Things to know about VTP

Some notes about VTP (VLAN Trunking Protocol):

  • Cisco switches running Cisco IOS store VTP and VLAN information in a separate database stored in Flash, in file called vlan.dat.
  • Cisco switches running CatOS store VTP and VLAN information in the main switch configuration file, stored in NVRAM.
  • VTP information is only transmitted over trunk ports.
  • A VTP client does not need a VTP domain name to be configured to learn VLANs. If the domain name is left blank it will configure itself with the domain name learned from the first advertisement from the VTP server.
  • A VTP advertisement contains the VLANs configured in the domain that are allowed on the trunk, the VTP domain name, and the VTP configuration revision number.
  • If the revision number received in a VTP advertisement is greater than the current stored revision number, the switch will accept the new configuration and overwrite its existing vlan.dat file with the newly received VLAN configuration.
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