Question 668 of 1,389
CCNA Switching and Network Access Practice Question
Which command places a switch interface into trunking mode directly instead of relying on negotiation?
⚠ Common exam trap
Be careful not to confuse commands that involve negotiation or specify encapsulation with those that directly set the mode.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
switchport mode trunk
The direct command is `switchport mode trunk`. In plain language, this tells the switch to behave as a trunk port rather than waiting to negotiate that role through DTP. That makes the administrative intent clear and avoids ambiguity. In many production environments, explicit configuration is preferred because it is easier to understand and troubleshoot than relying on negotiation behavior. This is a core CCNA switching idea because trunks and access ports serve very different purposes. The wrong answers either describe negotiation states or commands that relate to other aspects of VLAN behavior. The best answer is the one that directly forces the interface into trunk mode instead of merely suggesting or passively waiting for trunking.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
switchport mode trunk
Why this is correct
The switchport mode trunk command explicitly configures the interface as an 802.1Q trunk, forcing it to carry traffic for multiple VLANs over the link. This direct configuration overrides any dynamic trunking protocol (DTP) negotiation, ensuring the port advertises itself as a trunk regardless of the neighbor's default state. It is the only command among these that definitively places the interface into trunking mode without relying on remote device behavior.
- ✗
switchport access vlan 10
Why it's wrong here
The switchport access vlan 10 command assigns the interface to VLAN 10 as a static access port, which means the port carries traffic for only that single VLAN using untagged frames. This command implicitly sets the interface into access mode, not trunking mode, so it cannot carry multiple VLANs simultaneously. Since trunking requires tagging and support for multiple VLANs, applying this command prevents the port from functioning as a trunk unless a subsequent mode command overrides it.
When this WOULD be correct
In a different question, if asked about configuring an access port for a specific VLAN, 'switchport access vlan 10' would be the correct answer. For example, a question might ask how to set an interface to carry traffic for VLAN 10 only.
- ✗
switchport mode dynamic auto
Why it's wrong here
The switchport mode dynamic auto command instructs the interface to form a trunk only if the neighboring interface explicitly requests trunking via DTP, typically by being in dynamic desirable or trunk mode. This does not directly force the interface into trunking mode; instead, it leaves the final state dependent on the peer's configuration. If the neighbor is set to dynamic auto or access, the link will remain an access port, so this command cannot guarantee trunk operation.
When this WOULD be correct
In a scenario where the question asks for a command that enables dynamic trunking negotiation, 'switchport mode dynamic auto' would be correct. For example, if the question specified the need for a switch to automatically negotiate trunking with a connected switch, this command would be appropriate.
- ✗
spanning-tree portfast
Why it's wrong here
The spanning-tree portfast command is a Spanning Tree Protocol feature that transitions an access port directly to the forwarding state, bypassing the listening and learning phases. It is designed for edge ports connected to end devices, not for configuring VLAN trunking behavior. Because it does not alter the switchport mode (access vs. trunk), it has no effect on whether an interface participates in trunking multiple VLANs.
When this WOULD be correct
If the exam question asked about configuring an interface to quickly transition to forwarding state for end devices, 'spanning-tree portfast' would be the correct answer. This scenario would focus on optimizing STP for access ports rather than trunking.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓switchport mode trunkCorrect answer▾
Why this is correct
The switchport mode trunk command explicitly configures the interface as an 802.1Q trunk, forcing it to carry traffic for multiple VLANs over the link. This direct configuration overrides any dynamic trunking protocol (DTP) negotiation, ensuring the port advertises itself as a trunk regardless of the neighbor's default state. It is the only command among these that definitively places the interface into trunking mode without relying on remote device behavior.
✗switchport access vlan 10Wrong answer — click to see why▾
Why this is wrong here
The command 'switchport access vlan 10' assigns the interface to a specific access VLAN, placing it in access mode, not trunk mode. Trunk mode is required to carry multiple VLANs, and this command does not enable trunking.
★ When this WOULD be the correct answer
In a different question, if asked about configuring an access port for a specific VLAN, 'switchport access vlan 10' would be the correct answer. For example, a question might ask how to set an interface to carry traffic for VLAN 10 only.
Why candidates choose this
Students might confuse VLAN assignment with trunking, thinking that specifying a VLAN somehow enables trunking. However, trunking is about tagging frames from multiple VLANs, not just assigning a single VLAN.
✗switchport mode dynamic autoWrong answer — click to see why▾
Why this is wrong here
The command 'switchport mode dynamic auto' places the interface in a mode that waits for the neighboring switch to initiate trunking via DTP. It does not directly force trunking; the interface will only become a trunk if the neighbor is set to 'dynamic desirable' or 'trunk'.
★ When this WOULD be the correct answer
In a scenario where the question asks for a command that enables dynamic trunking negotiation, 'switchport mode dynamic auto' would be correct. For example, if the question specified the need for a switch to automatically negotiate trunking with a connected switch, this command would be appropriate.
Why candidates choose this
Test-takers may think 'dynamic auto' automatically creates a trunk, but it actually relies on negotiation and does not guarantee trunking. It is often confused with 'dynamic desirable', which actively attempts to form a trunk.
✗spanning-tree portfastWrong answer — click to see why▾
Why this is wrong here
The command 'spanning-tree portfast' is used to speed up the transition of an access port to the forwarding state, bypassing the listening and learning phases. It has no effect on trunking mode and is unrelated to VLAN trunk configuration.
★ When this WOULD be the correct answer
If the exam question asked about configuring an interface to quickly transition to forwarding state for end devices, 'spanning-tree portfast' would be the correct answer. This scenario would focus on optimizing STP for access ports rather than trunking.
Why candidates choose this
Students might associate 'portfast' with fast convergence or think it enables some form of trunking, but it is purely an STP optimization for edge ports and does not affect trunk mode.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Last reviewed: May 17, 2026
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