Root bridge issue on 1GB links

[ohareka70]

Hello,

I have three Datacentres joined in a triangle with 1GB links in each direction.  Their are critical servers on each site.  The traffic is routed by VLANS on each site.  On one of my sites sw-BRET i would like to move the root bridge on VLAN2 and move it over to sw-BT

hostname sw-BRET

spanning-tree mode rapid-pvst

spanning-tree etherchannel guard misconfig

spanning-tree extend system-id

spanning-tree vlan 1-2,5-6,15,224 priority 0

spanning-tree vlan 4,13,201 priority 20480

spanning-tree vlan 200 priority 24576

hostname Sw-WEST

spanning-tree mode rapid-pvst

spanning-tree etherchannel guard misconfig

spanning-tree extend system-id

spanning-tree vlan 1-2,5-6,15,100,224,226,500 priority 4096

hostname sw-BT

spanning-tree mode rapid-pvst

spanning-tree etherchannel guard misconfig

spanning-tree extend system-id

spanning-tree vlan 100,226,500 priority 0

I can afford for this to go wrong or cause any downtime. Can anyone see any obvious reason why i shouldnt do this or why it would work etc?

The reason i ask for this is that a server in sw-BT datacentre is copying backups from vlan 1 (server 1) to vlan 2 (server 2).  But both servers sit in the sw-BT datacentre.  So the server 1 goes up the 1GB link to sw-BRET because sw-BRET is the root bridge for vlan 2 and copys the data back down the link again.  If i just moved the root bridge for vlan 2 to the same datacentre namely sw-BT my problem would be solved.

any advice appreciated

regards,

Kevin

[lmediavilla · Accepted solution]

The best way to move the root bridge is with root primary, but your setup is priority 0 so the macro root primary won't work

I would do it this way

SW-WEST

spanning-tree vlan 2 priority 12288

SW-BRET

spanning-tree vlan 2 priority 8192 ! to keep it as the backup root

Until now we have downtime of 0

Now the change

SW-BT

spanning-tree vlan 2 root primary

in no more than two seconds a better bpdu will be sent by switch BT and switches will send a TCN (topology change network) and the topology change will be almost instant

kind regards

[ohareka70]

Thanks for the advice - sounds good to me.

[cadet alain]

Hi,

The best way to move the root bridge is with root primary, but your setup is priority 0 so the macro root primary won't work

I disagree, the best way is to set the priority to zero manually and not with the macro because the macro will take a look at the actual situation and won't adapt to future situations but as zero is the lowest priority it will always win.

Regards

Alain

Don't forget to rate helpful posts.

[lmediavilla]

If you already have a 0 you will not be able to migrate fast, whatever you use I wouldn't recommend to setup the root bridge to priority 0 so you will be stuck if you want another switch to take over the root bridge, the macro as you said gets a value after listening the bpdus, you can use it or use a value but please don't use 0 because you will be stuck whenever you want to do a change of the root bridge.

cheers

[cadet alain]

Hi,

then in this case you raise the priority of this switch and lower the one you want as root to zero.

if you used the macro then you would have to lower the other one priority as well so just one command on actual root bridge in addition but at least you know that this won't be taken away by any other switch.

What is the disadvantage of that additional step vs the security advantage ?

Regards

Alain

Don't forget to rate helpful posts.

[lmediavilla]

The only think I wouldn't use is 0 for the root bridge, otherwise you will be stuck if you want to move the root bridge.

Cheers

[paul driver · Accepted solution]

Hello

Cadet Allan is correct - using the stp root macro isn't as good as manually setting the root priority as the current root bridge could be overwritten much easier by just applying a switch with the same macro command which unfortunately has a lower bid value.

Spanning-tree vlan xxx priority x

I personally think is a much safer alternative


Res
Paul


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