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Spanning-tree root and secondry priorities

BilalButt62333
Beginner
Beginner

As we know we can make a root primary and root secondary of all VLANs of some VLANs with two switches but my concern is can we use the same priorities values for different VLANs for making root primary and secondary on the different switch or on the same switch which are already primary or secondary for some other VLAN

for example:

SW1:

spanning-tree vlan 1,20,30 root primary

spanning-tree vlan 1,20,30 priority 4096

 

SW2:

spanning-tree vlan 1,20,30 root secondary

spanning-tree vlan 1,20,30 priority 8192

spanning-tree vlan 40 root primary

spanning-tree vlan 40 priority 4096

SW3:

spanning-tree vlan 40 root secondary

spanning-tree vlan 40 priority 8192

 

I have implemented it in the cisco packet tracer no issue occurred but if we use this scenario in a real production environment is this way ok?

 

1 Accepted Solution
8 Replies 8

one point only 
when you set the SW as root primary the priorty is auto change to be lower from all SW for that VLAN, 
I see here you set root primary then manually set priority??

well now I understand after reading the article you provided two main ways manual priority or just giving the primary, and secondary command. S if only go for manual priority then my scenario is ok as mentioned below?  

SW1:

spanning-tree vlan 1,20,30 priority 4096

 

SW2:

spanning-tree vlan 1,20,30 priority 8192

spanning-tree vlan 40 priority 4096

SW3:

spanning-tree vlan 40 priority 8192

Yes, that's fine, if using PVSTP.

BTW, regarding using numeric priority values vs. symbolics, the problem with the latter, different Cisco switches sometimes use different values for "root" and/or "secondary", which can lead to unexpected results.

Also, BTW, I prefer to not explicitly assign the lowest (highest priority) value just in case I need to temporarily override the current root switch (without needing to reconfigure it).

Yes true, making root primary and root secondary is alot better and fast
option than set numerical priority specially in big network where alot no
of switches.

"" Cisco switches sometimes use different values for "root" and/or "secondary""
just to mention here the SW not use different value, the process is SW see what is lower priority use in STP domain and adjust the value to be lower than it, that why we see different value for priority in different case. 

So it's mean better than confusion we should prefer root primary and root
secondary instead of numerical values specially when many vlans are
available right?

I do this small lab, 
i config IOU1 to be root primary and IOU2 to be secondary 
and all fine you see that IOU2 and IO3 show that IOU1 is root of this domain.
Screenshot (9).png
Screenshot (10).png

then I add new SW IOU4 with priority 4096, here the root SW must keep it role BUT NO 
the IOU4 with lower priority win the election even if I config root primary in IOU1.

that why I prefer config lower or as @Joseph W. Doherty mention not lower but one bit higher i.e. 8196.

this will protect root from any new SW have low priority,

friend this is my view to issue, and for you you are have more info. about your network.

 

Screenshot (11).pngScreenshot (12).png

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