What is VTP (Vlan Trunking Protocol) and how it works | Network Educator

What is VTP (Vlan Trunking Protocol) and how it works

Cisco switches use its own proprietary VTP to exchange VLAN information between each other. VTP (VLAN Trunking Protocol) defines a Layer 2 messaging protocol that let the switches share VLAN configuration information so that the configuration of VLAN remains consistent throughout that network.

For Example, if we want to use VLAN 8 and name it as “Sales-VLAN”, we can configure that VLAN configuration in one switch, and VTP will distribute that information to the rest all the switches in the network.
VTP manages the additions, deletions, and modification such as name changes of VLANs across multiple switches which eventually minimize the time in doing the VLAN configuration, changes of misconfiguration becomes less such as duplicate VLAN names or incorrect VLAN setting.

Suppose if there are 20 switches in a network which are interconnected and we have to configure same VLANs in all the switches. If VTP has been configured then we don’t need to configure the VLANs in all the 20 switches, we have to configure the VLANs only in one switch (will be referred as VTP Server) and in rest of the switches VLANs would be learned dynamically.

Understanding the VTP process
Using VTP process, VLANs are being created in a switch which will be referred as VTP server. VLANs which are created or changed are distributed as a broadcast throughout the network.
VTP clients and servers exchanges the VTP messages and update their configuration based on those messages. So VTP allows switched network to expand to large size network by reducing the manual effort which is required for the configuration.

How VTP Works
VTP floods advertisements throughout the VTP domain every 5 minutes, or whenever there is a change in VLAN configuration. The VTP advertisement includes a configuration revision number, VLAN names and numbers, and information about which switches have ports assigned to each VLAN. By configuring the details on one (or more) VTP server and propagating the information through advertisements, all switches know the names and numbers of all VLANs

vtp

VTP operates in one of three modes

  1. Server mode
  2. Client mode
  3. Transparent mode

VTP Server

  • Can create, modify, and delete VLANs and other configuration for entire VTP domain.
  • Will propagated VLAN config to the VTP clients and servers in that same domain.
  • VLAN configurations is saved in NVRAM.

VTP Clients

  • Cannot create, change, or delete VLANs configuration.
  • No VLAN configuration is not stored.
  • No VLAN configuration is saved in NVRAM.

VTP Transparent

  • Can create, modify, and delete VLANs
  • Changes are not transmitted to other switches in the domain but they will effect on only that switch.
  • Ignore the VTP messages but forward VTP advertisements received from other switches.

Functional Difference between VTP Modes

Function

Server Mode

Client Mode

Transparent Mode

Can create, modify, or delete VLANs within switch

Yes

No

Yes

Forwards VTP advertisements to other switches connected via trunk

Yes

Yes

Yes

Processes received advertisements and synchronizes VLAN config

Yes

Yes

No

Originates VTP advertisements

Yes

No

No

Saves VLAN configuration in NVRAM

Yes

No

Yes

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