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DTP (Dynamic Trunking Protocol) | DTP Overview

DTP (Dynamic Trunking Protocol) is a Cisco Proprietary Protocol. DTP allows to switch devices select switchport mode (access or trunk) when connected to other switch.

DTP has some characteristic as the following :

  • is ON by default on Catalyst 2960 and 2950 switch series.
  • For dynamic-auto is on by default on catalyst 2960 and 2950.
  • We can disable with nonegotiate command and can be enable again by setting the interface to dynamic-auto.
  • when we do the setting to static trunk of static access it will be avoid to negotiation issues with the switchport mode trunk command or switchport mode access command.

The switchport mode command has some additional options.

  • Access :  the option will make to permanent access mode and negotiates to convert the neighboring link into an access link.
  • Dynamic Auto : the option will becomes trunk if the neighboring interface is set to trunk or dynamic desirable mode
  • Dynamic Desirable : this mode will actively seeks to become trunk by negotiating with other auto or desirable interfaces
  • Trunk : this mode will permanent set to trunk mode and will negotiates to convert the neighboring link into trunk link.

Here’s the Result of DTP Configuration option :

Dynamic Auto <-> Dynamic Auto  = ACCESS
Dynamic Auto <-> Dynamic Desirable = TRUNK
Dynamic Auto <-> Trunk = TRUNK
Dynamic Auto <-> Access = ACCESS
Dynamic Desirable <-> Dynamic Auto  = TRUNK
Dynamic Desirable <-> Dynamic Desirable = TRUNK
Dynamic Desirable <-> Trunk = TRUNK
Dynamic Desirable <-> Access = ACCESS
Trunk <-> Dynamic Auto  = TRUNK
Trunk <-> Dynamic Desirable = TRUNK
Trunk <-> Trunk = TRUNK
Trunk <-> Access = Limited Connectivity
Access <-> Dynamic Auto  = ACCESS
Access <-> Dynamic Desirable = ACCESS
Access <-> Trunk = Limited Connectivity
Access <-> Access = ACCESS





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