Supporting Multiple VLANs on a Single Trunk
Identifying the modes for Dynamic Trunking Protocol

Trunk links should be configured statically whenever possible; however, Catalyst switch ports run Dynamic Trunking Protocol (DTP) that can automatically negotiate a trunk link. This Cisco proprietary protocol can determine an operational trunking mode and protocol on a switch port when connected to another device that is also capable of dynamic trunk negotiation.

A DTP mode can be configured to turn the protocol off or to instruct it to negotiate a trunk link only under certain conditions as described in the figure.

NOTE:

General best practice is to set trunking to on and nonegotiate when a trunk link is required. DTP should be turned off on links where trunking is not intended.