Spanning-Tree force root bridge election

[mikemanz83]

My regards,

What is the best for the switch to always win a Root Bridge Election in STP,  set spanning-tree priority 0 or set spanning-tree root primary ??

Thanks 

[Reza Sharifi]

Spanning-tree vlan vlan-id root primary

example:

Spanning-tree vlan 50 root primary

HTH

[mikemanz83]

hello my friend, i mean with the question, what is best to configure to forcing the sw to be the root bridge priority 0 or root primary?

[Reza Sharifi]

Hi,

I personally like to use the root primary command as it is more intuitive and easier to manage when you issue "sh run" 

This way you know what switch is root and what is a backup.

HTH

[Giuseppe Larosa]

Hello @mikemanz83 ,

as far as I know the spanning-tree root primary is just a macro that will use fixed values for base priority , and what is more important it is not able to react in the future if someone attempts to connect a  switch with a lower STP priority.

So I prefer to use for PVST or Rapid PVST

spanning-tree vlan 1-4094 priority 0 to be sure to make the device the root bridge primary now

spanning-tree vlan 1-4094 priority 4096 on the backup secondary root bridge.

I think the macro uses values like 8192 and 16xyz for primary and secondary allowing space for root bridge pre-emption at a later time if someone uses the base prioroty of 0 or 4096.

Hope to help

Giuseppe

[balaji.bandi]

what device is this "you do not need set command" (may be if i recall old CAT os?)

Setting prioty also works, if both have same priorty again it has decision process, so best to do primary and secondary, but you can also achieve if you setting priority.

add to other post below can help primary and secondary.

spanning-tree vlan X  root primary   ( X is the VLAN to be root on this switch)

spanning-tree vlan X root secondary ( X where you look for secondary of the primary not available)

[MHM Cisco World · Accepted solution]

priority and mac address, 
if you config priority equal to 0 BUT if other SW also by mistake config with same value then the tie breaker is mac but if the new mac address is best then it will elect as root.
so config root primary is best because it will elect the SW as root whatever other SW will config.

[mikemanz83]

Thanks for that answer my friend, thats what i was thinking but i wanst sure....but thanks for make it clear for me!

Also thanks to all that took the time in aswer my question!!

[paul driver]

Hello
I would suggest to define a priority numeric value and NOT use the macro PRIMARY/SECONDARY as it isn’t deterministic enough, Once this command is set it does not dynamically change after that as such if for some reason your need the decrease the stp priority value it doesn’t change automatically its value is set as to when it was first applied, It is only applicable to the current existing stp estate as when you applied the command.

[mikemanz83]

Many thanks my friend, i will build a lab to test that!!