Question 362 of 1,389
CCNA Switching and Network Access Practice Question
Which four of the following are characteristics of Dynamic Trunking Protocol (DTP) and VLAN Trunking Protocol (VTP) used in Cisco switching? (Choose four.)
⚠ Common exam trap
Cisco often tests the distinction between DTP modes (dynamic desirable vs. dynamic auto) and the fact that VTP can cause catastrophic VLAN propagation errors if revision numbers are not reset before adding a switch to a production network.
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 used to negotiate trunking between two switches.
The four correct statements are: (1) DTP is a Cisco proprietary protocol for negotiating trunk links; (2) VTP synchronizes VLAN information across switches in the same VTP domain; (3) 'switchport mode dynamic desirable' actively sends DTP frames to form a trunk; (4) VTP pruning reduces unnecessary broadcast traffic by limiting flooded traffic to only switches that need the VLAN. The two incorrect statements: VTP transparent mode forwards VTP advertisements but does **not** modify its VLAN database based on received updates—it only passes them through. DTP **cannot** form a trunk when both ends are configured with 'switchport nonegotiate' because that command disables DTP frame transmission entirely, preventing trunk negotiation.
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 used to negotiate trunking between two switches.
Why this is correct
This is correct because DTP (Dynamic Trunking Protocol) is indeed Cisco proprietary, enabling Cisco switches to automatically negotiate whether the link should operate as an access port or a trunk port. It exchanges DTP frames over the link to agree on trunking parameters such as encapsulation (ISL or 802.1Q). Without DTP, trunks must be configured manually or via other mechanisms.
- ✓
VTP allows synchronization of VLAN information across switches in the same VTP domain.
Why this is correct
VTP (VLAN Trunking Protocol) is a Cisco Layer 2 messaging protocol that maintains VLAN configuration consistency across a switched network. Switches in the same VTP domain exchange VTP advertisements over trunk links, allowing VLAN creations, deletions, and renames to propagate automatically. This synchronization reduces administrative overhead by ensuring VLAN databases match across all participating switches.
- ✓
A switch configured with 'switchport mode dynamic desirable' actively attempts to form a trunk using DTP.
Why this is correct
When a switchport is set to 'dynamic desirable,' it actively sends DTP frames to the neighbor to encourage trunking. This mode can form a trunk if the neighbor is in trunk, desirable, or dynamic auto mode, because both sides exchange DTP and agree to enter trunking. It is the most aggressive DTP mode that still allows the port to become an access port if the neighbor does not respond.
- ✓
VTP pruning helps reduce unnecessary broadcast traffic by limiting flooded traffic to only switches that need the VLAN.
Why this is correct
VTP pruning enhances bandwidth efficiency by restricting flooded traffic (broadcasts, multicasts, and unknown unicasts) for a VLAN to only those trunk links that lead to switches with active ports in that VLAN. Without pruning, flooded frames are sent over every trunk in the VTP domain, wasting bandwidth. VTP pruning is enabled globally or per-VLAN and relies on VTP advertisements to inform switches which VLANs are needed.
- ✗
VTP transparent mode stores and forwards VTP advertisements but also modifies the VLAN database based on received updates.
Why it's wrong here
This statement is incorrect because a switch in VTP transparent mode does not modify its VLAN database based on received VTP updates; it only forwards VTP advertisements to other switches. Transparent switches maintain their own local VLAN database, which can be modified independently, and any VLAN changes made locally are not propagated. Thus, the claim that it modifies the VLAN database based on received updates is false.
- ✗
DTP can form a trunk regardless of whether both ends are configured with 'switchport nonegotiate'.
Why it's wrong here
This is incorrect because the 'switchport nonegotiate' command disables DTP frame transmission on a port. If either end of a link has nonegotiate configured, DTP cannot negotiate trunking, and the link will not become a trunk; it must be manually configured as a trunk. Therefore, DTP cannot form a trunk regardless of nonegotiate settings—at least one side must actively send DTP frames for negotiation to occur.
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Last reviewed: Jun 11, 2026
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