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 tasks, VLAN trunking methods was developed to help ease this problem.
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 on the network.
A switch had to be configured in the role of a VTP server to manage your VLAN configuration on your network. The sever(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.
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
The following command is used to configure a switch (S1) as VTP server:
Sw1(config)#vtp mode server
Configure switch (Sw2 and Sw3) as VTP client:
Sw2(config)#vtp mode client
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:
Sw1(config)#vtp domain lab
Sw1(config)#vtp password orbit123
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
Voice VLAN Configuration