Spanning tree vlan root primary on B-series, C-series, K-series, N-series, S-series

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Hi, maybe is a silly or complex question but ...

Recently we discovered an issue on our data center network where a vlan suffered connection loss; as we found it was all caused by an old switch that was automatically elected as root primary for the affected vlan. We proceded to configure our core chassis to be primary root at the mentioned vlan and problem was solved. the core switch is non enterasys/extreme and the old switch was a very old enterasys switch. probably the old switch dont had the ram/cpu/forwarding capacity to be a root on any vlan !!! 

Now, the thing is that i want to make sure that all of my remote sites ( that are almost completely enterasys/extreme based ) had the appropiate settings in order to ensure that the most capable enterasys/extreme switch onsite is primary root and not had the issue of a slow switch performing as primary root.

how can it be done ?  thanks in advance....
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Francisco Garcia

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Posted 2 years ago

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Eric Burke

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Not sure if there is a simple way to do this (other than dropping the priority on those you want as root bridge).  The problem you found is pretty common.  Since the MAC address is used to judge when they're set to default, it's often the oldest units that end up with the lowest MAC.  Hopefully someone can provide a better method of setting them all simply...
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Erik Auerswald, Embassador

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Hi Francisco,

you need to set the STP priorities of the switches you want to have as root (both primary and secondary).

You should always use compatible STP version. Per-VLAN spanning tree implementations available from different vendors are non-standard and only partially compatible with other spanning tree implementations, both standard and non-standard. A good choice is MST, which is standard, broadly supported across vendors, and downwards compatible with both the older standards, original and rapid spanning tree protocols.

Erik
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Francisco Garcia

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thanks Erik. please let me ask you if by setting prioirities you mean to lower those for something like "0" ??? . so that's essentially what Glyn is stating on this same thread.  You've been very helpful...
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Erik Auerswald, Embassador

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Hi Francisco,

yes, you should use a priority of 0 for the root switch, and priority 4096 for the secondary root switch.

Erik
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Francisco Garcia

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Thanks for your insight
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Straw, Glyn, Employee

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Hi Franciscoo,

Out of interest , are all the old edge switches on default priority settings ? if they are then as long as you have set the priority on the root bridge to for example ,zero then there is no way that you will have an issue with root bridge election. If someone has manually changed the priorities then there is a chance that they could be same as root bridge and then it will be lowest mac , which is the older device normally that becomes root. Really checking the priority configurations are consistent is the only way to be sure this doesn't happen.

There is also a feature called restricted role which may help you but this is not supported on all the listed products. See the information below:

https://community.extremenetworks.com/extreme/topics/spantree-root-guard-implementation-on-eos-devic...

Hope this helps
Best Regards
Glyn
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Francisco Garcia

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Thanks Glyn...