mediumMultiple Choice
350-401 Practice Question: The purpose of the Dynamic Trunking Protocol…
What is the purpose of the Dynamic Trunking Protocol (DTP) on Cisco switches?
⚠ Common exam trap
Watch out — candidates often confuse DTP with VTP (VLAN Trunking Protocol), which manages VLAN database propagation, or assume DTP provides security features like encryption, when in fact it only negotiates trunking and can be a security risk.
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
✓
To automatically negotiate trunking between two Cisco switches.
DTP (Dynamic Trunking Protocol) is a Cisco proprietary protocol used to automatically negotiate the operational mode (access or trunk) of a switch port between two Cisco switches. When both ends are configured with DTP modes like dynamic desirable or dynamic auto, the link can become a trunk without manual configuration, simplifying deployment in environments where trunking is needed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
To automatically negotiate trunking between two Cisco switches.
Why this is correct
Dynamic Trunking Protocol (DTP) is a Cisco proprietary Layer 2 protocol operating on point-to-point Ethernet links to automatically negotiate a common trunking mode (access, trunk, desirable, auto) and establish an 802.1Q trunk when both switches are DTP-capable. It sends DTP frames on the native VLAN to determine whether the neighboring port is willing to become a trunk, thereby eliminating the need for manual trunk configuration. However, DTP only negotiates the trunking state; it does not define which VLANs are allowed on the trunk.
- ✗
To dynamically assign VLANs to access ports.
Why it's wrong here
DTP has no mechanism to place devices into specific VLANs; that task is performed by static interface VLAN assignment or by dynamic server-based methods such as VMPS (VLAN Membership Policy Server) or 802.1X/RADIUS VLAN assignment based on authenticated identity. DTP only negotiates whether a link is an access or trunk link, and if it becomes an access link, the VLAN is set locally per interface. Thus, claiming DTP dynamically assigns VLANs to access ports conflates trunk negotiation with VLAN membership, which is a distinct control-plane function.
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To provide security by encrypting trunk traffic.
Why it's wrong here
DTP is a control-plane protocol that sends unencrypted negotiation frames, so it provides no confidentiality, integrity, or authenticity for trunk traffic; encryption on trunk links requires an independent mechanism such as MACsec (802.1AE) or an IPSec VPN. In fact, DTP can be a security liability because a malicious device can spoof DTP frames to negotiate a trunk and perform VLAN hopping, which is why best practice is to disable DTP with 'switchport nonegotiate' on ports that should not trunk.
- ✗
To prevent loops in the network.
Why it's wrong here
Loop prevention in a switched Ethernet network is a function of Spanning Tree Protocol (STP), including RSTP or MST, which blocks redundant paths to guarantee a loop-free logical topology. DTP is entirely unrelated to this process; it simply negotiates the mode of a point-to-point link. Enabling DTP cannot stop or detect forwarding loops, and misconfigured trunk negotiation could even alter the topology graph that STP must compute.
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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.