What is VLAN Trunking Protocol (VTP)?
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol used in network management. It simplifies the administration of VLANs, which is especially useful in large networks with numerous switches.
Here’s an overview of its key aspects:
Purpose and Functionality:
Centralized VLAN Management: VTP allows network administrators to manage all VLANs from a central switch and have the changes propagate to other switches in the network automatically. This centralization reduces the need for manual configuration on each switch.
Consistent VLAN Information: It ensures that all switches in the VTP domain have consistent and up-to-date VLAN information.
VTP Modes:
Server Mode: In this mode, switches can create, modify, and delete VLANs for the entire VTP domain. Changes made on a server switch are propagated to all other switches in the VTP domain.
Client Mode: Switches in client mode cannot create, change, or delete VLANs. They receive VLAN information from server switches and forward this information to other switches.
Transparent Mode: Switches in transparent mode do not participate in the VTP domain but will forward VTP advertisements through their trunk ports. They can create, modify, and delete VLANs, but these changes are local to the switch and are not propagated to other switches.
VTP Advertisements:
VTP uses advertisements to distribute VLAN information among switches. These ads are transmitted as multicast frames over trunk links.These multicast frames contain information about the VLANs present in the network, their names, and their assigned VLAN IDs. Switches use this information to dynamically update their VLAN databases and ensure consistency across the network.
VTP Domains:
A VTP domain consists of switches controlled by the same administration and sharing a common VTP environment. Each switch belongs to a single VTP domain, and VTP details are only exchanged among switches within the same domain.
In a VTP domain, switches communicate using VTP advertisements to share VLAN information such as VLAN IDs, names, and other attributes. This allows for consistent VLAN configuration across all switches within the domain, making it easier to manage and maintain the network. Additionally, changes made to the VLAN configuration on one switch are automatically propagated to other switches in the domain, ensuring consistency and reducing the potential for misconfigurations.
How VTP works
After a trunk is established between switches, VTP advertisement is exchanged between the switches. Both the server switch and client exchange and monitor advertisements 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
VTP Configuration Guidelines
The following command is used to configure a switch (S1) as a 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 to 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# shows 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#
In Summary
VLAN Trunking Protocol (VTP) is a protocol developed by Cisco that is used to manage VLAN configurations across a network of switches. VTP allows for centralized management of VLANs, making it easy to make changes that will automatically be applied to all switches within the VTP domain.
There are three modes of operation in VTP: Server mode, which allows for the creation, modification, and deletion of VLANs; Client mode, which can receive information but cannot make changes to VLAN configurations; and Transparent mode, which passes VTP information along without making changes to its own VLAN configuration. This protocol helps to simplify configuration and ensure consistency across a network, reducing the potential for errors and minimizing administrative overhead.
VTP Prunin VLAN ConfigurationVLAN ID Ranges
VLAN Switch Port Membership Voice VLAN Configuration VTP Modes of Operation
Spanning Tree Protocol (STP) IPv6 EIGRPv6 RIPv6 or RIPng OSPFv3
