How is the cost determined in the Spanning-Tree Protocol determined? Is cost the same as administrative distance?

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The STP cost is an accumulated total path cost based on the bandwidth of the links.

Here's a crappy chart:


Speed___New Cost_Old Cost
10Gbps___1_______ 1
1Gpbs____4_______ 1
100Mbps__19______ 10
10Mbps___100_____ 100

The 1900 swithces (I think) still use the old one. I think the new super-duper ones use the newer ones.

Hope that helped.

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Thanks Trouble Man.
I'm taking my exam next Thurs. Any advise?

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Know that lower is always better in Spanning Tree, for the test. STP use a four step decision to determine a loop free network.
1st. it looks for the bridge with the lowest bridge ID and makes it the root
2nd. It looks for non root bridges that have the lowest path cost to the root bridge and makes these root ports.
3rd. it looks for the port with the lowest Bridge ID to make it a desigated port for the segment
and 4th. in the event of a tie in any of the above decisions it looks for the port with the lowest port ID as the tie breaker.

Also remember the difference between path cost and root path cost.
path cost- is a value assigned to each port. It is added to BPDU's received on that port to calculate the root path cost.
root path cost- is defined as the cummulative cost to the root bridge.

Also know that the default STP priority in a Bridge ID is 32,768
Good luck.

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