Chapter 12. Implementing Layer 2 Technologies

Implementing VLAN and VLAN Trunking Protocol


Dynamic Trunking Protocol (DTP) is a Cisco proprietary protocol that negotiates the trunking status of a switchport. Connected switches exchange DTP messages that indicate their desirability to create a trunk. The DTP port state dictates its capability to create a trunk. Following are the possible states:

auto: Enables the switch to create a trunk if initiated from the other switch. A switch programmed with auto cannot initiate a trunk but can form a trunk if the other side initiates. The trunk is formed with desirable and on.

desirable: Actively tries to create a trunk link with the peer. The trunk is formed with auto, desirable, and on.

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