VTP Pruning

Can a root bridge be pruned out of a VLAN? I can't find a definitive answer as most texts assume that a root bridge would have active ports.

Thanks

Dave

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    Well...  VTP and STP are two entirely different things...  STP needs to
    have active ports in order to run, and the VLAN must exist.  Trunk
    links count here.



    In VTP Pruning, however, it's specifically looking at access ports
    and/or SVIs.  So if you had neither of those, you would prune it.  The
    question becomes whether pruning kills spanning tree operations, or
    whether it signals to a switch to simply not send anything.



    While I've never paid attention to it when labbing things up before
    with pruning on switches, I do remember that as soon as you exclude a
    VLAN from pruning it would resume operation (example of VTP Transparent
    + pruning in between client/server switches).  The fact that it did so
    immediately tells me that spanning-tree was working all along, and
    didn't need to recalculate anything.



    So from that point of view, you can have any vlan pruned including one
    on a root bridge, but it won't affect spanning tree.






     



    Scott Morris, CCIEx4
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    dbeattie wrote:

    Can a root bridge be pruned out of a VLAN? I can't find a
    definitive answer as most texts assume that a root bridge would have
    active ports.

    Thanks

    Dave







    Internetwork Expert - The Industry Leader in CCIE Preparation

    http://www.internetworkexpert.com



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  • Thanks for that, Scott.

    So if I have a single line of 4 or more switches trunked together with only the end two active in a VLAN and vtp pruning enabled, how do the intervening switches know that they will have to not prune the VLAN in order for the first and last switches to communicate?

    Regards,

    Dave

  • If they're exchanging VTP messages (client/server) then you don't need to do anything.  Voodoo magic solves it.

    If you have the middle guys in transparent mode, but still pruning, then you'll need to use "switchport trunk pruning vlan remove (#)" to remove the VLANs you don't want pruned.

    HTH,

    Scott







    ----- Original Message -----
    From: "dbeattie" <[email protected]>
    Sent: Wed, June 17, 2009 7:31
    Subject: Re: [CCIE R&S] VTP Pruning


    Thanks for that, Scott.

    So if I have a single line of 4 or more switches trunked together with only the end two active in a VLAN and vtp pruning enabled, how do the intervening switches know that they will have to not prune the VLAN in order for the first and last switches to communicate?

    Regards,

    Dave



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  • Scott. Excellent. Thanks. Dave

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