VTP problem between two 2950 switches

Answered Question
May 7th, 2007

Hello.After connecting two 2950 switches with an ether channel and setting the ports in channel-group and port-channel interface as trunks as I have seen it done in previous configurations in our network I have the following problem with VTP between them.

When I set one switch as VTP server and create VLANs on it the other switch picks up those VLANs even though no VTP domain name is set on it.I was under impression that a switch couldn't get VLAN information from another switch if they aren't in the same VTP domain.Is there something I'm missing here?

I have this problem too.
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Correct Answer by ankbhasi about 9 years 8 months ago

Hi Friend,

This is an expected behavior what you mentioned in your second post.

By default, the switch is in the VTP no-management-domain state until it receives an advertisement for a domain over a trunk link or until you configure a domain name.

If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and the VTP configuration revision number. The switch then ignores advertisements with a different domain name or an earlier configuration revision number.

So as you mentioned you deleted everything and when it came back again it has no-management-domain and as it receuved the VTP advertisement it inherits the VTP domain name and start working in same VTP domain name. But if you manually change the VTP domain name on both the switches then any changes in vlan configuartion will not be propogated and updated by second switch.

HTH

Ankur

*Pls rate all helpfull post

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ankbhasi Mon, 05/07/2007 - 07:00

Hi Friend,

Can you paste the "sh vtp stat" from both the switches?

Regards,

Ankur

IgorHamzic Mon, 05/07/2007 - 07:15

1st switch(the one configured with the VTP domain name):

VTP Version : 2

Configuration Revision : 3

Maximum VLANs supported locally : 64

Number of existing VLANs : 8

VTP Operating Mode : Server

VTP Domain Name : Proba

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x43 0x7F 0x81 0xF0 0xEF 0x07 0x59 0xEF

Configuration last modified by 0.0.0.0 at 3-1-93 01:14:18

Local updater ID is 192.168.200.1 on interface Vl1 (lowest numbered VLAN interface found)

2nd switch(the one set without VTP domain name):

VTP Version : 2

Configuration Revision : 3

Maximum VLANs supported locally : 250

Number of existing VLANs : 8

VTP Operating Mode : Server

VTP Domain Name : Proba

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x43 0x7F 0x81 0xF0 0xEF 0x07 0x59 0xEF

Configuration last modified by 0.0.0.0 at 3-1-93 01:14:18

Local updater ID is 192.168.200.2 on interface Vl1 (lowest numbered VLAN interface found)

Another interesting thing is also happening.I disconnected the 2nd switch from the 1st one,deleted vlan.dat and removed the domain name and then reloaded it.I checked the vtp status after reload and it seemed all right(not in the same VTP domain,no VLAN's on it) but when I connected the switches again the 2nd one again picked the VLANs and what's more interesting the VTP domain name.

jliow Mon, 05/07/2007 - 07:13

Hi there

in this case, both are VTP servers, just that one was defined earlier with proper VTP domain and the other is not yet configured.

When you trunk them, the later switch will read all the VLAN information that is passed between,

However, with proper VTP domains set, you can only edit the vlans on the master switch, which is the VTP server switch you have configured.

IgorHamzic Mon, 05/07/2007 - 07:23

So even though they are not in the same VTP domain the 2nd switch(the one not configured with VTP domain name yet) will pick up the VLAN information and VTP domain name from the configured switch because they are trunked together and set VTP domain name on itself.That seems weird to me.

Correct Answer
ankbhasi Mon, 05/07/2007 - 07:46

Hi Friend,

This is an expected behavior what you mentioned in your second post.

By default, the switch is in the VTP no-management-domain state until it receives an advertisement for a domain over a trunk link or until you configure a domain name.

If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and the VTP configuration revision number. The switch then ignores advertisements with a different domain name or an earlier configuration revision number.

So as you mentioned you deleted everything and when it came back again it has no-management-domain and as it receuved the VTP advertisement it inherits the VTP domain name and start working in same VTP domain name. But if you manually change the VTP domain name on both the switches then any changes in vlan configuartion will not be propogated and updated by second switch.

HTH

Ankur

*Pls rate all helpfull post

IgorHamzic Mon, 05/07/2007 - 09:21

Thanks for the extensive explanation Ankur.It really helped me.

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