Change the root bridge

Unanswered Question
Jun 17th, 2010


If I'm to change our root bridge to be more central to our network (near our servers and users) should this be down out of hours, I'm not sure what problems this could cause?

What is the best way to change the root and re-converge?

I have this problem too.
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John Blakley Thu, 06/17/2010 - 07:10

On the switch you'd want to be root, you'd change the priority to 4096 (or multiples of 4096, but the lower number is higher priority. Default is 32768).

spanning-tree vlan 1 priority 4096

I'd create down time because your switches will recalculate best paths to the root after you change it. It'll cause a minor bit of downtime while doing this (may not, but I think it will).



Andy White Thu, 06/17/2010 - 07:48

What command can I use to locate the current root bridge?


Federico Coto F... Thu, 06/17/2010 - 07:51

On any switch, you do ''sh spanning-tree'' and it will show you the MAC address for the root bridge either Per-VLAN if using PVSTP or the root bridge of the entire layer 2 domain.

With the MAC address, you can locate the root bridge with the ''sh mac-address table''


John Blakley Thu, 06/17/2010 - 08:02

You can issue a "show spanning-tree"


  Spanning tree enabled protocol ieee

  Root ID    Priority    32769

             Address     0012.da9a.2a80

             Cost        8

             Port        1 (GigabitEthernet0/1)

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

OR "show spanning-tree root"

                                        Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001         32769 0012.da9a.2a80         8    2   20  15  Gi0/1

I'd then ping all of my switch IPs from that switch to get them in the arp table and then find the mac address of the switch that corresponds to the mac address that it's pointing to.




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