Dynamic Trunking Protocol (DTP)

Dynamic Trunking Protocol (DTP) is the Cisco-proprietary protocol that actively attempts to negotiate a trunk link between two switches. Below is the switchport modes (or DTP modes) for easy reference:

ModeFunction
Dynamic AutoCreates the trunk based on the DTP request from the neighboring switch.
Dynamic DesirableCommunicates to the neighboring switch via DTP that the interface would like
to become a trunk if the neighboring switch interface is able to become a trunk.
TrunkAutomatically enables trunking regardless of the state of the neighboring switch
and regardless of any DTP requests sent from the neighboring switch.
AccessTrunking is not allowed on this port regardless of the state of the neighboring
switch interface and regardless of any DTP requests sent from the neighboring
switch.
NonegotiatePrevents the interface from generating DTP frames. This command can be
used only when the interface switchport mode is access or trunk. You must
manually configure the neighboring interface as a trunk interface to establish a
trunk link.


Below figure shows the combination of different modes 

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