Wednesday, January 8, 2014

Troubleshooting VTP


If a switch doesn’t seem to be receiving updated information from a VTP server:

Either the swtich is in transparent mode. Verify by “show vtp status”

“there might not be a switch configured as vtp server”

The link between the switch and the other switches is not in trunking mode. VTP can be advertised only over trunk links. To verify if an interface is trunk or acess

“show interface type mod/num switchport

Make sure the vtp version is compatible with other switches in the VTP domain.

Make sure the VTP password matches in the vtp domain

Make sure the VTP domain name match that of the VTP server

VTP configuration


By default vtp mode is server, management domain is NULL, and there is no password.

If a switch receives a VTP summary advertisement on a trunk port from any other switch, it will automatically learn the VTP domain name, VLANs and the configuration revision number it hears.
Before you add a switch to the network, verify that the revision number is set to 0 “show vtp status”
There is two ways to configure VTP:
Global config mode
vlan database mode mostly deprecated
To join a specific VTP management domain, you have to “vtp domain domain-name
Configuring the VTP mode:
Server mode: multiple VTP servers can coexist in a domain. The servers do not elect primary or secondary, if one server is configured with a new VLAN or VTP parameter, it advertises the changes to the rest of the domain. All other servers synchronize the VTP databases to this advertisement just as any VTP client would
Client mode: if you want to configure a as VTP server, you start it as a client to learn the latest changes, than you configure it in server mode.
Transparent mode: this mode is used if a switch will not share the VLAN information with any other switch in the network. VLAN can still be created, deleted or modified, but they are not advertised, however VTP advertisement received by a transparent switch are forwarded out trunk links. Keeping switches in transparent mode can eliminate the chance for duplicate over-lapping VLANs in large network with many network administrators
vtp mode {server | client | transparent}
Vtp password password

On some IOS, you can turn vtp off, by using the command vtp off command. This command allows the switch to act the same as if it is in a vtp transparent with the addition that the switch doesn't forward vtp advertisement on trunk links.
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