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While trying to create a new VLAN on a switch stack (that has many VLANs and many interconnected switches) I get an error about the switch not being the primary server for VLAN database. When running the exec command "show VTP status" the switch shows up as 'VTP Operating Mode: Server' and all other switches that I can access show up as client.

First question is: If there is a switch elsewhere in the network that I can't see that is also a server, will I break or screw up the VTP or VLAN database if I set this switch to 'Primary?'

The way I've been reading the documentation, all of the switches in the network default to "Server Secondary" and in order to make configuration changes to the VTP or VLAN database, one of those switches needs to be temporarily set to "Server Primary" via the EXEC command "VTP Primary." After making the configuration changes (i.e. adding a VLAN) the system will eventually reset that primary server back to secondary status.

Second question is: Is my understanding of the functionality described in the above paragraph accurate?

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You can see the primary server (if any) in the output of show vtp status:

Primary ID                        : 0011.2233.4455
Primary Description               : primary-switch-name

If the Primary ID is 0000.0000.0000, then your current switch does not recognize any primary server, including itself. To answer your questions:

  1. When you try to promote a switch to the VTP primary server role, VTP performs a sanity check to make sure no other switch on the network if already the primary, and will warn you if one is found. Either way, IOS will prompt you to proceed, so you can still back out if you're unsure. This is important, because the new primary server will cause all other VTP clients and servers to overwrite their existing VTP configuration with that of the new server. However, only switches in the same VTP domain and with the same password would be affected, and you would be able to see those with show vtp devices.

  2. I think you have it mostly correct. The one part I would comment on is that the only time a primary server demotes itself to secondary status is when it rejoins the VTP domain after a reload. During normal operation, a primary server will remain the primary server unless you run vtp primary on another server.

If you have only one switch configured as the VTP server, and it is not primary, I would conclude that it was rebooted at some point, which would have caused it to demote itself. It should be safe to promote it back to primary. If you're ever unsure, back up your VLAN database (typically flash:vlan.dat on smaller platforms) before making changes, so you can switch to transparent mode and restore your VLANs quickly if you need to.

Cisco has a comprehensive document on VTP Version 3 that goes over all of this and more.

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  • This a fantastic response James, thank you much! – Ejoso Jan 28 '14 at 21:55
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    Glad I could help! – James Sneeringer Jan 28 '14 at 21:56

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