In an enterprise network with many interconnected switches, maintaining a
consistent list of VLANs across those switches can be administratively
cumbersome and potentially error prone. The VLAN Trunking Protocol (VTP) is
designed to automate this administrative task.
Switches that share
common VLAN information are organized into logical groups called VTP management
domains. The VLAN information within a VTP domain is propagated through trunk
links and is updated via the VTP protocol allowing all switches within a
particular domain to maintain identical VLAN databases.
Only
"global" VLAN information regarding VLAN number, name and description
is exchanged. Information on how ports are assigned to VLANs on a given switch
is kept local to the switch and is not part of a VTP advertisement.
These
are the attributes of a VTP Domain:
- A switch may be in only one VTP domain.
- A VTP domain may be as small as only one switch.
- VTP updates will be exchanged only with other switches in the same
domain.
- The way VLAN information is exchanged between switches in the same domain
depends upon the VTP mode of the switch.
- By default, a Catalyst switch is in the no-management-domain state until it
receives an advertisement for a domain over a trunk link, or until a management
domain is configured.