Spanning tree question: taking FE over GE

[billmatthews]

I have three switches.  Switch1 has Gig links to the other two switches.  Switch2 and 3 have a 100mb link between them.  Drawing attached (red are Gig, blue is 100mb). 

But for some reason switch3 thinks the way to the root is the 100mb link to switch2, then take the gig to switch1. 

From switch3, you'll see the FE is the root port, even though the GE has a lower port cost:

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/1           Root FWD 3019      128.22   P2p

Gi0/2            Altn BLK 3004      128.26   P2p

Any ideas where I should look?

Thanks

[cadet alain]

Hi,

Can you post running-config of 3 switches. These are weird cost values.

Regards.

Alain.

[grinch182 · Accepted solution]

I belive it happenes because your FE port is a root port, so it' doesn't matter if your second link has higher bandwidth. Make SW1 a root-bridge and you will see  the result.

Sincerely,

GRinch

[billmatthews]

Thanks guys. 

GRinch, that was the problem -- wrong root-bridge.  Forcing sw1 fixed the problem!

Bill

[grinch182]

I'm glad you solved the problem.

-GRinch