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DTP (Dynamic Trunking Protocol) — Key Facts and Modes
Which three statements about Dynamic Trunking Protocol (DTP) are true? (Choose three.)
Quick Answer
The answer is that DTP is a Cisco proprietary protocol used to automatically negotiate trunk links between switches. This is correct because DTP operates at Layer 2 and relies on the native VLAN (VLAN 1) to exchange its frames; if the native VLANs are mismatched on either side, the negotiation can fail. On the ENCOR 350-401 exam, DTP properties are tested to ensure you understand which switchport modes actively initiate trunking versus passively respond—a common trap is confusing “dynamic desirable” (which actively sends DTP frames) with “dynamic auto” (which only responds). Remember that DTP is never used on routed ports or Layer 3 interfaces, and it only applies to switch ports in access or trunk mode. A useful memory tip: “Desirable sends, Auto awaits”—the dynamic desirable mode actively seeks a trunk, while dynamic auto waits for an invitation.
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
✓
DTP is a Cisco proprietary protocol.
Correct: A is true because DTP is Cisco proprietary and not supported on non-Cisco switches. B is true because DTP uses VLAN 1 (the native VLAN) for its frames; if the native VLAN is mismatched, DTP may fail. C is true because the 'switchport mode dynamic desirable' interface configuration command actively sends DTP frames to negotiate trunking. D is incorrect because DTP operates at Layer 2, not Layer 3. E is incorrect because DTP is not used on routed ports; it only applies to switch ports in access or trunk mode.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DTP is a Cisco proprietary protocol.
Why this is correct
Correct because DTP is only available on Cisco switches and is not standardized.
- ✓
DTP frames are sent on the native VLAN.
Why this is correct
Correct because DTP uses the native VLAN (typically VLAN 1) to exchange negotiation messages.
- ✓
The 'switchport mode dynamic desirable' setting causes the interface to actively attempt to form a trunk.
Why this is correct
Correct because dynamic desirable mode sends DTP frames to encourage the neighbor to become a trunk.
- ✗
DTP operates at Layer 3 of the OSI model.
Why it's wrong here
Incorrect because DTP is a Layer 2 protocol used for trunk negotiation.
- ✗
DTP is used to negotiate trunking on routed ports.
Why it's wrong here
Incorrect because DTP only applies to Layer 2 switch ports; routed ports do not participate in DTP.
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Same concept, more angles
3 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which two statements about DTP (Dynamic Trunking Protocol) are true? (Choose two.)
medium- ✓ A.DTP is a Cisco proprietary protocol.
- ✓ B.The default switchport mode on a Cisco Catalyst switch is dynamic desirable.
- C.DTP frames are sent continuously on a trunk port to maintain the trunk.
- D.The 'switchport nonegotiate' command enables DTP on an interface.
- E.DTP supports both 802.1Q and ISL trunking encapsulation.
Why A: DTP is a Cisco proprietary protocol used to negotiate trunking between switches. The default mode on Cisco switches is dynamic desirable, which will actively try to form a trunk. DTP frames are sent only over access ports when trunking is being negotiated, but not over trunk ports once the trunk is established. The 'switchport nonegotiate' command disables DTP, and trunk formation then relies on manual configuration.
Variation 2. Drag and drop each DTP mode on the left to its matching trunking behavior on the right.
medium- ✓ P1.dynamic desirable: Actively sends DTP frames to form trunk
- ✓ P2.dynamic auto: Passively waits for DTP frames to form trunk
- ✓ P3.trunk: Forces the port to become a trunk regardless of neighbor
- ✓ P4.access: Forces the port to be an access port, no trunking
- ✓ P5.non-negotiate: Disables DTP, trunking only if manually configured
Why P1: Dynamic desirable actively negotiates trunking; dynamic auto waits for a neighbor to initiate; trunk forces trunking; access forces access mode; non-negotiate disables DTP.
Variation 3. Drag and drop each DTP mode on the left to its matching trunking behavior on the right.
medium- ✓ P1.dynamic desirable: Actively sends DTP frames; forms trunk if neighbor is trunk, desirable, or auto
- ✓ P2.dynamic auto: Passively waits for DTP frames; forms trunk only if neighbor is trunk or desirable
- ✓ P3.trunk: Forces the interface to be a trunk regardless of DTP negotiation
- ✓ P4.access: Forces the interface to be an access port; never forms a trunk
- ✓ P5.none (nonnegotiate): Disables DTP; requires manual trunk configuration
Why P1: Dynamic desirable actively sends DTP frames and forms a trunk if the neighbor is trunk, dynamic desirable, or dynamic auto. Dynamic auto forms a trunk only if the neighbor is trunk or dynamic desirable. Trunk always forms a trunk. Access never forms a trunk. None disables DTP.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.