An operational mode is the mode a switch port is currently using: access or trunk. It differs from administrative mode, which is the mode configured with switchport mode. Manual access or trunk configuration makes both modes identical; dynamic modes use DTP to determine the result. section 13.1 section 13.3
DTP negotiation produces these common outcomes:
- Two dynamic auto ports remain access ports because neither actively tries to form a trunk. section 13.1.1
- A dynamic desirable port actively tries to form a trunk and can produce a trunk with dynamic auto, dynamic desirable, or trunk. section 13.1.1
- Use show interfaces interface-name switchport to compare administrative and operational modes. section 13.1.1
- For security, manually configure each port’s mode and disable DTP with switchport nonegotiate. section 13.3
Reading a negotiated port
If SW1 G0/0 uses administrative mode dynamic desirable while its neighbor uses dynamic auto, the operational mode becomes trunk. With both ports in dynamic auto, the operational mode remains static access. section 13.1.1
SW1# show interfaces g0/0 switchport Name: Gig0/0 Switchport: Enabled Administrative Mode: dynamic auto #1 Operational Mode: static access #2 . . . #1 G0/0’s configured mode is dynamic auto (default). #2 G0/0 functions as an access port.
Use the annotated switchport output to distinguish a configured dynamic auto port from its resulting operational access mode. section 13.1.1
