MSTP...can we have many MSTI in Core Switch?

kronicklezkronicklez Member Posts: 40 ■■□□□□□□□□
Hi all,

Need your expertise regarding MSTI in MSTP. I already read the doc configuration regarding MSTP. Referring to that doc it just shows 2 MSTI only. Below is my network setup.

1.) 34 VC (EX4200) = 2 Vlan have in all VC and 2 VLAN different for each VC. In other word each VC have 4 VLAN. For example VC 1 (VLAN 101, 201, 136, 256), VC 2 (102, 202, 136, 256).

VC = one connection to Core 1 & one connection to Core 2. MSTI 1 (VLAN 101, 136). MSTI 2 (VLAN 201, 256)

2.) Core Switch (EX820icon_cool.gif

My Question can we made more then 2 MSTI. Core 1 Vlan 101, 136 will be primary. Core 2 Vlan 201, 256 will be primary. How about if i have 34 VC. I hope u understand my topology.



  • kronicklezkronicklez Member Posts: 40 ■■□□□□□□□□
    Hi all,

    Is there any one have experience deployment using MSTP in real environemnt? Still waiting someone comment. Thanks.
  • hoogen82hoogen82 Member Posts: 272
    Well.. I am not an expert with EX switching but hope my inputs help here...

    First off... I think you are trying to achieve Layer 2 Load Sharing by making certain vlan's primary on Core 1 and another Set on Core 2.

    To answer your question if whether we can more than 2 MSTI, yes you could do that... But this topology and the number of vlan's associated doesn't warrant more MSTI. But yes you could do that and add more vlan's to the VC in future.

    Now going back to what you described and the configuration, I am guessing that to be wrong. If VC1 has VLAN 101, 201, 136, 256 then all must reside in the same MSTI.. The bridge priority for that instance should be higher on core 1 and lower on core 2. Same thing for VC2 has VLAN 102, 202 .. they should have higher priority on Core 2 and lower on Core 1.

    That's how you distribute your load, remember MSTP is actually grouping many vlan's with a single instance of STP. The priorities of the bridge domain for the vlan's is what determines how they are distributed among the two switches.

    Also.. You still need to get L3 load sharing with vrrp....For all VC1 which has L2 path towards core 1, that's where you would want their priority to be higher for the gateway too using VRRP.


    P.S: Let me know the configuration, I probably could work with you a little here...
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  • unclericounclerico Member Posts: 237
    One thing to watch out for with MSTP is that you'll want to plan your topology in terms of vlans well in advance. The reason is if you add a new vlan after your MSTIs are configured the vlan hash will no longer match and you'll see blockages happen.
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  • kronicklezkronicklez Member Posts: 40 ■■□□□□□□□□
    Hi Hoogen,

    Thanks for your advise. Currently i'm in the middle of write config for deployment. I will post that config as soon as possible. Thanks for your input.
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