VTP Transparent switch is getting vlan propagate from VTP servr in database

Unanswered Question

Hi Champs,

I have a Core switch attached to a distribution switch. The Core is acting as VTP server, where as the distribution switch is configured as a Transparent VTP. As per my knowledge Transparent is suppose to show or carry only its own vlan. But here i am getting the default 5 vlan (1, 1002, 1003 1004, 1005) in Transparent mode additional to that there is one more vlan (17-OST vlan) which is getting propagate from VTP server which has total 15 vlan and OST vlan 17 is one of them.

Question: what kind of configuration or setting VTP require to have a vlan propagated from VTP server, when a switch is working on VTP transparent mode?

Your reply will be appreciable in this regard.

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Overall Rating: 4 (1 ratings)
Jon Marshall Wed, 01/30/2008 - 03:59
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vlans 1, 1002 -> 1005 are default vlans that you will find on any switch so these have not been propogated by VTP. - oops, sorry you have already said this in your post.

Vlan 17 - are you sure this was not configured manually on your VTP transparent switch. if you have 15 vlans in total on your VTP server and only one vlan - vlan 17 is on your VTP transparent switch then i don't think your transparent switch is updating it's vlan information from the vtp server.


Kevin Dorrell Wed, 01/30/2008 - 04:42
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Is it possible that VLAN 17 was created on your server before this switch was put into transparent mode?

If a switch is in server or client, it will learn VLANs from the server, provided the server has a higher config revision. When you change that switch to transparent mode, it will keep the VLANs it had already learned from the server, and will use those as a starting position.

Maybe it was part of the domain at some point, then someone switched to transparent, and tried to delete all the learned VLANs, but missed 17.

Kevin Dorrell


Jon Marshall Wed, 01/30/2008 - 04:45
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Hi Kevin

That's what i thought but i tested on a 3560 and as soon as you put the switch into VTP transparent mode it automatically writes the vlan info into the running config. And the running config posted does not show vlan 17.

So i'm a little confused at the moment.

To the OP, what switch type and what IOS are you running.


Kevin Dorrell Wed, 01/30/2008 - 04:50
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That's interesting. I had always wondered why some postings show VLANs in the config and some don't. Also, I had always wondered where a transparent switch keeps its VLANs, and the answer seems to be "in the config" from your observation. I didn't think it was in the vlan.dat, 'cos once the VTP becomes transparent the vlan.dat no longer gets updated.

I am watching this thread with great interest.

Kevin Dorrell


Please have the Show version output below:

Cisco Internetwork Operating System Software

IOS (tm) C3500XL Software (C3500XL-C3H2S-M), Version 12.0(5)WC17, RELEASE SOFTWARE (fc1)

Copyright (c) 1986-2007 by cisco Systems, Inc.

Compiled Tue 13-Feb-07 15:04 by antonino

Image text-base: 0x00003000, data-base: 0x00352924

ROM: Bootstrap program is C3500XL boot loader

Switch uptime is 26 weeks, 3 days, 18 hours, 11 minutes

System returned to ROM by reload

System restarted at 14:44:22 EDT Sat Jul 28 2007

System image file is "flash:c3500xl-c3h2s-mz.120-5.WC17.bin"

cisco WS-C3524-XL (PowerPC403) processor (revision 0x01) with 8192K/1024K bytes of memory.

Processor board ID FAB0534Q29V, with hardware revision 0x00

Last reset from warm-reset

Processor is running Enterprise Edition Software

Cluster command switch capable

Cluster member switch capable

24 FastEthernet/IEEE 802.3 interface(s)

2 Gigabit Ethernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.

Motherboard assembly number: 73-3904-11

Power supply part number: 34-0851-02

Model revision number: A0

Motherboard revision number: D0

Model number: WS-C3524-XL-EN

Configuration register is 0xF

This is done on a fresh switch, i mean this setup has newly installed switches, so there is no point of existing vlan database on the switch prior to it's transparent mode and also the name of vlan is same what i m getting on the server.

Thnx guys for your response, please let me know if you guys need anymore information .

bilousand Wed, 01/30/2008 - 05:19
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If I remember correctly 3524XL will show in config only VLANs from extended range (VLAN ID > 1005).

bilousand Wed, 01/30/2008 - 04:48
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If switch was attached to your network as server or client and then converted to transparent all VLANs existed at this point of time will remain in its database. Even reboot won't help as the transparent switch still reads its vlan.dat on start.

Kevin Dorrell Wed, 01/30/2008 - 04:51
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So are we perhaps saying that the config holds a delta from the vlan.dat? The way to test that would be to isolate the switch, put it back into server, then reboot it, and see if its vlan.dat comes up with the solitary VLAN 17.

I wish the vlan.dat were plain text.


bilousand Wed, 01/30/2008 - 04:54
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When a switch reloads, if the VTP mode or domain name in the VLAN.DAT file and the startup-config file differ, the switch uses only the VLAN.DAT file's contents for VLAN configuration.

So converting to transparent implies delete flash:vlan.dat

bilousand Wed, 01/30/2008 - 04:58
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Even though vlan.dat isn't plain text you can briefly extract its content

more flash:vlan.dat


000000D0: 00000000 00000000 00000000 08564C41 .... .... .... .VLA

000000E0: 4E303030 32000000 00000000 00000000 N000 2... .... ....


Kevin Dorrell Wed, 01/30/2008 - 05:16
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Hey, that's cool! I had to add the /ascii switch to stop my terminal going mad, but that gives me a good start on decoding the contents.


Kevin Dorell



In regards to the implied delete falsh:vlan.dat...what is the harm of doing that if the switch is in VTP transparent mode? I have a switch that is in the same state as the original posters due to it once being in client mode in the VTP domain. It is now in transparent mode but the propogated VLAN info is still there and I wan to get rid of it. I can't see any way to remove the vlans from the vlan.dat file? Any help would be appreciated.




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