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Thread: VTP debugging

  1. #1
    Join Date
    Aug 2011
    Location
    Plano, TX
    Posts
    92

    Default VTP debugging

    This was my real-life VTP debugging session this weekend:

    I was asked to add a new switch to an existing VTP domain. No problem, says I, I’ve done this a million times while prepping for my CCNA and at work.

    So I bolt the switch into the rack, hook up the console and clear the config (including the vlan.dat file). I set all the admin stuff like passwords, ip address (all the it equipment in this domain are in management VLAN 12), etc and configure the switch as a VTP client. I check the port on the server switch and make sure it’s set for 802.1q trunking and do the same on the new client switch, then I make sure the new switch is at VTP rev 0. I hook them up with a cross-over cable (I don’t need one, because I’m GbE-to-GbE, but I like to use one whenever I’m staying in the same layer). Then I wait for the VLAN’s to download, and… nothing. That’s weird, because I’ve done this lots and lots of times. Both ports are up/up and CDP shows the server switch is connected, but Vlan12 is down/down.

    Now I turn on VTP event debugging and I can see the VTP events come through, but no Vlan12. It’s getting late on Saturday (and I work for free on Saturdays apparently). Finally I notice at the end of the VTP event debug the message “MD5 mismatch”. Okay, now I’ve got something to fix. I type that into Google and voila! all-knowing Google says the VTP passwords are not the same. Oh-oh. I inherited this particular VTP domain, the original IT guy is long gone, I never use VTP passwords in my VTP domains and I have no idea what the password is.

    Back to Google and it’s so simple: “show vtp password” on the server. I set the VTP password on the new switch and down come the VLAN’s and up goes Vlan12!

    Lesson learned.
    Bob Dempsey
    CCNA

  2. #2
    Join Date
    Jun 2010
    Location
    Right here
    Posts
    460

    Default

    Very nice....would be a nice lab for the text book!!!

    Thanx for the nice tip!
    A+, Network+, CCNA, CCNP/Data Center wannabe
    A spark of encouragement can ignite great endeavors

  3. #3
    Join Date
    Mar 2008
    Posts
    2,888

    Default

    LOL - yep been there late one night and things look odd.

    It is a nice idea to use VTP passwords.
    Maddox Thomas-Clark 14/10/2008
    Bean Thomas-Clark 18/09/2007
    Big Evils Cisco World
    Linkedin

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