MST (Multiple Spanning-Tree Protocol)

 

I am bit confiused about MST and need some clarification

 

Is it always a best practise to tie VLAN 1 (untagged in most production network) to Instance other than default instance 0 (CST) when using MST as choice or layer 2 loop prevention protocol.  I found youtube video on this topic and he does not really go deeper into this. Please advise

I am very new in networking and going for CCIE so if my question does not make sense, forgive me

av

Comments

  • Sorry about previous post. I forgot to give you an example

     

    For instance

     

    I have vlan 1 as default untagged vlan in the network

     

    All Access switches directly connects to Core with two links per switch

    switchA-----2x 1gig copper----Core

    switchB---2x 1gig copper-----Core

    switchc---2x 1gig copper--Core

    ALL THESE switches have 100 Vlans as example. If you look at the topology there is litteraly one spaning tree instance is needed since all edge switches directly connects to core with redundant links

     

    In this case, I want to setup MST instead of running 100s of spanning tree instances per vlan and group them into two instances i.e

     

    spanning-tree mst configuration

      name TEST

    revision 1

     instance 1 vlan 1-50

    instance 2 vlan 51-100

    spanning-tree mode mst

    spanning-tree mst 1 priority 0

    spanning-tree mst 2 priority 0

     

    I AM NOT TOO SURE AOBUT MAPPING VLAN 1 to instance 1 or if I should leave it default instance 0

  • In my experience, I leave VLAN 1 in instance 0. I create as many instances as I deem appropriate. Remember that for every instance of MST you have a BPDU is sent, the instance # increments the priority, 32768 by default. So Instance 0 will have a priority of 32768, instance 1 will be 32769 and so on. 

    I don't by best practice place VLAN 1 into anything other than instance 0. I have also only worked in 2 environments where MST is used, the IT Managers at both companies had their CCNPs. RSTP is by far the majority that I have seen for commonly sized networks of 10-100 Vlans. MST is good in really large L2 networks with 100+ VLANs. Both companies had 150+ VLANs so it was appropriate. 

    At the end of the day it is ultimately a preference. MST and RSTP do pretty much the same things, RSTP is just easier for most people to work with. 

    HTH
    Rob



    On Thursday, July 16, 2015 1:40 PM, avashi1 <[email protected]> wrote:


     

    I am bit confiused about MST and need some clarification

     

    Is it always a best practise to tie VLAN 1 (untagged in most production network) to Instance other than default instance 0 (CST) when using MST as choice or layer 2 loop prevention protocol.  I found youtube video on this topic and he does not really go deeper into this. Please advise

    I am very new in networking and going for CCIE so if my question does not make sense, forgive me

    av



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  • makes sense.. I guess for interoperability reasons, leaving untaggld/native vlan to default 0 would be best option. 

  • It has nothing to do with interoperability. Cisco sends all control plane traffic via VLAN1. If VLAN 1 is the native then it is untagged. I never leave VLAN 1 as the native VLAN if I can help it. I always use a different VLAN. In practice I use VLAN 999 or 1999 as native. VLAN 666 is unused ports. 

    My recommendation for starting out, start with lower level CCNA stuff. You said it yourself, your new to networking, which tells me you don't have that deep hands on experience yet. Start with CCNA, getting the cert is up to you, go through the content and then move onto CCNP. I tried to make the leap from CCENT to CCIE, holy crap dude, way too much way too quick. I used to email Brian McGahan daily, he finally gave me the advice to take a few steps back and go through CCNA and CCNP. I grabbed the certs along the way to show progress. I think you would be much better off starting there instead of trying to hit the CCIE head on. I've been working on my CCIE for 3 years now. I've had my CCNP for 18 months, I am constantly learning new things. I have taken the lab 2 times, this last time I got the dread pass/pass/pass overall fail. Hopefully my third attempt will be the "third times the charm"

    good luck to you, remember it's not a sprint, it's a really long marathon with lots of hurdles, rough patches, nasty weather and above all, frustrations when you don't get something. 



    On Thursday, July 16, 2015 2:27 PM, avashi1 <[email protected]> wrote:


    makes sense.. I guess for interoperability reasons, leaving untaggld/native vlan to default 0 would be best option. 



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  • 90% of the production network will have vlan 1 as default. I understand using vlan 999 as default/native/untagged  for security reasons. You dont have to use vlan 999. You can use vlan 1 as native as long as vlan is not routed or configured as layer 3 (svi interface). Regardless, thats not what I am asking you Riker. 

    Dont worry about my approach to ccie. I am looking for an answer regarding MST and vlan 1 mapping to instance 0. 

  • Also guys

     

    This was my cpu results Before putting switch from default PVST to MST on 100 vlans. Both switches are configured in VTPv3 for VLANs and MST. MST digests matches on both switches

    ## BEFORE ###

    SW1# show process cpu sorted 5min | in 200

     200       17707     13025       1359  0.63%  0.76%  0.28%   0 Spanning Tree 

     

    ### AFTER ###

     

    SW1#show process cpu sorted | in 200

    200       16551     11914       1389  0.00%  0.00%  0.05%   0 Spanning Tree 

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