Course contents

Chapter 5: LAN SwitchingLesson 10 of 11

Packet Tracer lab: VTP server, client and transparent

Three switches in Packet Tracer: configure VTP modes and a domain, watch VLANs propagate, and see why revision numbers matter.

Intermediate · 20 min read

Technical definition

Packet Tracer VTP lab builds three switches that share a VTP domain. One server creates VLANs, a client copies them, and a transparent switch keeps its own list while passing advertisements along.

What you will build

This walkthrough was written from Cisco IOS documentation and Packet Tracer behaviour as generally described. It has not been run in Packet Tracer here, so port names and prompts can differ slightly on your version.

Packet Tracer topology: VTP server, transparent and client in a line
Packet Tracer topology: VTP server, transparent and client in a lineSW1 is the VTP server, SW3 is the transparent switch in the middle, SW2 is the client. All links are trunks. The domain is ROUTELEARN, version 2.Gi0/1 trunkGi0/2 trunkSW1serverSW3transparentSW2client
Everything is trunked. SW3 is in the middle to show that a transparent switch forwards VTP advertisements but does not apply them.

Use three 2960 switches. Cable SW1 Gi0/1 to SW3 Gi0/1 and SW3 Gi0/2 to SW2 Gi0/1; the labels above show the intended ports. No PCs are needed, because the lab only checks the VLAN lists.

Step 1: trunks on every link

! SW1 interface GigabitEthernet0/1 switchport mode trunk ! SW3 interface range GigabitEthernet0/1 - 2 switchport mode trunk ! SW2 interface GigabitEthernet0/1 switchport mode trunk

VTP advertisements travel only across trunks. If your version rejects the command, add switchport trunk encapsulation dot1q first.

Step 2: VTP modes, domain and version

! SW1 vtp mode server vtp domain ROUTELEARN vtp version 2 vtp password RL-Lab1 ! SW2 vtp mode client vtp domain ROUTELEARN vtp password RL-Lab1 ! SW3 vtp mode transparent vtp domain ROUTELEARN vtp version 2

Domain names and passwords must match for switches to accept each other's advertisements. The version is learnt from the server by a client. A transparent switch needs the domain only to forward the frames.

Example output · based on Cisco documentation; exact format varies by platform and software version
SW1#show vtp status
VTP Version capable             : 1 to 3
VTP version running             : 2
VTP Domain Name                 : ROUTELEARN
VTP Operating Mode              : Server
Number of existing VLANs        : 5
Configuration Revision          : 0
Example output. Confirm the domain, the mode and the version. The Configuration Revision starts at 0 and rises by one every time VLANs change on the server.

Step 3: create VLANs on the server only

! SW1 vlan 10 name SALES vlan 20 name SUPPORT vlan 30 name GUEST

Three VLANs on the server. Each change bumps the revision number and triggers an advertisement.

Step 4: check who received them

What each switch should show
What each switch should showSwitch; Mode; show vlan brief should list; Why. SW1: Server VLANs 10, 20, 30 Created here SW2: Client VLANs 10, 20, 30 Learnt from the server through SW3 SW3: Transparent No new VLANs Keeps its own list; forwards the advertisementSwitchModeshow vlan brief shouldlistWhySW1ServerVLANs 10, 20, 30Created hereSW2ClientVLANs 10, 20, 30Learnt from the serverthrough SW3SW3TransparentNo new VLANsKeeps its own list;forwards theadvertisement

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Allow a few seconds for the advertisement. In Packet Tracer, 'show vtp status' on SW2 should show the same revision as SW1.

Now create vlan 99 on SW3. It exists on SW3 only: a transparent switch's changes stay local and are not advertised.

Step 5: see why the revision number matters

  1. Note SW1's revision (for example 3).
  2. Imagine a spare switch in the same domain with a revision of 20 and an empty VLAN list. Plugged in over a trunk, it would win, and SW1 and SW2 would delete VLANs 10, 20 and 30.
  3. That is why a switch should be reset before it joins a domain, and why many networks use transparent mode or VTP version 3 with a primary server instead.

Do not try this on a lab you want to keep; reproduce it only on a throwaway copy of the file.

Common Packet Tracer problems

  • The client shows no VLANs: check the trunk, the domain name (case matters) and the password on both ends.
  • VLANs created on a client are refused: a client cannot create them.
  • The revision does not move: confirm the server really changed the VLAN list.

Test yourself

Predict · scenario 1

Which VTP mode can create, change and delete VLANs and advertise them?

Predict · scenario 2

What does a transparent switch do with received VTP advertisements?

Predict · scenario 3

What must match for two switches to share VLANs through VTP?

Predict · scenario 4

A switch with a higher revision number and an empty VLAN list joins a domain. What can happen?

Predict · scenario 5

Where do VTP advertisements travel?

FAQ

Why does the transparent switch not receive the VLANs?
A transparent switch keeps its own VLAN list and does not apply advertisements; it only forwards them (in version 2) so switches behind it can still receive them.
Can a VTP client create a VLAN?
No. A client takes its VLAN list from the server. Create or change VLANs only on a server, or on a transparent switch for local use.
What is the revision number danger?
A switch with a higher configuration revision number overwrites the VLANs of the whole domain when it joins. Reset the revision before adding an old switch, for example by changing the domain name and back, or setting transparent mode and then back.