spanning-tree root command

I've got a couple dozen switches and noticed the root is the furthest, slowest switch on the network. If I change the root to the core will this cause a convergence and cause all switches to "listen/learn/forward" on all ports?

Basically I'm asking if I should wait for an outage window to make the core the root :p

Reply to
Wil Schultz
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I dont' know, let me know what you find out:-)

I suspect that STP does not do anything like force all ports blocking. It will just keep on doing its thing on a port by port basis.

If you make the change by lowering the priority of the new root then it might be faster than raising the priority of the existing root.

- In the lowering the priority of the new root case.

New root knows that it has a better priority than the existing root and sends bpdus on all ports. Remember that when you switch on a bridge it assumes that it is the root at first. If inferior bpdus are received then it decides to stop being root and begins to flood received bpdus from the root out over the network. I give in now.

- In the raising the priority of the old root case. New root has to time out it's non-rootness and decide to become root. All the bridges will do this in fact.

No more time now. Would be interesting to find this out.


I wouldn't do such a thing in a production situation.

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You can expect spanning-tree to reconverge if a new root advertises. Unless you are using 'rapid spanning-tree', 'uplink / backbone fast', spanning-tree portfast etc. then expect an outage ... expect one anyway. I would never make a major spanning-tree topology change like that during production hours. Too much to lose for little gain (no comms problems during production hours is an expectation not a benefit ).


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I would definately do this during a scheduled maintenance window. Also you can set the spantree priority on your core switch so that it will be the root bridge and remember to do the secondary so that you can always predict spantree reconvergence.

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You can always blame any interruption on "TELCO"


Reply to
John Agosta

Well, I waited for an "informal" outage window :-)

! spanning-tree portfast bpduguard spanning-tree portfast default ! errdisable recovery cause all errdisable recovery interval 30 ! spanning-tree vlan 1-99 root primary diameter 7 !

Issued the above and didn't miss a ping!


Wil Schultz wrote:

Reply to
Wil Schultz

Sorry I missed this, but that matches with out experience - moving the root doesn't cause any kind of outage.


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