What is VLAN Trunking Protocol – VTP ? Explained with Examples

By | 9th November 2015

What is VLAN Trunking Protocol (VTP)?

During the early days of networking, it was difficult to implement VLANs across networks. Each VLAN was manually configured on each network switch. Managing a large switched network used to be a complicated task, VLAN trunking methods were developed to help ease this problem.

VTP Concept

VLAN Trunking Protocol (VTP) is a Cisco Proprietary which basic aim is to manage all configured VLANs across a switched network.  VTP helps to propagate and maintain VLAN configurations consistency to other switches on the network.

VTP is a messaging protocol that uses layer 2 trunk frames to add, delete and rename VLANs on a single domain. It helps to centralize changes which are sent to other switches in the network.

A switch had to be configured in the role of a VTP server to manage your VLAN configuration on your network. The server(s) will share VLAN information with other switches on the network which must use the same domain name.

VTP learns only normal-range VLANs (VLAN IDs 1 to 1005).

The primary role of VTP is to maintain VLAN configuration consistency across a network administration domain.

 VTP stores VLAN configurations in the VLAN database called vlan.dat.

After a trunk is established between switches, VTP advertisement is exchanged between the switches. Both the server switch and client exchange and monitor advertisement from one another to ensure each has an accurate record of VLAN information. VTP advertisement will not be exchanged if the trunk between the switches is inactive.



                                        vtp2

In the diagram above, a trunk link is configured between switch S1, (VTP Server), S2 and S3 – VTP client.

After a trunk is established between the switches, VTP summary advertisement is exchanged among the switches.

How to Configure VTP on a Cisco switch

VTP Configuration Guidelines

The following command is used to configure a switch (S1) as VTP server:

Sw1#config t

Sw1(config)#vtp mode server

Sw1(config)#exit

Configure switch (Sw2 and Sw3) as  VTP client:

Sw2#config t

Sw2(config)#vtp mode client

Sw2(config)#exit

Configuring VTP Domain Name and Password:

For VTP summary advertisement be exchanged among the switches, all switches in the network have to belong to the same domain and use the same password:

VTP Domain

Sw1#config t
Sw1(config)#vtp domain lab
Sw1(config)#exit

VTP password

Sw1#config t
Sw1(config)#vtp password orbit123
Sw1(config)#exit

Configure the same domain name and password for the clients.

Confirm configuration changes.

Use the show vtp status command on S1 to confirm that the VTP mode and domain are configured correctly.

Sw1#show vtp status

VTP Version : 2

Configuration Revision : 0

Maximum VLANs supported locally : 64

Number of existing VLANs : 5

VTP Operating Mode : Server

VTP Domain Name : lab

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x8C 0x29 0x40 0xDD 0x7F 0x7A 0x63

Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00

Confirm the same for S1 and S2

To verify the VTP password, use the show vtp password command.

Sw1#show vtp password

VTP Password: orbit123

S1#



VTP Pruning

 VLAN Configuration

 VLAN ID Ranges

 VLAN Switch Port Membership

 Voice VLAN Configuration

VTP Modes of Operation

Host Standby Router Redundancy Protocol (HSRP)

Virtual Router Redundancy Protocol (VRRP)

Gateway Load Balancing Protocol (GLBP)

Spanning Tree Protocol (STP)

IPv6

EIGRPv6

RIPv6 or RIPng

OSPFv3

DHCPv6

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