Spanning tree

acbenny · ‎08-22-2007

Hi all,

If three switch connected as seris like a circle, then STP will elect the root bridge within three switch.

How about if two switch connected with a single link, Will STP occur and will Root bridge will be elected ?

jwdoherty · ‎08-22-2007

No, not with two switches and just one link.

STP breaks topology loops. With only two switches you need two or more links connected between the pair.

Richard Burts · ‎08-22-2007

Jack

If two switches are connected with a single link then Spanning Tree will run, BPDUs will be sent over the link, and a Root Bridge will be elected. In this case no ports will go into blocking mode (if the switches are connected with a single link there is no possibility of a loop so no blocking).

[edit] with all due respect to Joseph, whose response got in just barely before mine, even with 2 switches STP will run. Your answer emphasizes that there can be no loop and therefore no blocking. But that does not mean that STP does not run.

HTH

Rick

HTH

Rick

jwdoherty · ‎08-22-2007

Richard is 100% correct, spanning tree, if enabled, will run. (And often a good idea to enable to avoid "accidents" when someone mis-patches or someone brings in a "personal" switch even for topologies that don't have intended multiple paths for redundancy.)

You're also correct, what I had in mind was STP wouldn't have any loop to break in a 2 switch one link connection unlike the 3 switch loop described as part of the original question.

Again, Richard, thanks for the correction.

Edison Ortiz · ‎08-22-2007

> How about if two switch connected with a single link, Will STP occur and will Root bridge will be elected ?

Yes.