VLAN Trunking Protocol

• VTP is a cisco proprietary protocol.
• VTP is used to share VLAN information automatically between cisco switches.

There are few things that are taken into consideration when configuring VTP.

• The switches need to belong to the same VTP domain if you want them to share VLAN information automatically.
• VTP updates can only be sent via trunk ports, they cannot be sent via access ports.
• VTP has authentication feature, so if authentication is enabled then the passwords must match on all the switches.
• If a switch belongs to VTP domain null (nothing), then such a switch cannot originate VTP messages.
• By default cisco switches are configured with VTP domain NULL.
• A switch can be kept in one of VTP modes.
  • VTP server switch
  • VTP client switch
  • VTP transparent switch
• These modes define how a switch will behave in VTP:
  • How the switch will send VTP messages.
  • And how the switch will receive VTP messages.
• VTP server switch is that switch we create, delete and modify VLANs.
• VTP server switches send updates with the help of which they provide VLAN information to other switches.
• VTP client switch receives information from VTP server switch, you cannot create, delete and modify VLANs on client switch.
• By default all the switches are in VTP server mode.
• BY default VTP is enabled on cisco switches.
• Configuration revision number value.
  • CR number starts from 0 on all the switches, be it server switch, client switch or transparent switch.
  • Whenever there is a change in the VLAN database, this value is incremented by 1.
  • CR number value always remains 0 on the transparent switch.
• Transparent switches do not process VTP updates themselves, but they do act as a VTP relay agents.
• VTP Transparent switches maintain its own local VLAN database that it does not shares with anyone.
• It does not originate VTP messages itself.