VLANs: VLAN Trunking Protocol (VTP)

VTP advertises VLAN configuration information among a number of VTP participating switches in a LAN.  VTP advertises VLAN ID, VLAN name, and VLAN type and state for each VLAN configured to all other switches on the network.  VTP does not advertise the specific ports participating in those VLANs, so configuration associating specific switch port interfaces to specific VLANs is still required.

VTP exists in three versions, VTPv1, VTPv2, and VTPv3….

VTP versions 1 and 2 are widely supported across Cat-Os and IOS based switching platforms.  VTPv3 is still at present relatively new, VTP support starts on IOS release 12.2(52)SE.

VTPv1 is the default VTP version supported and active on IOs based switches, its only capable of supporting the dissemination of normal range VLANs only.

VTPv2 has the following new enhancements:

  • Supports token Ring concentrator Relay function and Bridge Relay Function (TrCRF and TrBRF) type VLANs: These VLANs were used to segment Token Ring networks into multiple logical rings and interconnecting bridges.  There is no use for these types of VLANs in Ethernet based networks.
  • Supports unknown Type-Length-Value (TLV) records: VTP Messages can contain additional information elements stored as TLV records.  VTPv1 usually drops all unrecognized TLVs from received messages, VTPv2 keeps all TLVs in propogated messages even if they are not recognized.
  • Optimized VLAN database consistency checking: VTPv1 only performed checks when the VLAN database was modified.  In VTPv2 the consistency checks are skipped if the change was caused by a received VTP message.

VTPv3 has the following enhancements from VTPv2:

  • The server role has been modified: There are two server types in VTPv3 primary and secondary, A primary server is allowed to modify VTP domain contents and there can only be on primary server per VTP domain at any time.
  • VTPv3 password storage has been improved.  the VTP password can now be stored in an encrypted format that cannot be displayed back as plaintext.
  • VTPv3 is capable of distributing information about the full range of VLANs including Private VLANs.  It is no longer necessary to use transparent mode when using extended range VLANs and Private VLANs.  Pruning still only applies to normal range VLANs.
  • VTPv3 supports an off mode where it will drop all received VTP messages and not participate in VTP operations.  You can also shut down VTP on specific trunks.



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