Cisco CCNA (200-301)Network AccessHard
A network administrator needs to ensure that when a new switch is connected to an existing trunk port on SW1, the new switch automatically negotiates a trunk link. The new switch is also a Cisco Catalyst switch. Which 'switchport mode' configuration should be applied to the existing trunk port on SW1 to achieve this automatic negotiation?
- Aswitchport mode dynamic auto
- Bswitchport mode access
- Cswitchport mode trunk
- Dswitchport mode dynamic desirable
Show answer & explanationAnswer & explanation
Correct answer: D. switchport mode dynamic desirable
'switchport mode dynamic desirable' actively attempts to form a trunk link. If the connected switch is also in 'desirable' or 'auto' mode, a trunk will form. 'trunk' mode forces a trunk, but doesn't negotiate, while 'auto' waits passively.
Why the other options are wrong
- A. This mode passively waits for the other end to initiate trunking. If the new switch is also 'auto', no trunk will form.
- B. This configures the port as an access port, which will not form a trunk.
- C. This forces the port into trunking mode but does not actively negotiate with DTP; it expects the other side to be a trunk or to negotiate.
DTP Dynamic Desirable
The 'switchport mode dynamic desirable' command configures a switch port to actively attempt to convert the link into an 802.1Q or ISL trunk link using DTP (Dynamic Trunking Protocol).
- Actively seeks to form a trunk.
- Forms a trunk with 'desirable', 'auto', or 'trunk' on the other side.
- Requires DTP to be enabled.
Memory trick: Dynamic Desirable Always Trunks, Auto Waits.