Spanning Tree Root Path Cost

[Sagar4]

Tell me root path cost for paths 1 and 2. Please explain calculation. I have attached same image pasted above.

[balaji.bandi]

This all depends on the config (and if no config applied) - based on the negotiations (since some ports gig connected to fas ethernet

here is the logic applied for STP cost based on the Link speed :

Link Speed	Cost (Revised IEEE 802.1D-1998 Specification)
10 Gbps	2
1 Gbps	4
100 Mbps	19
10 Mbps	100

[Martin L]

Cost to Root switch is based on Link cost (based on speeds manually configured or auto-negotiated) and cumulative patch cost to Root. Root switch sends BPDU with cost of 0; Each Neighboring switches will add its own cost and advertise that out to their neighbors. Sw B cost to Root is 4, sw C cost is 8 (4+4), and so on.  Sw G cost to A is 19 -see note below

In ring topology, each switch has 2 path costs to Root and has to make a choice based on lower cost. In your topology settings, Sw F seems to be at the crossroads.  Sw F could reach Root via E with cost 20 (5x4) OR via G with cost 21 (19 +4).  Sw F chooses lower path cost via E, D, C, B.  

Note: The only issue in your picture is sw G with link cost of 19, not 4, since link speed is 100Mbps not 1G. Speed is negotiated down to lower operational speed possible between Fast-Ethernet and Gig Ethernet.

Regards, ML
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[MHM Cisco World]

Sincr all link is G (I assume it 1 G)

Then the cost is 

4 X number of link to SW you want to calculate cost of it

That it.