The port DNS uses — OS, DBMS & Networks Aptitude Question
The port DNS uses: Which well-known port does DNS use by default? Answer and worked solution on CodeKairo.
- Topic: OS, DBMS & Networks
- Section: Programming MCQs
- Difficulty: Easy
- Time target: 45 seconds
Question
Which well-known port does DNS use by default?
Options
- 20
- 25
- 53
- 110
Show the answer and the worked solution
Correct answer: C. 53
Worked solution
- Port 20 carries FTP data, port 25 is SMTP for sending mail and port 110 is POP3 for retrieving it.
- DNS name resolution runs on port 53 — over UDP for ordinary queries, and over TCP for zone transfers and responses too large for a datagram.
Answer: 53.
The idea
Learn the small set that appears in every paper: 20 and 21 FTP, 22 SSH, 23 Telnet, 25 SMTP, 53 DNS, 80 HTTP, 110 POP3, 143 IMAP, 443 HTTPS.
Shortcut. Three of the options are file or mail transfer ports (20 FTP data, 25 SMTP, 110 POP3), so the odd one out, 53, is DNS.
Common trap. 25 tempts because DNS MX lookups are bound up with mail delivery, but 25 is SMTP itself.