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How should I setup or design STP (spanning tree protocol) on our layer 2 network?

Posted on 2008-10-06
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How should I setup or design STP (spanning tree protocol) on our layer 2 network?

Do I enable STP only on our core switch?  Every switch?  Only distribution switches?  What is the appropriate design.......currently, one wrong move or patch, we will have a routing loop broadcast storm.

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Question by:ncvadf
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by:Interserv
ID: 22651755
Spanning tree is rather nice, because it is easy to set up.  You practically turn it on and walk away while it removes loops.

You would want spanning tree enabled on all switches.  STP will choose a root based on the lowest bridge ID.  The root switch is the master for spanning tree.  All of the non-root switches will build the shortest path to the root and remove any redundant routes.   Make sure the root is placed near firewalls or routers that are most used as the root will be the most used switch.  

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by:ncvadf
ID: 22651809
I guess that should have been the real question......Should our core switch be the root switch?
Also.....what if STP was only setup on a couple of switches?  Would we still get broadcast storms?
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src1963 earned 250 total points
ID: 22651838
ncvadf,

I don't have any specific knowledge of Procurve equipment but here are a few pointers:

1. If you don't have redundant links, ie. your switches are connected to a single central switch in a hub/spoke or tree fashion, you don't need STP.  

2.  if you have redundant links, i.e. there's more than one path between any two switches, you MUST run STP, or you will get broadcast storms.

3. If your using STP, it must be setup on ALL your switches.

4. No special configuration is required. STP will work without any special config on almost any network. Just enable it, allow default settings and your switches will do all the work. They will elect a root bridge and block all switch-to-switch paths that aren't needed to get to/from the root bridge automatically.  Even if you have multiple VLANs, this process will occur on each VLAN independently and in parallel.

5. For best performance, you should make sure that your most central switch, ususally the one that connects to your Internet router, is elected the root bridge. You can do this by setting the STP priority higher than the default on the switch you as your root switch.

6. By the way, once you enable STP, you will find it takes about 30 seconds for a switch to accept a new connection from a host - Be patient when connecting new hosts.





3. STP is pretty simple. The defaults work on almost any network structure.
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by:Interserv
ID: 22651943
The core switch should be the root and you would want to give that switch higher priority so others STP will choose it as the root.  Depending on where the switches are physically located you might not get broadcast storms.  Is there a reason why you wouldn't want to have STP on all of the switches?  
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