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Joining two STP loops - need some help

Occasional Contributor

Joining two STP loops - need some help

Got the run around from HP call in support so I am reaching out in the forums.


I have two buildings - each running STP loops. Plant 1 is running Instance 1 and Plant 3 is running Instance 3. They work fine. Now it is time to put a redundant link between the two plants. I added Instance 3 to my core switch that sits in Plant 1. Although it looked to be working, I had one vlan not routing properly inside plant 1 and VoIP quality was suffering between the two plants. I rolled back the changes and disabled the redundant link port on my core switch and everything was fine again.


I once ran across a document showing th ecombination of MSTP loops but can't find it again. Know this can't be that difficult but Just can't find an easy answer. 


Part of the issue is I have the same vlans being used in both loops and HP will only let one instance handle a vlan. Can't put it in both instances.


Any help would be appreciated.

Respected Contributor

Re: Joining two STP loops - need some help

MSTP has some specific rules, and the common use case is to have half the VLANs (eg odd-numbered) in instance 1, and the other half (eg even-numbered) in instance 2. This is usually done in conjunction with a gateway redundancy protocol like VRRP.


Perhaps the simplest thing to do is not have any instances and just put both buildings into the common instance (CIST). It isn't clear if that would be appropriate or suitable for your environment and requirements though.


There is reference to a doc "How to configure Multiple Spanning-tree (MSTP) on HP ProCurve switches" that may be useful (you may have more luck finding the PDF online).