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

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

STP port priority vs. cost

All,

Am I correct in assuming that cost and port priority do the same thing? Cost seems to be local to the switch and port priority is set by the upstream switch. Is that the case?

Thanks,

John

HTH, John *** Please rate all useful posts ***
1 ACCEPTED SOLUTION

Accepted Solutions

Re: STP port priority vs. cost

Both parameters are used to determine which interface will be in forwarding state.

They have differences though:

If you want to affect how to the local switch elects the root port change the cost on the links. Cost is cumulative throughout the STP domain. The higher cost is the less preferred.

If you want to affect how downstream switch elects its root port change the priority. This is only local significant between the two directly connected switches. Highest priority is less preferred.

Going away from the root of the tree use priority whereas, when going towards the root of the tree use cost.

2 REPLIES

Re: STP port priority vs. cost

Both parameters are used to determine which interface will be in forwarding state.

They have differences though:

If you want to affect how to the local switch elects the root port change the cost on the links. Cost is cumulative throughout the STP domain. The higher cost is the less preferred.

If you want to affect how downstream switch elects its root port change the priority. This is only local significant between the two directly connected switches. Highest priority is less preferred.

Going away from the root of the tree use priority whereas, when going towards the root of the tree use cost.

Re: STP port priority vs. cost

Great explanation! Thanks!

HTH, John *** Please rate all useful posts ***
29429
Views
10
Helpful
2
Replies