DTP is a Cisco proprietary feature that allows Cisco switches to negotiate trunk dynamically.
DTP has Three modes:
•On
•Desirable
Normally when you configure the command that switch mode trunk it means that port is going to become trunk whether you may have connected to a end hosts .
DTP Has three mode , Auto only responds and dynamic initiates the trunk .DTP is a cisco proprietary.
When you configure the dynamic desirable , it starts sending the DTP messages on that port .
When you configure the dynamic auto , it does not initiate the request only respond if other end initiate the request then it will respond .
Auto is passive and desirable is Active.
When you configure the switch mode trunk , it also sends the DTP messages and if other end switch is desirable or auto it can become trunk .
If both side is AUTO it means that port cant become trunk because no one initiate the request .
But cisco recommends and suggests to make the port as desirable in both ends ,
There are lots of combinations which can become the trunk as long as someone is initiating the request.
How T configure the DTP
Switch(config-if)# switchport mode dynamic [desirable|auto]
How To Disable DTP
Switch(config-if)# switchport nonegotiate
Verification command
Switch# show interface trunk
Switch# show interface <interface> switchport
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