VTP – VLAN Trunking Protocol

We are discussing a very interesting topic of switching i.e. VTP (VLAN Trunking Protocol). Through this blog, you can understand VTP and the role of VTP in switching. In this blog, we have discussed all things about VTP and its work function.

VTP- VLAN Trunking Protocol:

  • It is a Cisco proprietary protocol.
  • It works as layer 2.
  • The function of VTP (VLAN Trunking Protocol) is used to transfer VLAN information from one switch to another switch.
  • It is a centralized VLAN management.
  • It is used multicast MAC address 0100.0CCC.CCCC for VTP updates (CDP, VTP, UDLD).

VTP (VLAN Trunking Protocol) has three modes:

VTP VLAN Trunking Protocol

1. Server Mode

  1. Server Mode
  2. Client Mode
  3. Transparent Mode
vlan trunking protocol
  • In this mode, we can add, remove and edit VLAN.
  • It is the default mode of VTP on most of the series of switches.
  • It saves VLAN information in the vlan.dat file in flash memory.
  • In this mode, VTP can generate a VTP update.
  • It works as a relay agent.
  • Server mode supports only a normal range of VLAN.

2. Client Mode

  • In this mode, we can’t add, remove and edit VLAN.
  • It also stores information in its vlan.dat file.
  • It supports only a normal range of VLAN.
  • Client mode also works as a relay agent.
  • It can receive VLAN from another switch.

3. Transparent Mode

  • In this mode, we can add, remove or edit VLAN.
  • It is the default mode of VTP on some plate-form.
  • It doesn’t update its own VLAN database based on received VTP updates from its neighbor
  • It doesn’t forward its own VLAN information to any other switch and doesn’t generate VTP updates.
  • supports normal range VLAN as well as an extended range of VLAN.
  • It stores VLAN information in its vlan.dat file and also in the running configuration.
  • The transparent mode also works as a relay agent.

Criteria of VTP:

  • Trunking should be enabled between two switches.
  • The VTP domain name must be matched.
  • VTP password must match (optional).

Types of VTP Update:

  • Triggered update
  • Periodic update

C.R. Number (Configuration Revision):

  • It is in 32 bits.
  • This number is always represented in decimal.
  • By default C.R. number is 0.
  • It will always increment by one whenever any VLAN is added or removed in the VLAN database.

Types of VTP messages:

  • Summary advertisement
  • Subset advertisement
  • Advertisement request from the client

Summary Advertisement:

  • VTP server generates a summary advertisement message in every 300sec and every time when
    VLAN database change occurs.
  • It checks only C.R. numbers.

Contents of summary advertisement:

  • Domain name
  • Version
  • C.R. number
  • MD5 digest value (domain, password, CR number)
  • The total number of subset advertisement msg.

Subset Advertisement:

  • It contains actual information about VLAN changes.
  • It will generate when VLAN changes will occur.

Advertisement Request from Client:

  • The client switch might be reset and its VLAN database has cleared after that generate a client advertisement request message and the VTP server will respond with a summary advertisement and subset advertisement to bring it up to date.

VTP has three types of Versions:

  • version1
  • version2
  • version3

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