Configure and Verify VLAN Trunking Protocol

Automate VLAN configuration and keep your switches perfectly in sync.

Imagine setting up a large office network with switches on every floor. Each department—HR, Sales, IT—needs its own VLAN to keep traffic separated and organized. Creating the same VLANs manually on every switch is time-consuming and error-prone. A typo in a VLAN name or number, or a forgotten switch, could cause problems.

Cisco created the VLAN Trunking Protocol (VTP) to solve this.

VTP operates at Layer 2 of the OSI model (the Data Link Layer) and automatically shares VLAN information among all switches in the same VTP domain. When you create, delete, or rename a VLAN on one switch, VTP sends that update to all other switches—keeping every device synchronized without manual configuration.

By the end of this lesson, you will be able to:

Discover what VTP does and why it helps manage VLANs easily.
Set up a VTP domain name so switches can share VLAN information.
Learn the three VTP modes: Server, Client, and Transparent — and what each one does.
Practice using Cisco CLI commands (in Packet tracer) to see how switches share and update VLANs in a network.

Understanding VTP

Imagine a large office building with multiple network switches — one on each floor.

Each floor has different departments (Finance, HR, Engineering), and each department should have its own VLAN for isolation and security.

If you had to manually create VLANs on each switch for every department, you’d be repeating the same configuration over and over again. This increases the chance of typos, inconsistencies, and wasted time.

VTP solves this by acting as an “information distributor.”

One switch acts as the VTP Server — it creates and manages the VLAN list.
Other switches can act as Clients, automatically receiving updates about VLANs from the server.
A Transparent switch ignores these updates but can still forward them to other switches.

Think of VTP as a company newsletter system:

The server writes and publishes the newsletter (VLAN updates).
The clients receive and read it (replicating VLANs).
The transparent switches simply pass the newsletter along without editing or reading it.

VTP Operation Modes

Mode	Description	Can Create/Delete VLANs?	Propagates VLANs?	Receives VLAN Updates?
Server	Default mode. Manages VLAN database and advertises VLAN information to the domain.	✅ Yes	✅ Yes	✅ Yes
Client	Cannot create, delete, or rename VLANs. Relies entirely on updates from servers.	❌ No	❌ No	✅ Yes
Transparent	Operates independently. Forwards VTP messages but does not synchronize VLANs.	✅ Yes (local only)	❌ No	❌ (does not update its own VLANs)

Lab Topology Overview

In this lab, you’ll need three switches connected with trunk links. Use the hostname command to rename each device before starting the configuration.

Switch1 — VTP Server
Switch2 — VTP Transparent
Switch3 — VTP Client

These switches are all part of the same VTP domain: ccnalab

Command Summary

Command	Description
`enable`	Enter privileged EXEC mode
`configure terminal`	Enter global configuration mode
`show running-config`	Display current configuration
`show vlan brief`	Display VLAN list, names, and ports
`show vtp status`	Display VTP configuration and mode
`vtp domain <domain-name>`	Set the VTP domain name
vtp version {1 \| 2 \| 3}	Set the VTP version (in Packet Tracer ver. 1 & 2 are available)
vtp mode {server \| transparent \| cliente}	Set the VTP mode
`vlan <number> [name <vlan-name>]`	Create or name a VLAN

Step-by-Step Lab

Task 1: Configure the VTP Domain

Goal: Set up a VTP domain called ccnalab on Switch1 and ensure all switches belong to this domain.

Step 1: Check Current VTP Status

Switch1> enable
Switch1# show vtp status

Expected output:

VTP Operating Mode              : Server
VTP Domain Name                 :

By default, the domain name is NULL, meaning no domain has been configured.

Repeat the same command on Switch2 and Switch3.

They will also show VTP Domain Name: NULL.

Step 2: Set the Domain Name on Switch1

Switch1# configure terminal
Switch1(config)# vtp domain ccnalab

Output:

Changing VTP domain from NULL to ccnalab

Important Notes:

The VTP domain name is case-sensitive — ccnalab, ccnaLab, and CCNALAB are different.
Once set, a domain name cannot be erased (only replaced).
All switches in the same domain must use identical names.

Step 3: Verify VTP Domain Synchronization

After setting vtp domain ccnalab on Switch1, check all switches again:

Switch2# show vtp status
Switch3# show vtp status

Output:

VTP Domain Name : ccnalab

Even though you only configured Switch1, the other switches automatically joined the same domain because they received VTP advertisements from Switch1.

Task 2: Configure VTP Modes

Goal: Assign each switch its correct mode — Server, Transparent, or Client.

Step 1: Confirm Current Mode

Switch1# show vtp status

Output:

VTP Operating Mode : Server

All switches default to Server mode initially.

Step 2: Configure Switch2 as Transparent

Switch2# configure terminal
Switch2(config)# vtp mode transparent

Output:

Setting device to VTP TRANSPARENT mode.

Verification:

Switch2# show vtp status
VTP Operating Mode : Transparent

Behavior: Transparent mode switches do not participate in VTP synchronization. They forward advertisements but do not apply them.

Step 3: Configure Switch3 as Client

Switch3# configure terminal
Switch3(config)# vtp mode client

Output:

Setting device to VTP CLIENT mode.

Verification:

Switch3# show vtp status
VTP Operating Mode : Client

Behavior: Client mode switches cannot create or delete VLANs. They depend entirely on updates from a VTP server.

Task 3: Verify VTP Operation

Goal: Test how VLAN creation behaves across different modes.

Step 1: Display Existing VLANs

Switch1# show vlan brief
Switch2# show vlan brief
Switch3# show vlan brief

Default VLANs: 1, 1002, 1003, 1004, 1005

Step 2: Create VLAN 10 on Switch1 (Server)

Switch1# configure terminal
Switch1(config)# vlan 10
Switch1(config-vlan)# name SALES
Switch1(config-vlan)# exit

Verify:

Switch1# show vlan brief

VLAN 10 appears as active.

Because Switch1 is a VTP server, the new VLAN automatically propagates to Switch3 (Client) but not to Switch2 (Transparent).

Check:

Switch2# show vlan brief  → VLAN 10 missing
Switch3# show vlan brief  → VLAN 10 present

Result: VLAN 10 replicated only to Switch3.

Step 3: Create VLAN 20 on Switch2 (Transparent)

Switch2# configure terminal
Switch2(config)# vlan 20
Switch1(config-vlan)# name HR
Switch1(config-vlan)# exit

Verification:

Switch2# show vlan brie

VLAN 20 appears locally, but does not propagate to Switch1 or Switch3.

Result: VLAN 20 is local-only to Switch2.

Step 4: Create VLAN 30 on Switch3 (Client)

Switch3(config)# vlan 30

Error:

VTP VLAN configuration not allowed when device is in CLIENT mode.

You cannot create VLANs in client mode.

Step 5: Create VLAN 30 on Switch1 (Server)

Switch1# configure terminal
Switch1(config)# vlan 30
Switch1(config-vlan)# name IT
Switch1(config-vlan)# exit

Verification:

Switch1# show vlan brief
Switch3# show vlan brief

VLAN 30 appears on both Switch1 and Switch3.

Switch2 forwards the VTP advertisement but does not apply it.

Final VLAN list:

Switch1 (Server): VLANs 1, 10, 30
Switch2 (Transparent): VLANs 1, 20
Switch3 (Client): VLANs 1, 10, 30

How VTP Synchronization Works: Conceptual Analogy

Picture three coworkers sharing files:

The Server keeps the master folder and updates everyone.
The Client automatically syncs its files from the server.
The Transparent coworker doesn’t join the shared folder but passes updates along to others.

Whenever you create a new VLAN on a server, VTP packages that information into advertisements and sends it over trunk links to all connected switches in the same domain.

These VTP advertisements contain:

VTP version (1, 2, or 3)
Domain name
Configuration revision number
List of VLANs

The configuration revision number increases whenever the VLAN database changes.

Clients use this number to determine if the update is newer and should replace their VLAN list.

Common Troubleshooting Cisco CLI Commands

Command	Purpose	Typical Use Case
`show vtp status`	Displays current VTP mode, domain, version, and revision number	Verify domain consistency and mode
`show vlan brief`	Lists all active VLANs	Check whether VLANs have propagated correctly
`show interfaces trunk`	Displays trunk link status	Confirm that trunking is active between switches
`vtp mode ?`	Shows available VTP modes	Check supported configurations
`vtp domain <name>`	Defines VTP domain	Ensure all switches share the same domain
`vtp password <string>`	(Optional) Adds VTP authentication	Prevents unauthorized VLAN updates

Key Takeaways

VTP automates VLAN distribution, reducing administrative workload.
All switches in a domain must share the same domain name and trunk links.
Server Mode: Can create, delete, and propagate VLANs.
Client Mode: Receives and applies VLANs but cannot modify them.
Transparent Mode: Creates local VLANs and forwards advertisements but ignores them.
VTP domain names are case-sensitive and cannot be removed once set.
VLANs only propagate over trunk links.

Quick Reference: VTP Troubleshooting Commands

# Display VTP status
Switch# show vtp status

# Display VLANs
Switch# show vlan brief

# Verify trunk links
Switch# show interfaces trunk

# Configure VTP domain
Switch(config)# vtp domain [domain]

# Change VTP mode
Switch(config)# vtp mode {server | client | transparent}

# Create VLAN
Switch(config)# vlan 10
Switch(config-vlan)# name [NAME]

Summary

VTP is a powerful Cisco feature that keeps VLAN configurations consistent across the network. When implemented properly, it can save hours of manual configuration. However, it must be handled carefully: one misconfigured switch with a higher revision number can overwrite VLAN databases across the domain.

Always remember to:

Verify VTP domain name and mode before adding a new switch.
Use show vtp status frequently.
Keep backups of VLAN databases before large-scale updates.

By understanding and mastering VTP, you gain a deeper control of Layer 2 network automation and scalability — a fundamental skill for every Cisco-certified network engineer.

Questions, comments, or just wanna drop a “hey”?
Go ahead — Just shoot an email to: fromzerotoccna@gmail.com

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