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Transport choices: which of the following application services use UDP rather than TCP? (DHCP, SMTP, SNMP, FTP, HTTP, TFTP)

Difficulty: Easy

Correct Answer: 1, 3 and 6

Explanation:


Introduction / Context:
Different application protocols choose TCP or UDP based on their needs for reliability, ordering, and speed. Identifying which well-known services use UDP is a common exam and troubleshooting task in networking.



Given Data / Assumptions:

  • Candidates: DHCP, SMTP, SNMP, FTP, HTTP, TFTP.
  • UDP is connectionless, best-effort; TCP is connection-oriented and reliable.


Concept / Approach:
Recall common port/transport pairs: DHCP uses UDP (ports 67/68), SNMP uses UDP (161/162), and TFTP uses UDP (69). SMTP, FTP, and HTTP rely on TCP for reliability and ordered delivery.



Step-by-Step Solution:

DHCP → UDP (broadcast discovery and lightweight exchanges).SMTP → TCP (reliable email transfer on 25/587/465).SNMP → UDP (simple, low overhead management).FTP → TCP (control on 21, data on 20 or passive ports).HTTP → TCP (classic HTTP/1.1) though modern variants may use QUIC/UDP for HTTP/3, but the classic assumption is TCP.TFTP → UDP (simple, lock-step file transfer on 69).


Verification / Alternative check:
Remember mnemonic: “D, S, T” (DHCP, SNMP, TFTP) → UDP. Others (SMTP, FTP, HTTP) → TCP.



Why Other Options Are Wrong:
2 and 4: Both SMTP and FTP are TCP-based.
1, 2 and 4: Incorrect because SMTP and FTP are not UDP. All of the above: Obviously wrong; not all listed use UDP.



Common Pitfalls:
Confusing TFTP with FTP; the “T” stands for Trivial and uses UDP. Also, be cautious with modern HTTP/3 using QUIC over UDP; traditional exam contexts still map HTTP to TCP.



Final Answer:
1, 3 and 6

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