MSTP Path cost on LACP trunks?

[Magnus Tengmo]

Hi!

I got 2 5406, 3 2810, connected with 2x1gb LACP trunks, and both 5406 connected with 4x1gb LACP trunks.

If I look at the path cost on the mstp instance at the 5406s, both trunks shows cost 20000.

Shouldn´t I get different costs on trunks links?

Best Regards, Magnus

[Matt Hobbs · Accepted solution]

From memory, when you enable a trunk it will give it a higher spanning-tree priority, but the cost will remain the same. This is also effective at ensuring the trunk will be the forwarding port compared to a regular port.

If you check your running config you should notice something like:

spanning-tree trk1 priority 4