Configuring a Trunk Link
Ports can become trunk ports either by static configuration or dynamic negotiation
using Dynamic Trunking Protocol (DTP). A switch port can be in one
of five DTP modes:
■ Access—The port is a user port in a single VLAN.
■ Trunk—The port negotiates trunking with the port on the other end of
the link.
■ Non-negotiate—The port is a trunk and does not do DTP negotiation
with the other side of the link.
■ Dynamic Desirable—Actively negotiates trunking with the other side
of the link. It becomes a trunk if the port on the other switch is set to
trunk, dynamic desirable, or dynamic auto mode.
■ Dynamic Auto—Passively waits to be contacted by the other switch. It
becomes a trunk if the other end is set to trunk or dynamic desirable
mode.
Configure a port for trunking at the interface configuration mode:
(config-if)#switchport mode {dynamic {auto | desirable} | trunk}
If dynamic mode is used, DTP negotiates the trunking state and encapsulation.
If trunk mode is used, you must specify encapsulation:
(config-if)#switchport trunk encapsulation {isl | dot1q | negotiate}