STP vlan bridge root cost question..

I have a question about the vlan and bridge root cost. my topology on vlan 40, the sw2-1 it's the bridge root cost and sw 2-3 and sw 2-2 are cost is 4. the question it's from 2-4 to get to root bridge I need to pass from 2-2 or 2-3 to get to 2-1, the cost is 4, why is not 8?

sorry I hope this can explain.

thank you so much.

root brige.jpg

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Comments

clarson

don't have a clue. Maybe if you show us the topology we might be able to help you

CertifiedMonkey

Maybe they're referring to the port cost and not the total cost to root?

Remember: Default Port Costs are
10 Mbps = 100
100 Mbps = 19
1 Gbps = 4
10 Gbps = 2

What is the output of show spanning-tree vlan 40? It should be similar to the following:

Switch2-4#show spanning-tree vlan 40
VLAN0040
Spanning tree enabled protocol ieee
Root ID Priority 32808
Address xxxx.xxxx.xxxx
Cost 8 <

Total Cost to root

! output omitted

Interface Role Sts Cost Prio.Nbr Type

---- ---

G0/2 Root FWD 4 <

Port cost 128.26 P2p