Cisco CCNA (200-301)Network AccessEasy
A technician connects two new Catalyst switches with a single copper link and wants an 802.1Q trunk to form automatically using only default Dynamic Trunking Protocol (DTP) behavior, with no manual 'switchport mode trunk' command on either side. Which pair of switchport modes, one on each end, will successfully negotiate a trunk?
- Adynamic desirable on one end and dynamic auto on the other
- Btrunk on one end and access on the other
- Caccess on one end and dynamic desirable on the other
- Ddynamic auto on both ends
Show answer & explanationAnswer & explanation
Correct answer: A. dynamic desirable on one end and dynamic auto on the other
DTP dynamic desirable actively asks the neighbor to trunk, and dynamic auto will passively agree, so the link becomes a trunk. Two dynamic auto ports never initiate negotiation, so no trunk forms; access mode always refuses to trunk.
Why the other options are wrong
- B. Static trunk with static access causes a mismatch, not a clean DTP-negotiated trunk.
- C. Access mode statically refuses trunking regardless of the other side.
- D. Both ports only listen and never initiate, so the link stays access.
DTP Default Negotiation
Dynamic Trunking Protocol lets adjacent switchports automatically negotiate trunk or access mode based on configured DTP states.
- dynamic desirable + dynamic desirable = trunk
- dynamic desirable + dynamic auto = trunk
- dynamic auto + dynamic auto = access (no trunk)
- access mode never trunks regardless of the peer
Memory trick: Desirable asks, Auto answers, two Autos stay silent forever.