Common UDP Ports for A+
Short answer
UDP supports small, quick exchanges such as queries, broadcasts, and time updates. Many infrastructure services rely on UDP because the simplicity and low overhead fit their use case. Technicians should look for scenario cues: automatic address assignment (DHCP), name resolution (DNS), time synchronization (NTP), lightweight file transfer (TFTP), device polling/traps (SNMP), and centralized logging (Syslog).
Why it appears on the exam
- Direct recall: Which port does DHCP use? (67/68) - Scenario-based: A device cannot resolve hostnames; which service and port should you check first? (DNS 53, UDP for queries) - Short analysis: Explain why DHCP uses UDP rather than TCP in most cases.
Key concepts
Concept 1
Required terms
DNS (53): Domain Name System: resolves hostnames to IP addresses; typically uses UDP for standard queries and TCP for larger transfers. DHCP (67/68): Dynamic Host Configuration Protocol: assigns IP configuration to clients; uses UDP ports 67 (server) and 68 (client). TFTP (69): Trivial File Transfer Protocol: simple, unsecured file transfer often used for device boot/config provisioning; uses UDP. NTP (123): Network Time Protocol: synchronizes clocks across devices; uses UDP.
Example
New laptop cannot get an IP address -> DHCP ports 67/68 (UDP).
Concept 2
How Common UDP Ports works
UDP supports small, quick exchanges such as queries, broadcasts, and time updates. Many infrastructure services rely on UDP because the simplicity and low overhead fit their use case. Technicians should look for scenario cues: automatic address assignment (DHCP), name resolution (DNS), time synchronization (NTP), lightweight file transfer (TFTP), device polling/traps (SNMP), and centralized logging (Syslog).
Example
Router logs not arriving at log server -> Syslog on 514 (UDP).
Concept 3
Common confusion
- Thinking UDP services cannot use TCP in any circumstance (some services fall back to TCP for large transfers). - Expecting guaranteed delivery from UDP-based logging or traps.
Example
Devices showing different times -> check NTP on 123.
Concept 4
Core 1 (220-1201) question cues
Direct recall: Which port does DHCP use? (67/68); Scenario-based: A device cannot resolve hostnames; which service and port should you check first? (DNS 53, UDP for queries); Short analysis: Explain why DHCP uses UDP rather than TCP in most cases.
Example
New laptop cannot get an IP address -> DHCP ports 67/68 (UDP).
Sample questions
Select an answer to reveal the explanation. For tracked practice and weak-area review, use the Cultiv8 app.
Q1.In an A+ question, this detail appears: New laptop cannot get an IP address -> DHCP ports 67/68 (UDP). Which option matches it?
Q2.A support ticket includes this clue: Router logs not arriving at log server -> Syslog on 514 (UDP). Which concept is being tested?
Q3.An A+ support scenario describes this situation: Devices showing different times -> check NTP on 123. Which answer fits best?
Practice this lesson in Cultiv8
The app adds tracked practice, targeted remediation, saved session history, and future readiness scoring.
Continue in Cultiv8