Configuring a VLAN

Configuring a VLAN

VLAN Trunking Protocol (VTP) is a Layer 2 messaging protocol that maintains VLAN configuration consistency throughout a common administrative domain by managing VLAN additions, deletions, and name changes across multiple switches. VTP server updates are propagated to all connected switches in the network, which reduces the need for manual configuration (promotes scaling) and minimizes the risk of errors caused by duplicate names or incorrect VLAN types. VTP operates in server, client, or transparent mode. The default is server mode. VLAN updates are not propagated over the network until a management domain name is specified or learned.

VTP Example

The VTP server notifies all switches in its domain that a new VLAN, named ICND, has been added. The server advertises VLAN configuration information to maintain domain consistency.

VTP Example

Whenever a change to a VLAN occurs, the VTP server increments its configuration revision number and then advertises the new revision throughout the domain. When a switch receives the advertisement, it overwrites its configuration with the new information if the new revision number is higher than the one it already has.

VTP Advertisements

VTP advertisements are flooded over the factory default VLAN (VLAN1) every five minutes or whenever there is a change. The delete vtp command resets the configuration number.

VTP Modes

VTP operates in server, client, or transparent mode. The default is server mode. VLAN configurations are not advertised until a management domain name is specified or learned.

VTP Pruning

VTP pruning improves bandwidth by keeping unnecessary traffic from flooding the entire domain. By default, a trunk carries traffic for all VLANs in the VTP management domain. With VTP pruning enabled, updated traffic from station A is not forwarded to switches

Configuring a VLAN Summary

	VTP advertises and synchronizes VLAN configuration information.
	The three VTP modes are server (the default), client, and transparent.
	VTP messages include a configuration revision number. When a switch receives a higher configuration number, it overwrites its configuration with the newly advertised one.
	VTP pruning restricts flooded traffic to some trunk lines.
	VLAN 1 is the default VLAN configuration on the Catalyst 1900 switch.
	To configure a VLAN, you must enable VTP, enable trunking, create a VLAN, and assign that VLAN to a port.