Administrative mode is a switch port’s configured mode, set with switchport mode. It determines whether the port operates manually as access or trunk, or negotiates through DTP. section 13.1 section 13.1.1
Cisco switch ports support four administrative modes:
- access: Forces access operation and does not send DTP messages. section 13.1 section 13.1.1
- trunk: Forces trunk operation and sends DTP messages. section 13.1 section 13.1.1
- dynamic auto: Uses DTP but does not actively request a trunk; two auto ports remain access ports. section 13.1.1
- dynamic desirable: Uses DTP and actively attempts to form a trunk with a compatible neighbor. section 13.1.1
Reading administrative and operational modes
With both ports in dynamic auto, the link operates as access. Changing SW1 G0/0 to dynamic desirable causes negotiation with SW2’s dynamic auto port, producing an operational trunk. Verify both values with show interfaces g0/0 switchport. section 13.1.1
DTP is Cisco-proprietary and considered a security vulnerability. Best practice is to configure each port manually and disable negotiation with switchport nonegotiate on. section 13.3 section 13.1
