Easy Spanning tree question

[adelbano33]

Hello gurus.

I have a spanning-tree doubt that sure you can answer me easily.

Imagine you have a network with some loops so spanning tree is blocking redundant ports.

If you have bad placed the root switch (imagine that you have it in the last switch in a cascade) and link to root is flapping.

1st question: Every time you lost connection to root, network recalcule again the root  process?

2nd question:Do you will enter into a loop until root is present again?

Thanks a lot for your answer!

Albert.

[Joseph W. Doherty]

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Posting

#1 If the rest of the topology loses access to the root bridge, yes a new root should be selected.

#2 No, assuming there was no loop before the connection was lost to the root, there shouldn't be any loop when the root is "lost".  However, once the topology starts to decide on the new root, and a new logical loop free topology is implemented from the new root, I believe the whole topology will block for some (hopefully short) duration.

[adelbano33]

Thanks for your help.

Yes, imagine there are several loops, but they are blocked for spanning-tree.

The question is if while root switch is elected, because as you say always spanning tries to found a root, all switches ports are forwarding again and loop accours again...

Thanks

[Joseph W. Doherty · Accepted solution]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

No, as I believe a new root election will be like a new spanning tree startup, i.e. all devices will block all their ports as they learn and decide what the loop free topology is and implement it.  So instead of there being temporary loops, you'll have a temporary outage, as I've noted in my first posting.  (NB: I'm also assuming multiple path links don't have portfast enabled.)

Losing a root bridge is a "big deal", which is another reason why which device is used for it merits careful consideration.