Please answer a VTP question

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.

Regards,
Lars Christensen
CCIE #20292

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.


             S1
          /      \\
        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?

On 27 May 2009 21:00:16 GMT, Lars Christensen




Thanks.

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?

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

Regards,
Lars Christensen
CCIE #20292

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.

On Thu, 28 May 2009 09:29:06 -0500, Mitch@_._ wrote:



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

stephen_hope@xyzworld.com - replace xyz with ntl

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
command?

Setting to transparent mode resets the revision number to zero (amongst
other things). This setting will remain if you then switch back to client
mode.

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.

On Fri, 12 Jun 2009 04:37:08 +0100, "Vaughan Butler"



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

Dnia 5/27/2009 11:00 PM, Lars Christensen wrote:


Lars
Have you tested your answer in a lab? Do this, or look at this flash,
http://www.cisco.com/warp/public/473/vtp_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 siê na wszelki wypadek jednemu i drugiemu odr±buje g³owê. Nu¿
który urz±dza³ zamachy albo w ogóle ciska³ bomby." [Burzliwe ¿ycie
Lejzorka Rojtszwañca]

$1@inews.gazeta.pl:



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.

Regards
Lars

I've got my CCNA exam schedules for next Tuesday.  
I'M SCARED!  :)

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
me.