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I was wondering how VTP protocol deals with revision conflict?

E.g. VTP clients and servers are up to date with the latest database revision X.

Suddenly two VTP servers propagate revision X+1 with conflicting changes in it.

How is that solved?

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How is that solved?

Probably not really at all.

https://www.cisco.com/c/en/us/support/docs/lan-switching/vtp/98155-tshoot-vlan.html#topic14

(quoted from above, emphasis by me)

VTP is designed for an administrative environment in which the VLAN database for the domain is changed at only one switch at any one time. It assumes that the new revision propagates throughout the domain before another revision is made. If you change the database simultaneously on two different devices in the administrative domain, you can cause two different databases to be generated with the same revision number. These databases propagate and overwrite the existing information until they meet at an intermediate Catalyst switch on the network. This switch cannot accept either advertisement because the packets have the same revision number but a different MD5 value. When the switch detects this condition, the switch increments the No of config revision errors counter.

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  • Agree that given explanation did not solve my question, but int the comments I received confirmation that two different databases would exist in the network. – kkris1983 Jul 24 '19 at 15:14
  • and what I read is using VTP ver.3 does not allow to cause the issue because of making choice for Primary VTP Server – kkris1983 Jul 24 '19 at 15:15
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If a switch gets revision X+1 from one VTP server, it will simply look at the revision number if that same revision number comes in an update from the other VTP server. The switch will then ignore the revision with the same number from the other server, thinking it is up to date.


Also, remember that it is not only servers, but also clients, that can propagate revisions, and it has been a problem in the past where plugging in a client with a higher revision number can and will wipe out the VTP database on all the switches in a network.

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  • I understand the problem with connecting a client to existing network but for this particular case lets forget it. But referring to your explanation it might happen that two revisions with the same number and different configurations exist in the network at the same time. Wouldn't it be an issue ? – kkris1983 Jul 23 '19 at 15:43
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    Yes, it's an issue. VTP is crap; it always has been. Every admin that has relied on VTP (or not known about it), has had it bite them. – Ricky Jul 23 '19 at 15:48
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    "Wouldn't it be an issue ?" Yes, of course. The problem is that the VTP database would not be consistent across all the switches. – Ron Maupin Jul 23 '19 at 15:49

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