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STP question

Hello folks,

I have a (simple?) question about the spanning tree protocol (STP).

Consider Bridge 1 is the root bridge and both port 1 and two connect to a hub or a lan segment. As the link costs on the ports are both the same, the port ID is used to break the tie. Hence Port 1 of Bridge 1 becomes the designated port.

P1 ------ ----- P1 Bridge 1 Hub/Lan Bridge 2 P2 ------ ----- P2

However, and this is my question, port 1 and 2 of Bridge 2 both receive the same BPDU from Bridge 1. Which one will become the root port considering they have equal link costs defined for the ports?

Thanks to anybody who could explain this to me or single out any fallacies in my reasoning.

Regards, Diego d'Aulignac

Reply to
Diego
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The tie breaker will be the lowest Port Identifier value. Each bridge port is given a 16-bit identifier, which applies only to the ports of that bridge.

In your example, if Bridge 1 becomes the root bridge, and the two links between Bridge 1 and Bridge 2 are of identical cost, then the active link will be the one that goes to the Bridge 2 port with the lowest Port Identifier.

Bert

Reply to
Albert Manfredi

Actually there are four links. I agree that port 1 of bridge 1 (root) will be the designated port, and hence active. However, which of the two ports connecting bridge 2 to the hub/lan will be the root port, and hence active?

D
Reply to
Diego

If there are four links, there must be a third switch between the two you showed in your diagram. The rule is still that the active switch port is the one with the lowest port identifier.

What does "hub/lan" mean, exactly? A LAN, in this context, is merely a link.

Bert

Reply to
Albert Manfredi

I thought that you could connect more than one port of a bridge to a single lan segment, acting like a hub that transmits information to all other ports connected to it. Is this not right?

Thanks for the answers Bert.

Diego

Reply to
Diego

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