The article explained in this section is the Dynamic Trunking Protocol (DTP). The topic is defined and described in this section in detail. And also different types of trunking modes used in the Dynamic Trunking Protocol (DTP) are also explained in the following part.

Dynamic trunking protocol (DTP) is one of the proprietary protocol and is developed by Cisco. Between the Cisco switches the networking protocol is used to remove the trunks automatically that appear in the switches. Dynamically DTP can remove the trunks and can form a connection between the switches in the Cisco.

DTP (Dynamic trunking protocol) is also used for removing the encapsulation type like IEEE 802.1Q or the ISL (Inter Switched Link). In the second layer of the OSI Model, this DTP works.

Different switch port modes are used by the DTP (Dynamic trunking protocol), they are defined in the below part.

  • Switch port mode access (DTP mode OFF) – here this mode tries to become a permanent non-trunking mode by putting the switch interface without taking care of whether the neighbour one is trying or is a trunk port or not. So it is called DTP (Dynamic trunking protocol) mode OFF. And these are accessed in the second layer.
  • Switch port trunk (DTP mode ON) – the interface is put into trunk mode. It is called DTP (Dynamic trunking protocol) mode ON because of the reason that they will become an interface even if the neighbour is trunk port or not.
  • Switch port mode dynamic auto – default mode used is dynamic auto by old Cisco switches. The conversion of the trunk link of an interface is performed here. If neighbour mode is trunk or desirable mode then the interface will be trunk mode. The trunk will not be formed when both the switches are auto.
  • Switch port mode dynamic desirable – the newer Cisco contain default mode is this. Here the mode will actively convert to a trunk link. If neighbours are auto, desirable, or trunk the interface will convert to a trunk link.
  • Switch port no negotiate – This mode prevents from converting to DTP (Dynamic trunking protocol) frames. If the mode is access or trunk only then this interface can be used.  

Different combinations of switch port mode

  1. Both interfaces configured with dynamic desirable mode
  2. One interface configured with dynamic desirable and other with dynamic auto mode.
  3. Both interfaces configured with dynamic auto mode.
  4. Both interfaces configured with trunk mode.
  5. One configured with trunk mode and the other with dynamic desirable mode.
  6. One configured with trunk mode and the other with dynamic auto mode.