VLAN trunking protocol

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VLAN trunking protocol

VTP stands for VLAN Trunking Protocol and is a protocol for the configuration and administration of VLANs in Cisco networks.

functionality

VTP is based on a domain concept and knows three different switch modes:

  • client
  • server
  • transparent
  • off (see Cisco web link)

VLANs on a switch can only be added, changed or deleted manually in server and transparent mode . These changes to the local VLAN database are passed on to all devices in the VTP domain via the trunks using a special command. In the transparent mode, these VTP advertisements are forwarded to other switches. The switch itself does not respond to these advertisements. In client mode, the VLAN database of the switch cannot be changed manually; the switch learns the VLAN configuration exclusively via the advertisements. Otherwise a client switch behaves identically to a server switch (among other things, it also distributes its VLAN database in the domain).

Each VTP database contains a configuration revision number . This number increases with every change. If a switch receives a VTP advertisement with a higher revision number, it takes over the received VLAN configuration, otherwise the advertisement is ignored. This applies to server and client switches, which can mean that a client switch accidentally moved into a domain with a suitable domain ID and high revision number can overwrite the VLAN databases of the entire domain.

When using VTP version 1 and 2, only VLANs from 1 to 1005 can be used. VTP version 3 supports extended VLAN (1006 to 4096). Advertisements are sent by a VTP server every five minutes and after changing the VLAN configuration on the server.

From the software versions

  • IOS 12.2 (33) SXI (Catalyst 65xx)
  • IOS 12.2 (33r) SRC3 (Catalyst 76xx) and
  • CATOS version 8.7 (1) (Catalyst 65xx)

VTP version 3 can be used. This means that extended VLANs can also be distributed. A change from version 2 to 3 is possible without failure. Clients that only master version 2 will continue to be supplied with replications in the range ≤ 1005.

literature

  • Steve McQuerry (Ed.): Interconnecting Cisco network devices . Pearson Education, Munich 2000, ISBN 3-8272-5799-9 , pp. 229 ff . ( limited preview in Google Book search).

Web links