to core switches without affecting the production network?

glen.grant Thu, 05/10/2012 - 06:26

Determine where you want the root and add the command "spanning tree vlan X root primary" .  

ssweehinlew Mon, 05/14/2012 - 19:49

If I set the vlan root bridge on core switch, do i need to remove it from the access switch? Will it cause downtime?

Some vlans are not joined together, it causes few vlan root bridge are defined on different switches. How to identify the disjoint vlan and join all the vlan via STP?

Cadet Alain Tue, 05/15/2012 - 03:00

Hi,

If I set the vlan root bridge on core switch, do i need to remove it from the access switch? Will it cause downtime?

Of course it cause downtime as there will be a new election and no you don't need to remove it from access switch as long as the priority is better on the core but if the core goes down then your access will be reelected so if you've got another core or distribution switch configure it as a secondary root.

Regards.

Alain

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