CCNA Extra Lesson 01: VTP (VLAN Trunking Protocol) Concept and Configuration

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Overview of the VTP in Networking

"" Can you imagine that you have hundreds of Cisco Switches among your networks and you have huge amount of VLANs, that you have to provisioning to among of those switches.? What will you have to do when the you have to configure all of the VLANs manually.? ""

So, to reduce the burden of provisioning VLANs on switches, CISCO came up with this solution: VTP – VLAN Trunking Protocol.

VLAN Trunking Protocol (VTP) is a Cisco proprietary Layer 2 protocol that helps manage VLAN configuration consistently across a network of Cisco switches. Instead of manually creating, deleting, or renaming VLANs on every switch, VTP allows you to configure VLAN information on one switch (the VTP server) and automatically propagate those changes to all other switches in the same VTP domain.

It’s like having one “control center” for VLAN management in your network.

How VTP Works

VTP messages are sent over trunk links (such as IEEE 802.1Q or ISL) to share VLAN information between switches.

When a switch in a VTP domain receives VLAN information from another switch with a higher configuration revision number, it updates its VLAN database automatically.

VTP Main Components

1. VTP Domain

a. A common group of switches that share VLAN information.

b. All switches in a domain must have the same VTP domain name.

   2. VTP Modes

a. Server Mode

                  i. Default mode.

                  ii. VLANs can be created, modified, and deleted.

                  iii. Changes are advertised to all other switches in the VTP domain.

                  iv. Stores VLAN information in NVRAM.

b. Client Mode

                  i. Cannot create, delete, or modify VLANs locally.

                  ii. Receives and applies VLAN updates from VTP servers.

                  iii. Stores VLAN information in RAM (lost on reboot).

c.  Transparent Mode

                  i. Does not participate in VLAN synchronization.

                  ii. Can create VLANs locally, but changes affect only that switch.

                  iii. Forwards VTP advertisements to other switches.

3. VTP Advertisements

a. Sent every 5 minutes or immediately after a VLAN change.

b. Types:

                i. Summary Advertisements – contain VTP domain name and configuration revision number.

                ii. Subset Advertisements – contain actual VLAN details.

                iii. Advertisement Requests – sent when a switch needs an updated VLAN list.

c. Configuration Revision Number

                   i. Incremented every time a VLAN change is made on a VTP server.

                   ii. If a switch receives an update with a higher revision number, it overwrites its VLAN database. Because the highest configuration revision number is generally defined as VTP Server.

                   iii. Warning: If you connect a switch with a higher revision number but outdated VLAN data, it can erase VLANs across the domain.

                   iv. VTP switches use an INDEX number known as a configuration revision number to keep track of the most recent information in the VTP Domain.

                   v. The advertisement always starts with the configuration revision number that is 0 (Zero)

4. Requirements for VTP

  • Must be trunk between Switches
  • Must be configured the same domain name
  • Password must be same for all switches at the same domain.

VTP Versions

  • VTP Version 1 -- Default version; supports only Ethernet VLANs.
  • VTP Version 2 – Supports Token Ring VLANs and consistency checks.
  • VTP Version 3 – Supports Private VLANs, extended VLAN range (1006–4094), and better authentication/security.

VTP Pruning

VTP pruning is a feature in Cisco's VLAN Trunking Protocol (VTP) that optimizes network bandwidth by preventing unnecessary VLAN traffic from being forwarded across trunk links.
To configure VTP pruning, this must be enabled on all the switches in the VTP domain. By default it is disabled and to enable VTP prunnng use “vtp pruning enable“.

VTP Advantages

  • Centralized VLAN management.
  • Reduces misconfigurations.
  • Saves time in large networks.

VTP Disadvantages / Risks

  • A wrong configuration revision can wipe VLANs network-wide.
  • Requires consistent domain names and passwords.
  • Not useful in networks with only a few VLANs or where VLANs are highly localized.

How to Configure VTP in Cisco Network


Step-01: Server Switch Configuration

//VLAN Configuration
Server(config)#vlan 100 
Server(config-vlan)#name ITD
Server(config-vlan)#vlan 200 
Server(config-vlan)#name SCM
Server(config-vlan)#vlan 300
Server(config-vlan)#name MCD
Server(config-vlan)#vlan 99
Server(config-vlan)#name MGMT
Server#show vlan brief 

//VTP Configuration as Server
Server(config)#vtp domain cisco
Server(config)#vtp mode server 
Server(config)#vtp version 2 
Server(config)#vtp password cisco 
Server#show vtp status

//Trunk Port Configuration
Server(config)#interface gigabitEthernet 0/1
Server(config-if)#description Trunk_Port
Server(config-if)#switchport mode trunk 
Server(config-if)#switchport trunk native vlan 99 
Server#show interfaces trunk 

Step-02: Transparent Switch Configuration

//VTP configuration as Transparent
Transparent(config)#vtp version 2
Transparent(config)#vtp domain cisco
Transparent(config)#vtp mode transparent 
Transparent(config)#vtp password cisco
Transparent#show vtp status 

//Trunk Port Configuration
Transparent(config)#interface range gigabitEthernet 0/1-2
Transparent(config-if)#description Trunk_Port
Transparent(config-if)#switchport mode trunk 
Transparent(config-if)#switchport trunk native vlan 99 
Transparent#show interfaces trunk 

Step-03: Client Switch Configuration


//VTP configuration as Client
Client(config)#vtp version 2
Client(config)#vtp domain cisco
Client(config)#vtp mode client 
Client(config)#vtp password cisco
Client#show vtp status 

//Trunk Port Configuration
Client(config)#interface gigabitEthernet 0/1
Client(config-if)#switchport mode trunk 
Client(config-if)#switchport trunk native vlan 99
Client#show interfaces trunk 
Client#show vlan brief 

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