How DTP work when it connect access or trunk of other end?

Hello Hassan,

Good Day.

Thank you for writing your question on "ASK NB" portal.

Kindly refer your solution below & write us back if any further concern.

===============================

The Dynamic Trunking Protocol (DTP) is used to negotiate forming a trunk between two Cisco devices. DTP causes increased traffic, and is enabled by default, but may be disable
So if the port is an access port but DTP is not disabled it will still be on depending on what is set on the other side of the link. Example like if  a PC is connected to switch port which is set to dynamic desirable the link will be an access link but the DTP will still be ON and trying to negotiate.

port set to dynamic Auto will operate as access port but they will be listening for any DTP negotiation from the other side hoping the other side will initialize it.

Ethernet trunk interfaces support different trunking modes. An interface can be set to trunking or non trunking, or to negotiate trunking with the neighbor interface. Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP), which operates on a point-to-point basis only, between network devices.
DTP is a Cisco proprietary protocol that is automatically enabled on Catalyst 2960 and Catalyst 3560 Series switches. Switches from other vendors do not support DTP. DTP manages trunk negotiation only if the port on the neighbor switch is configured in a trunk mode that supports DTP.

Negotiated Interface Modes 

Ethernet interfaces on Catalyst 2960 and Catalyst 3560 Series switches support different trunking modes with the help of DTP:

•    Switch port mode access: Puts the interface (access port) into permanent non trunking mode and negotiates to convert the link into a non trunk link. The interface becomes a non trunk interface, regardless of whether the neighboring interface is a trunk interface.

•    Switch port mode dynamic auto: Makes the interface able to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk or desirable mode. The default switch port mode for newer Cisco switch Ethernet interfaces is dynamic auto. Note that if two Cisco switches are left to the common default setting of auto, a trunk will never form.

•    Switch port mode dynamic desirable: Makes the interface actively attempt to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto mode. This is the default switch port mode on older switches, such as the Catalyst 2950 and 3550 Series switches.
•    Switch port mode trunk: Puts the interface into permanent trunking mode and negotiates to convert the neighboring link into a trunk link. The interface becomes a trunk interface even if the neighboring interface is not a trunk interface.

•    Switch port No negotiate: Prevents the interface from generating DTP frames. You can use this command only when the interface switch port mode is access or trunk. You must manually configure the neighboring interface as a trunk interface to establish a trunk link.

===========================================

Regards,

PS. Pandey