VTP overwrite question - Does it affect active links

[brianhill88]

Hello,

Let's say I have two switches (switch A and B).  Switch A currently has VTP enabled and is mode server.  It has VLANs 1 to 50.  Switch B is not currently VTP enabled but has VLANs 1 to 10 manually created.  There are active hosts in VLANs 2-10 on switch B.

My question is this.  If I enable VTP on switch B in client mode, do the hosts lose connectivity temporarily when the vlan database is overwritten even though they are being overwritten with some of the same VLAN numbers?  I know the interfaces will retain their configuration.  I'm just not sure if there is a service interupption.  My guess would be yes but I have not had time to test this in a lab environment.

Thanks

(Switch A is a 6509 and Switch B is a Nexus 7000.  When we first received the Nexus 7000, VTP was not supported).

[paul driver]

Hello,

VTP Client mode CAN overwrite the vtp database if the revision number is higher than the current vtp server/client.

And if the "new" vtp server/client doesn't have the same vlans in it database than the "old" vtp server/client has then YES you will lose connectively to the hosts in the vlans which will be unfortunately.deleted.

To save guard against this, you can change the revision number to zero then you will be safe to proceed.

The easiest way to do this is to change the vtp mode to transparent and back to server or client on the "new" vtp switch before adding it to the existing vtp domain.

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[brianhill88]

I don't think you read my question.  This isn't about whether or not the the database is going to be overwritten or if the client will overwrite the server (i know how to safe guard against that).  My question is whether or not I will lose connectivity even thought the vlans are being overwritten with the same VLAN numbers.

[InayathUlla Sharieff]

Hi Brian,

Straight answer to your question would be that there will not be any distruption in the network if you have brand new switches with no privious configuration on it and this was the only conifg which was configured.

NOTE: Things to remember in VTP to avoid any distruption in/to the network:

=====================================================

-> Before adding any new switch to the existing domain make sure the revision number is set to 0. ( Cnfigure Switch to Transparent mode as this will set the config register to 0 and then configure the vlans appropriately on switch .

In your setup following things to be check:

===========================

1-> On Switch A check the show vtp status and note down the current config revision number.

2- > Switch B check the VTP status here as well. If the revision number is lower than Switch A then you are good to go. If in case its higher you will have to face the music, hence the best recommendation is to change the vtp mode to transparent as this will set the config regis value to 0 and avoid all the possible loss.

3-> Now configre the VTP domain name, and mode as Client. you should be good to go.

HTH

Regards

Inayath

*Plz rate all usefull posts.

[Joseph W. Doherty · Accepted solution]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

As long as the VLANs are there both before and after Transparent to Client mode transformation, I wouldn't expect a host impact.  I've done this kind of change on production devices (not Nexus, though) but generally during a maintenance window so I hadn't really noticed whether there was a host impact.

[brianhill88]

Thanks for actually answering the asked question Joe  ; )

We have a maintenance window for this but my concern is that some things (backend storage) are very sensitive to even momentary loses of connections.

I think people see VTP in the title and rush to paste information about clients overwriting servers.

I'm going to setup two test switches and try this.  I'll come back and update this thread with the results.

Thanks

[InayathUlla Sharieff]

HI Brian,

Hope you should not have any problem. AS we all have tested this earlier hence based on those experience we suggested.

Anyways its a good idea when you have test switches to do the same. please keep us updated and let us know if we can be of any help for you.

Regards

Inayath

[paul driver]

Brian,

I did interpret your original post incorrectly, and apologies for that, but I did have a valid point.

The vtp database of the 2^nd switch had been modified, thus if you wasn’t aware of vtp synchronisation either in server or client mode, then potential to overwrite the vtp database was there.

Everyone on here, including myself uses their own personal time to try if possible assist others in any networking queries or issues they may have, but your comment in response to my post was  unwarranted,sarcastic and not appreciated.

[brianhill88]

Hello,

I setup a test environment consisting of a 3750 and a 3560.  The 3750 was setup as VTP Server with VLANs 1 -10. It had one laptop in VLAN 5.  The 3560 was setup with no VTP and VLANs 1-5 created manually.  The 3560 also had a laptop setup in VLAN 5.  I then trunked the two switches together and then ran persistent pings between the two laptops.  Next I enabled VTP mode on the 3560 in transparent mode.  Finally I switched from transparent mode to client mode.  It updated the VLANs so that the 3560 now has VLANs 1-10 also.  I did not lose any pings between the two laptops on different switches.

pdriver - I apoligize if I offended you.  I did use a "winky face" in my post to show that I was being humorous.  I do appreciate the people who take the time to come here and contribute to a beneficial community, yourself included.

[InayathUlla Sharieff]

HI Brian,

thanks for the update. Yes as we all stated to you about the same that you will not have any impact in carrying out this activity.

Regards

Inayath