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Show spanning-tree

Mikdilly

When you do a show spanning-tree does the default port cost infer how many hops away you are from the root bridge, as in 19 would mean 1 hop away, 38 would mean 2 hops?

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Comments

mikearama

Nope... port cost refers to speed on the link.

100Mb/s = 19
while a 10Mb/s link has a cost of 100,
and a Gb link has a cost of 4.

It's not a question of hops, but speed. The link with the lowest cost (highest speed) is selected as root port. Course, if there's multiple links to the root bridge, then the cost is cumulative... so if the cost was 38, you know that the local link is 100Mb/s, and the link on the other side of the next hop is also 100Mb/s. 19 + 19 = 38.

Mike

Mikdilly

mikearama wrote:

Nope... port cost refers to speed on the link.

100Mb/s = 19
while a 10Mb/s link has a cost of 100,
and a Gb link has a cost of 4.

It's not a question of hops, but speed. The link with the lowest cost (highest speed) is selected as root port. Course, if there's multiple links to the root bridge, then the cost is cumulative... so if the cost was 38, you know that the local link is 100Mb/s, and the link on the other side of the next hop is also 100Mb/s. 19 + 19 = 38.

Mike

Thanks, is there any show command on a switch that would tell you how far away from the root bridge you are?