Help with practice test question

I'm having trouble understand the answers to this question

I understand that there's 1 designated port per segment, but why is port Fa0/0 on switch B the designated port, and not Fa0/0 on switch A? Both ports are on the same segment, and they are equal distance from the root bridge.

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Comments

networker050184

Wheres the question???

ignign0kt

in the image...

networker050184

I can't see the image, but I think what you are asking is which port is used as the designated port if the root path is equal on both switches. If the root path is equal the bridge id will be used next and the lower bridge id will win.

Netstudent

They are counting the ports on the root bridge(B) as designated ports. Then as networker said, it's the lowest bridge ID if the costs are the same.

port fa0/0 on switchC is switchC's root port and the fa0/0 port on switchA is a root port.

Then between switch A and C, A is advertising the lower Bridge ID, therefore it is the designated bridge on the segment and port fa0/1 is also designated.

networker050184

All ports on the root bridge become dp on all segements because they advertise the lowest root path cost (0).

ignign0kt

So the port with the lowest mac address on the segment gets chosen as the designated port if the cost if the same? Otherwise the closest is chosen?
Sounds about right to me. Thanks guys

networker050184

Not the port with the lowest MAC, the bridge ID is used. The bridge ID consits of the priority and the MAC address of the switch. It is not the "closest" that is chosen either. It is the lowest cost. A switch can be farther and have a lower cost do to higher speed links.