The snapshot is a tutorial of Switch.

You see the bellow snapshot, from the ROOT SW1 node to SW3, there are two path:

the author says the the path1(left side path) cost is 0 + SW3-in-port. the path2(right side path) cost is 0 + SW2-in-port + SW3-in-port.

there I have a doubt, why author do not use the passing Switches node as the cost value? if the data passing port can represent cost, why the Switch out port do not have value?

1 Answer 1


For SW3, the left root path has a cost of 2,000,000, and the right path has a cost of 2,000,000 + 200,000 = 2,200,000. It chooses the lower cost = left path.

If the link between SW2 and SW3 was 100BASE-TX as well, the cost would decrease to 400,000 and SW3 would choose the right-hand path.

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