200-901 Network Fundamentals Practice Question
A network engineer is analyzing traffic and needs to identify which applications use UDP. Which three applications commonly use UDP as their transport protocol? (Choose three.)
⚠ Common exam trap
Cisco often tests the distinction between control plane protocols (like DHCP, DNS, NTP) that use UDP for efficiency versus management or data transfer protocols (like SSH, SMTP) that require TCP's reliability, leading candidates to mistakenly associate all 'important' traffic with TCP.
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
✓
DHCP
DHCP (A) is correct because it uses UDP ports 67 (server) and 68 (client) for its broadcast-based DORA process, since UDP's connectionless nature suits the initial address assignment before a client has an IP. DNS (D) is correct because standard DNS queries and responses use UDP port 53 for lightweight, fast lookups, falling back to TCP only for large responses or zone transfers. NTP (E) is correct because it uses UDP port 123 for time synchronization, where occasional packet loss is acceptable and the low overhead of UDP is preferred. SSH (B) is not correct because it relies on TCP port 22 for reliable, ordered, connection-oriented sessions. SMTP (C) is not correct because it uses TCP port 25 (and 587/465) to guarantee reliable delivery of mail messages.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DHCP
Why this is correct
DHCP relies on UDP because clients broadcast discovery packets before obtaining an IP address, so no unicast session exists. UDP's connectionless, low-overhead delivery on ports 67/68 lets the four-step DORA exchange complete without TCP handshake delays, satisfying the requirement to identify applications that commonly use UDP.
- ✗
SSH
Why it's wrong here
SSH runs over TCP port 22 to guarantee ordered, reliable delivery of keystrokes and file transfers; UDP's connectionless datagrams suit DNS, DHCP and TFTP instead. The temptation is that SSH secures remote sessions, but transport reliability, not security, decides the protocol.
- ✗
SMTP
Why it's wrong here
SMTP uses TCP port 25 for reliable, ordered message delivery, so it is not a UDP application. UDP suits DNS, DHCP, SNMP, TFTP, and VoIP, where low latency outweighs reliability. SMTP is tempting because email is ubiquitous, but its transport requirement is TCP, not UDP.
- ✓
DNS
Why this is correct
DNS queries use UDP port 53 for standard resolution, since a single request-response datagram avoids TCP's three-way handshake overhead. This connectionless transport suits the small, fast lookups the question asks about, though DNS falls back to TCP for zone transfers and responses exceeding 512 bytes.
- ✓
NTP
Why this is correct
NTP relies on UDP port 123 for time synchronisation, tolerating occasional packet loss in exchange for low-latency, connectionless exchanges. This satisfies the stem's requirement to identify applications using UDP as their transport protocol, since NTP avoids TCP's handshake overhead entirely.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-901 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 200-901 exam.