My VLANs are all gone?! "VTP Chaos" Packet Tracer Demo

This file was inspired by the example presented in APJ Instructor Forum on July 15, 2010.

Why a "vlan.dat" file for an IOS switch?

It looks to me the "vlan.dat" design will stay a long life on IOS switches.

How to remove VTP domain string: 2 reloads

To restore a IOS switch to a "whole new" state, it is necessary to clear even the "VTP domain" string to null. I thought at first just remove "vlan.dat" followed by a reload would do it, but now I found that I was NOT quite correct!

VTP Password can be shown!

I did not notice that we can use "show" commands to display the VTP (VLAN Trunking Protocol) password!

I was reminded by my student these days. We can see this document "Configuring VTP Global Parameters" for a sample.

Switch#show vtp password
VTP Password:WATER
Switch#

I should have known this in CCNA courses. How careless I am!

VTP Explained in Animation, on Cisco.com

I came across this Flash animation explaining VLAN Trunking Protocol (VTP), right on Cisco.com.

It is very clear and fully explaining many details about VTP. I believe it would help you to understand VTP even further!

http://www.cisco.com/warp/public/473/vtp_flash/

Enjoy it!

Enable VTP to distribute VLAN information, and provide two Virtual LAN (VLAN), using 3 connected switches (CNA-03-004)

CCNA Exploration 4.0, Semester 3, "Enable VTP to distribute VLAN information, and provide two Virtual LAN (VLAN), using 3 connected switches" Packet Tracer 5.0 practice file (CNA-03-004).

• CNA-03-004.pkt, (Backup Link)
• CNA-03-004-sol.pkt, (Backup Link)

The diagram is in fact the same as the previous example. You must have noticed that it is really bothering to add VLANs on switches one after one. In this case, we are going to make use of a special automatic method by IOS itself: the VTP protocol.

VTP stands for VLAN Trunking Protocol. It is a proprietary protocols among Cisco switches to distribute VLAN information.

Although it is not difficult for you to "peep" at "CoreSwitch"'s configuration in this Packet Tracer file, I wish you do not try it. What I want you to feel is to enable VTP only and then observe "Switch1" and "Switch2" getting VLAN information automatically!

In this case, "Switch1" and "Switch2" can play the VTP role as "Client". That is, it listens VLAN information advertised from the VTP "Server" role switches.

Client Configs:

Switch1(config)#vtp mode client
Switch1(config)#vtp domain ccna
Switch1(config)#

Server Configs:

CoreSwitch(config)#vtp mode server
CoreSwitch(config)#vtp domain ccna
CoreSwitch(config)#

Just like the VLAN information, we cannot see them in the running configuration. We can issue "show vtp status" command to check VTP status.

Switch1:

Switch1#show vtp status
VTP Version                     : 2
Configuration Revision          : 4
Maximum VLANs supported locally : 255
Number of existing VLANs        : 7
VTP Operating Mode              : Client
VTP Domain Name                 : ccna
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x9E 0x49 0xD8 0xC7 0xED 0x7C 0xB2 0x01 
Configuration last modified by 20.1.1.101 at 3-1-93 00:01:58
Switch1#

CoreSwitch:

CoreSwitch#show vtp status
VTP Version                     : 2
Configuration Revision          : 4
Maximum VLANs supported locally : 255
Number of existing VLANs        : 7
VTP Operating Mode              : Server
VTP Domain Name                 : ccna
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x9E 0x49 0xD8 0xC7 0xED 0x7C 0xB2 0x01 
Configuration last modified by 20.1.1.101 at 3-1-93 00:01:58
Local updater ID is 20.1.1.101 on interface Vl1 (lowest numbered VLAN interface found)
CoreSwitch#

Tips to clear Cisco VTP revision number

VLAN revision number is a crucial variable of Cisco's VTP (VLAN Trunking Protocol) . It mus be cleared to zero to be safely deployed. However, there is no specific command to do this.

To clear VTP revision number, the fastest way is to switch VTP mode to "Transparent Mode", and then switch back.

Another way to do the same thing is to change the domain string, and then back. But we would have to touch the domain string: it is where typo errors are easily made!