On a Cisco Catalyst 2960 switch, you want to configure a port as an 802.1Q trunk so that it can carry multiple VLANs between switches. Which command should you use on the interface to set the switchport into permanent trunk mode?

Introduction / Context:
Cisco Catalyst switches such as the 2960 are commonly used to create VLAN aware switched networks. To carry traffic for multiple VLANs across a single physical link between switches or between a switch and a router, you must configure that link as a trunk. On some models, encapsulation is fixed to 802.1Q, and you only need to set the switchport mode. This question asks which specific interface configuration command puts a port into permanent trunk mode on a 2960 switch.

Given Data / Assumptions:

• The device is a Cisco Catalyst 2960 switch.
• You are configuring an interface in interface configuration mode.
• The goal is to carry traffic for multiple VLANs over that port.
• The encapsulation type is not configurable on the 2960 because it uses 802.1Q only.

Concept / Approach:
On 2960 switches, the encapsulation for trunks is fixed to dot1q, so you do not use a trunk encapsulation command. Instead, you control whether a port operates as an access port or a trunk port using the switchport mode commands. The command switchport mode trunk forces the port into permanent trunk mode, meaning it sends and receives tagged frames for multiple VLANs. Other commands such as switchport mode access or dynamic desirable configure other behaviors through Dynamic Trunking Protocol, but the question is specifically about setting a trunk port directly.

Step-by-Step Solution:
1. Enter interface configuration mode on the switch for the desired port. 2. Recall that for a 2960 switch, trunk encapsulation is not configurable, so you do not need an encapsulation command. 3. Use the switchport mode command to choose between access, trunk, and dynamic modes. 4. To make the port always act as a trunk, enter the command switchport mode trunk. 5. After this, you can specify allowed VLANs if necessary, but the basic trunk function is established by this mode command.

Verification / Alternative check:
In Cisco documentation and lab examples, configuring a trunk on a 2960 switch always includes lines similar to interface FastEthernet0/24 followed by switchport mode trunk. The absence of a switchport trunk encapsulation command is normal on these models, confirming that mode selection is the key. Running the show interfaces trunk command afterward will list the port as a trunk, which verifies that the configuration is correct.

Why Other Options Are Wrong:
Option a: trunk on is not a valid Cisco IOS command for configuring trunks on 2960 switches. Option b: trunk all is not a valid interface mode command in IOS. Option c: switchport trunk on is not correct syntax; Cisco uses switchport mode trunk to set the mode. Option e: switchport trunk encapsulation dot1q is used on some platforms that support multiple encapsulation types, but 2960 switches use only dot1q and do not require or allow this command. Even on platforms where it exists, you still need switchport mode trunk to enable trunking.

Common Pitfalls:
A common mistake is to assume that encapsulation must always be set explicitly, even on platforms where it is fixed. On exams, options may include valid commands from other switch models to distract you. Another pitfall is confusing interface configuration mode commands with global configuration or EXEC mode syntax. Always pay attention to the prompt shown in example commands and remember that switchport configuration is done at the interface level. Practicing on real or simulated 2960 devices makes the correct syntax very familiar and reduces the chance of choosing invalid options.

Final Answer:
To put a port into permanent trunk mode on a 2960 switch, use switchport mode trunk in interface configuration mode.