VLAN Trunk Protocol (VTP)

 

VLAN Trunk Protocol (VTP)

VLAN Trunk Protocol (VTP) reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributed through all switches in the domain. This reduces the need to configure the same VLAN everywhere.

VTP is a Cisco-proprietary protocol that is available on most of the Cisco Catalyst series products.

VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs within a VTP domain. A VTP domain (also called a VLAN management domain) is made up of one or more network devices that share the same VTP domain name and that are interconnected with trunks. VTP minimizes misconfigurations and configuration inconsistencies that can result in several problems, such as duplicate VLAN names, incorrect VLAN-type specifications, and security violations.

Before you create VLANs, you must decide whether to use VTP in your network. With VTP, you can make configuration changes centrally on one or more network devices and have those changes automatically communicated to all the other network devices in the network.

 

Requirement of VTP-

1.      Trunking must be enabled between every switch.

2.      The VTP domain name must match every switch.

3.      The VTP password must match.

 

Types of VTP mode-

1.      Server Mode- In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters (such as VTP version and VTP pruning) for the entire VTP domain. VTP servers advertise their VLAN configuration to other network devices in the same VTP domain and synchronize their VLAN configuration with other network devices based on advertisements received over trunk links. VTP server is the default mode. We can create only a normal range of VLANs and it stores VLAN database information in flash memory vlan.dat file

2.      Client Mode- VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

3.      Transparent Mode- VTP transparent network devices do not participate in VTP. A VTP transparent network device does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, a transparent network device will forward receive VTP advertisements from its trunking LAN ports. In VTP version 3, a transparent network device is specific to an instance. We can create an extended range of VLANs it stores VLAN database information in flash memory vlan.dat file as well as running config.

 

4.      Off Mode- In VTP off mode, a network device functions in the same manner as a VTP transparent device except that it does not forward VTP advertisements.

 

Configuration Revision Number

The configuration revision number is a 32-bit number that indicates the level of revision for a VTP packet. Each VTP device tracks the VTP configuration revision number that is assigned to it. Most of the VTP packets contain the VTP configuration revision number of the sender.

This information is used to determine whether the received information is more recent than the current version. Each time that you make a VLAN change in a VTP device, the configuration revision is incremented by one. To reset the configuration revision of a switch, change the VTP domain name, and then change the name back to the original name. Updater ID – lower sVI id will become updater id

 

VTP Messages-

1.      Summary Advertisement- Periodically after every 300 seconds, triggered whenever any VLAN database change will occur. Contents of Summary Advertisement such as VTP Domain, CR Number, MD5 digest value(domain name, password, and CR no.), Version., Total no. of summary subset messages.

2.      Subset Advertisement- Triggered when any changes will occur.

3.      Subset Request- In the response to the subset request, it contains actual VLAN information 

 

VTP Version-

VTP Version 1

1.      This is the default version on IOS switches

2.      Supports the normal VLAN range (1-1005)

3.      Supports VLAN pruning for VLANs 2-1001

4.      Operates in Server, Client, or Transparent modes

5.      Supports both plain text or MD5 password

6.      Drops unknown TLVs

VTP Version 2

1.      Supports normal VLAN range (1-1005)

2.      Extended VLANs can be used in Transparent Mode only

3.      Added support for Token Ring Concentrator Relay Function and Bridge Relay Function

4.      Added support for unknown TLV records

5.      Optimized VLAN database consistency checking

6.      GVRP – Generic VLAN Registration Protocol (Non-Cisco Devices have this protocol and VTP Ver 2 supports this

VTP Version 3

1.      It supports extended VLANs

2.      Advertises Private VLAN configuration

3.      Advertises other databases (including Multiple STP)

4.      Different modes can be set for different features.

5.      Password can be set to hidden or secret.

6.      It will create private VLAN in server mode, can Encrypt passwords,

7.      It supports extended VLAN,

8.      Propagate MSTP configuration.

9.      Off mode – enable disable VTP per port.

10.  Fixes configuration revision overwrite problem that exists in v1/v2 by introducing the primary and secondary server