DTP (Dynamic Trunking Protocol)

• DTP is a Cisco proprietary protocol.
• DTP is used by cisco switches to find weather the other switch automatically wants to negotiate trunk or not.
• If both the switches agree to negotiate trunk, then automatically trunk is formed.
• DTP by default runs on all the ports of cisco switches.
• DTP messages are sent every 30 seconds.
• DTP modes:
  1. Dynamic auto
     • Dynamic auto mode prefers to remain access port, but if someone willing to asks dynamic auto mode to negotiate trunk, then it does negotiate trunk automatically.
  2. Dynamic Desirable
     • Dynamic desirable mode prefers to become trunk port.
     • So it sends DTP messages inside in which it willingly says that  “lets become trunk”
  3. On
     • On mode of DTP is achieved when you forcefully make a port trunk port.
     • If a port has been made trunk port forcefully then it does not care if the other end becomes trunk port or not, but make itself trunk port.
• Advantages of DTP:
  1. Administrative labour is reduced.
  2. Misconfiguration will also be reduced.
     • DA    –     DA      (not form trunk)
     • DA    –     DD      (forms trunk)
     • DD    –     DA      (forms trunk)
     • ON    –     DA      (forms trunk)
• DTP not only negotiate trunk, DTP negotiate trunk encapsulation also.
• Configuration – #switchport trunk encapsulation negotiate
• To disable DTP –  #switchport mode nonegotiate