Troubleshooting

VTP Wiped My VLANs (Revision Number Explained)

VSVipul Sir · 6 min readLast updated: 22 July 2026

A switch joining the domain with a higher VTP configuration revision number overwrites every other switch's VLAN database — even if it is a server you just plugged in from the lab. The revision number, not the switch role, decides who wins. This is the classic way to erase a production network in seconds.

What you see

%SW_VLAN-6-VTP_DOMAIN_NAME_CHG: VTP domain name changed to CAMPUS.
%SW_VLAN-6-VLAN_DELETED: VLAN 10 was deleted by VTP.
%SW_VLAN-6-VLAN_DELETED: VLAN 20 was deleted by VTP.

Why it happens

VTP synchronises the VLAN database across switches in a domain. Every change increments a configuration revision number. When a switch receives an advertisement with a higher revision than its own, it accepts that database wholesale — deleting any VLAN not present in it.

The trap: a switch used for testing may have a very high revision number. Plug it into the production domain and, because its number is higher, every production switch adopts its (nearly empty) VLAN list. Being in client mode does not protect you — clients propagate revision numbers too.

How to confirm it

show vtp status
show vtp counters
show vlan brief

show vtp status shows the Configuration Revision. Before connecting any switch to a live domain, check this number.

The fix

! Reset the revision number to zero before connecting a switch:
! either change the domain name and change it back...
vtp domain TEMPORARY
vtp domain CAMPUS
!
! ...or put the switch in transparent mode (revision is forced to 0)
vtp mode transparent
!
! Safest default for most networks today
vtp mode off

Switching to transparent mode sets the revision to 0 and stops the switch participating. For most modern networks, VTP transparent or off is the correct permanent setting.

How to stop it happening again

Make vtp mode transparent part of your standard build for every new switch, and always run show vtp status before connecting hardware that has been used elsewhere.

Questions people ask

Does client mode protect my VLANs?

No. A VTP client with a higher revision number will still overwrite servers. Mode does not decide the winner — the revision number does.

How do I reset the VTP revision number?

Change the VTP domain name to something else and back again, or set the switch to transparent mode. Both reset the counter to zero.

Reading the fix is not the same as doing it

Every fault on this page can be broken and repaired on real Cisco routers and switches in our Ahmedabad lab — which is how it stops being theory. Come and see the rack before you pay anything.