VTP password and other wierdness

I was working through INE’s Vol 3 workbook tonight and thought I would do VTP. This should have been a very simple topic to master – there are not too many commands and it is a very simple technology.

Although as many of you will know to be treated with care as it can destroy your network in one foul swoop. This is why in all the places I have worked we turn it off.

So I started off with my 4 switches wiped with clean config and setup a few trunks to connect them all together.

Configured SW1 as the server and the others as clients and for some reason SW4 was just not getting the vlan’s

How to troubleshoot VTP

The first command is sh vtp status
SW1#sh vtp status
VTP Version                     : 2
Configuration Revision          : 10
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 17
VTP Operating Mode              : Server
VTP Domain Name                 : CISCO
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0xE3 0x60 0xB3 0x97 0x29 0xF2 0xE0 0xA9
Configuration last modified by 0.0.0.0 at 3-6-93 08:15:08
Local updater ID is 0.0.0.0 (no valid interface found)

There are a few interesting things here that I have found.

1. Ensure all switches are running the same version of vtp. Although the switch will say VTP Version 2 this does not mean it is running version 2 you need to ensure VTP V2 mode says enabled – if not put your switch into server mode and type vtp version 2

For some reason one of my switches says VTP Version : running V2

not sure why that is – will look into it.

So all your switches are running the same version. Still not vlans appearing

check the VTP password.

This is another strange one as the vtp password does not show in the config

To check type sh vtp password
SW1#sh vtp password
VTP Password: cisco
SW1#

I did this on all switches and one switch SW4 did not have the password set, I set the password and everything worked.

Remember that all the vlan data is not stored in the running-config but in a file in flash called vlan.dat
SW1#sh flash:

Directory of flash:/

2  -rwx     7963038   Mar 1 1993 00:44:13 +00:00  c3560-advipservicesk9-mz.122-25.SEE2.bin
3  -rwx        1304   Mar 6 1993 08:15:08 +00:00  vlan.dat
4  -rwx        3002   Mar 6 1993 02:08:32 +00:00  config.text
5  drwx         192   Mar 1 1993 00:06:00 +00:00  c3560-ipbase-mz.122-25.SEB2
358  -rwx          24   Mar 6 1993 02:08:32 +00:00  private-config.text

If you want to erase a switch completely you need to delete this file or else when you clear the config and reload the vlans just come back.

One last thing is debugs

If you are still getting nowhere
SW1#debug sw-vlan vtp ?
events      vtp events
packets     vtp packets
pruning     vtp pruning events
redundancy  vtp redundancy
xmit        vtp packets transmitted

Ok now all that is working on to Mixing VTP modes

Cisco Documentation explains it so well:

Understanding VLAN Trunk Protocol

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Roger Perkin - CCIE #50038 is a Network Automation Engineer & CCIE Consultant based in the UK, currently working for Softcat Plc as a Senior Network & Security Consultant.
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