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Tonight I encountered something in my home lab I have never seen before. It had me puzzled for quite some time and frankly was driving me nuts. I finally just figured it out and had to share it with the world. Now, I am not fortunate enough to have access to any 3550/3560s yet, but I do have 4 2950’s connected in a square topology with fiber…enough to at least graze STP and many other things. Tonight I was going over the IPexpert switching VOD again, which involved some basic VTP.

My setup was simple: Make SW1 my VTP server, and make SW2-4 clients. Create some vlans on SW1, make sure they propogate…no big deal. Well, I was finding that every switch except for SW3 was working properly and I couldn’t put my finger on it.

I checked show vtp status at least 3 times… domain name matched, rev number on SW3 was lower than the server, all my trunks were up, VLAN 1 was not pruned… hmmmm, time for debugs!

I flipped on debug sw-vlan vtp events

VTP LOG RUNTIME: MD5 digest failing

It then showed me the calculated hash was different from the received hash…hmmm well I didn’t configure any VTP password or anything on any of the switches….aha! These switches must have been using VTP somewhere previously

I went into vlan database mode and did no vtp password followed by apply and exit just to be sure…poof magic! It started working. So, the moral of the story is that at least on the 2950 in my experience even if you are not running vtp passwords, you may still need to clear any old ones left in the vlan database

Hopefully this will save somebody else out there some headache, or better yet lab points!

Comments

6 Responses to “Random Fun Tip On VTP”

  1. fivedigits on August 21st, 2008 6:37 am

    Apologies if you did check this; your post didn’t mention it. In the ‘show vtp status’ output look for the line ‘MD5 digest’. This will tell you if you have a password configured. If you are using a password in your vtp domain you can then compare to other known-good switches to determine a mismatch.

  2. CCIE Journey on August 21st, 2008 9:32 am

    Anytime you start any fresh switching labs you will want to delete vlan.dat from flash or life gets interesting 😛

  3. tomek on September 4th, 2008 6:52 am

    I have the same symtops – MD5 incorrect – I add another vlan, the checksum was recalculated and everything start working :).

  4. nwlog on March 14th, 2010 5:37 pm

    VTP Kuriositäten…

    Bei der Integration eines 3560er Switches ist mir aufgefallen, dass die VTP Datenbank nicht aktualisiert wird. Eine Neukonfiguration nach dem löschen der vlan.dat oder eine Konfiguration via altertümmlicher ‘vlan database’ Methode konnte das Problem …

  5. dorjko on March 17th, 2010 11:05 pm

    thanks man. It works

  6. syed on September 2nd, 2010 2:25 pm

    thanks alot i was giving worng password which looked same and eventually my vlan was not coming up, after i cleared the vlan password and gave it back bingo it started working

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