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spanning tree state & connectivity

suthomas1
Level 6
Level 6

Two offices connected to each other over direct links in close distance.
Office-B1 switch appears to the root for all vlans.

The Office-B1 switch will be cut off from the main office. there will not be any direct link between
both switches. In doing this, will the main office vlans have any issues in terms of spanning tree?

After the link between the main office & Office-B1 is cut off , will the main office switch(without losing connectivity for its clients) realise that it itself will be the root since the link to office-B1 is no longer there.Will there be any outage due to this for main office switch?

(this is closely related to another question i posted in the community, but i forgot to ask this bit
& marked that answered- hence posting another one)
Please help. Thanks

1 Accepted Solution

Accepted Solutions

in that case, you will not have an issue, as there is no spanning tree paths on a single switch.

 

I would however advise you to start naming your VTP domain and make the one switch the server. and possibly add a password to the vt domain, this way its more scalable for future expansion and will prevent someone plugging a switch in and taking over as VTP server by accident and screw up your vlans (believe me i have seen this happen)

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View solution in original post

4 Replies 4

Dennis Mink
VIP Alumni
VIP Alumni

Hard to answer, if you cut the link and link and loose L2 connectivity STP will need to re-calculate and elect an new root and underlying switches will recalculate their path and cost to it and decide which path is preferred.  You would need to give us a bit more information on the topology.  however is you have no redundant paths then you dont have to worry about loops.

 

what I would try to figure out, is, if you are going to kill the link, can you predict what switch will become root, because if you leve it to chance the wrong one (lowet prio) will be elected, or even based on mac.

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Both these locations have only one switch each. the switch at Office-B1 will be cut off from the Main office switch.

So, both these switches will act independent. 

 

Both of these (at present) do not have any other switches attached , though Main office switch has a router connected to it.

 

Will the stp recalculation cause loss of connectivity in this case?

 

in that case, you will not have an issue, as there is no spanning tree paths on a single switch.

 

I would however advise you to start naming your VTP domain and make the one switch the server. and possibly add a password to the vt domain, this way its more scalable for future expansion and will prevent someone plugging a switch in and taking over as VTP server by accident and screw up your vlans (believe me i have seen this happen)

Please remember to rate useful posts, by clicking on the stars below.

Joseph W. Doherty
Hall of Fame
Hall of Fame
If you have multiple switches within the same STP domain, cutting an active inter-switch link causes a STP re-convergence event. The impact varies on your topology and STP variant being used.

I think (?) for just two switches, the switch that's the current root won't impact its other ports. The non-root disconnected switch will become its own root switch, and that one might block all its ports while it does. With just one switch losing its connection to the root switch, I would expect its STP root election would proceed rapidly - likely best (i.e. fastest) if using a "rapid" STP variant.

I would expect similar (likely minimal) impact for the converse too, i.e. the disconnected non-root switch regains its link to the original root and yields its root status.

If using a rapid STP variant, with only two switches, impact might be so minimal, no clients might notice. Without a rapid STP variant, some clients may notice.
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