VTP (VLAN Trunking Protocol)
By Stephen Bucaro
A VLAN (Virtual LAN) allows a network administrator to partition a LAN to conform to
the business functions of the organization without physically modifying the network.
A VLAN is created by configuring some ports on network switches to be in the same
broadcast domain. Other ports on the network switches can be configured into a different
VLAN by configuring them into their same broadcast domain.
If a port on a network switch is connected to another switch, it is called a trunk
and can carry multiple VLANS. Devices on one VLAN can't see the devices on a different
VLAN without going through a router. Based upon the 802.1Q standard, the data frames
of each VLAN are identified by a 12-bit tag, allowing 4,096 different VLANS on the same LAN.
VTP (VLAN Trunking Protocol) is a Cisco proprietary protocol that advertises the VLAN
configuration through all the switches in a domain. This allows an administrator to
configure VLANs on a single VTP server, easing the administration of a network.
VTP operates in three modes:
In Server mode the VTP server can receive and send advertisements within the entire
VTP domain. An administrator can create, modify, and delete VLANs and other configuration
parameters for the entire VTP domain. When you make a change to the VLAN configuration
on a VTP server, the change is transmitted out all trunk connections.
In Client mode an administrator can receive VTP advertisements from other switches
and learn the VLAN configuration of the network, but cannot send VTP advertisements and
so cannot create, change, or delete VLANs.
In Transparent mode an administrator can create, delete, and modify VLANs, but
the changes are not transmitted to other switches in the domain, they affect only the local switch.
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