VLAN Trunk Protocol
was created by Cisco Systems
to administrate network traffic
over designated VLAN trunk links (links that carry traffic for more than one VLAN). With VTP, a system administrator
can add, delete, and otherwise modify VLANs on a network. These changes are then propogated to the network switch
In addition to simple administration, VTP also enables VLANs to be trunked between networks of multiple types (Ethernet
, etc), as well as accurate tracking of VLAN traffic.
When implementing VTP on a network, a VTP server
is used to hand out VLAN information to switches. VTP information is only shared within a specified domain
. A switch can only be a member of one of these domains.
Switches can be configured to respond to VTP packets in one of three ways:
(default for Cisco Catalyst
switches) initializes the propogation of VTP information to all client
s in the domain.
is fairly self-explanatory. Switches operating in this mode can send and recieve VTP updates from servers, but cannot make changes to the VLAN information themselves.
: Switches in this mode are not active in the VTP domain (they do not update their own data with incoming information). Instead, they simply forward VLAN information out of all designated trunk links. Transparent switches can add and delete VLANs from their database, as the information is not shared with other clients, but, of course, these changes are significant only locally.