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Webcast-Catalyst9k
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VLANs lost from VLAN Database

Hi Everyone,

I have a Cisco 3560 switch with 4 vlans configured. I plugged in another cisco switch to a trunk port. The new switch didn't have all the vlans configured yet. On my main switch I lost 2 vlans from the vlan database.

Can someone explain why this happened ? I'm guessing it was to do with VTP ?

Cheers

Peter.

3 REPLIES

Re: VLANs lost from VLAN Database

Hi Peter,

VTP servers advertise their VLAN configuration to other switches in the same VTP domain and synchronize their VLAN configuration with other switches based on messages received over trunk links. VTP server is the default mode.

Make the 2nd switch in vtp client mode.

After making switch 2 in client mode it willl not advertise so the 4 vlans on the main switch remain intact.

set vtp mode server (default)

set vtp mode client

You can configure a switch to operate in any one of these VTP modes:

Server-In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters, such as VTP version and VTP pruning, for the entire VTP domain. VTP servers advertise their VLAN configuration to other switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode.

Client-VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

Transparent-VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2.

Off (configurable only in CatOS switches)-In the three described modes, VTP advertisements are received and transmitted as soon as the switch enters the management domain state. In the VTP off mode, switches behave the same as in VTP transparent mode with the exception that VTP advertisements are not forwarded.

Hope it can resolve your issue.

Kind Regards,

sachinga@hcl.in

New Member

Re: VLANs lost from VLAN Database

Firstly when the new switch must have been configured, u might hav configured in VTP server mode and then connected to N/w,

Later you might have removed VLans

this made 2 vlans deleted from main switch

then you had changed it to Client,

This caused it to propogate in network

Re: VLANs lost from VLAN Database

Read the section on "Configuration Revision Number" in the following document:

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094c52.shtml

The newly introduced switch likely had a higher Configuration Revision Number, and resulted in a change to the pre-existing VLAN database.

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