Please answer a VTP question

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If a VTP client switch is added to the domain, and this client has a
revision number that is higher than the current server switch,  why
does the new switch's configuration get propagated to the server and

I know how revision number works, and that you should make sure that
the server has the highest number before adding a new switch.

But I thought the whole point of server-client relationship was to
determine who got to give out new info?

Re: Please answer a VTP question

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Clients can't originate new configurations. However, if the newly added
switch was a VTP server, it would overwrite the configs on the other
switches, including VTP servers with lower revision numbers.

Lars Christensen
CCIE #20292

Re: Please answer a VTP question
I found the slide in the curriculum that got me confused.

"There is one VTP server switch, S1, and two VTP client switches, S2
and S3.

          /      \\
        S2      S3
                      S4 (new switch)

S4, which has been previously configured as a VTP client, is added to
the network. The revision number of the switch S4 is 35, which is
higher than the revision number of 17 in the existing network. S4
comes preconfigured with two VLANs, 30 and 40, that are not configured
in the existing network. The existing network has VLANs 10 and 20.

When switch S4 is connected to switch S3, VTP summary advertisements
announce the arrival of a VTP-enabled switch with the highest revision
number in the network. The animation shows how switch S3, switch S1,
and finally switch S2 all reconfigure themselves to the configuration
found in switch S4. As each switch reconfigures itself with VLANs that
are not supported in the network, the ports no longer forward traffic
from the computers because they are configured with VLANs that no
longer exist on the newly reconfigured switches."

Why does this happen, if S4 was a client?

Re: Please answer a VTP question
On 27 May 2009 21:00:16 GMT, Lars Christensen

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So when a new client is inserted into a network, it can't mess things
up?  The server will propagate the VTP info to it?

Re: Please answer a VTP question

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To sum up the words:

- vtp mode server:
Switch originates the VTP messages to all switches with a lower revision
number. If other switches in the network is configured as server, the
server with the highest revision number wins. If you introduce a new
switch into an existing network and it is configured as server, you could
therefore end up in a situation, that the newly installed switch actually
overwrites the current VLAN database in the network by fault.

- vtp mode transparent:
Switch passes the VTP messages through without learning the VTP message.
This type is also needed to use extended VLANs (above 1005)

- vtp mode client:
Switch will learn VTP messages from any server with a higher revision
that the latest VTP database installed. The switch cannot originate VTP
messages, but will learn and pass through the messages.

Hope this clarifies your question

Lars Christensen
CCIE #20292

Re: Please answer a VTP question
I started the CCNP track this week, beginning with BCMSN, and it
beautifully clarified all things VTP.

Also a very good review for the upcoming CCNA exam.

Re: Please answer a VTP question
On Thu, 28 May 2009 09:29:06 -0500, Mitch@_._ wrote:

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agreed - except the default setting is VTP server (or used to be)....

anywhere with a reasonabley paranoid change control regime will not
like the idea of "1 mistake can melt the network" - which is exactly
what you can get with VTP.

And now we have the latest WAN technology VLPS (bridging) - so you can
actually manage to melt a complete set of campus networks.....

so - the most important VTP setting is "transparent" cos then it is
effectively turned off.

Regards - replace xyz with ntl

Re: Please answer a VTP question

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I'm curious why there's no direct command to manually reset the
revision number?  I know there are ways to make it reset, but why no

Re: Please answer a VTP question
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Setting to transparent mode resets the revision number to zero (amongst
other things). This setting will remain if you then switch back to client

FWIW I just went on a CCNA course and the instructor, a guy with plenty of
real world experience, said that even when a switch is in client mode, it
will propogate its vlan config on joining a network, provided of course it
has the highest revision number.

IMO safest thing would be to wipe all config off the switch, then set to
transparent mode before adding it to the network.

Re: Please answer a VTP question
On Fri, 12 Jun 2009 04:37:08 +0100, "Vaughan Butler"

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Yes, I finally came across multiple sources that confirm that, so I
feel solid there.

Re: Please answer a VTP question
Dnia 5/27/2009 11:00 PM, Lars Christensen wrote:
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Have you tested your answer in a lab? Do this, or look at this flash,
Switch in client mode CAN override VLAN database - it will be prompted
for new vlan database by the server, which will then do the disaster.

Pozdrawiam @ Mariusz Trojanowski @@@ slotyzmok @ narod!ru  (s <-> z)
"U nas się na wszelki wypadek jednemu i drugiemu odrąbuje głowę. Nuż
który urządzał zamachy albo w ogóle ciskał bomby." [Burzliwe życie
Lejzorka Rojtszwańca]

Re: Please answer a VTP question

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Hi Mariusz

Watching the flash file, I get a bit confused as the flash file kind of
contradict some of the ideas behind the client/server mode in VTP. I
haven't tried it the lab, but it might be interesting to do. I'll have to
test it before I can conclude on this issue.


Re: Please answer a VTP question
I've got my CCNA exam schedules for next Tuesday.  

So much information.  Root bridge.  Designated router.  VTP. STP. It's
like soup in my brain.

I really need to cram extended ACLs.  The syntax is very confusing to

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