Which pairing of a service with its default port number is correct?
LPIC-1 Exam 102-500, objective 109. Networking fundamentals easy
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The options
Not correct HTTPS on TCP 8080
Wrong. HTTPS defaults to TCP 443. Port 8080 is a common unprivileged alternative for plain HTTP used by application servers and proxies.
Not correct DNS on UDP 43
Wrong. DNS uses port 53. Port 43 is whois.
Not correct SSH on TCP 23
Wrong. SSH listens on TCP 22. Port 23 is telnet, the unencrypted protocol SSH replaced.
Correct SMTP on TCP 25
Correct. SMTP for server-to-server mail transfer uses TCP 25. Ports 587 (submission) and 465 are used for authenticated client submission.
Why
Ports worth memorising for this objective: FTP 20 (data) and 21 (control), SSH 22, telnet 23, SMTP 25, DNS 53, HTTP 80, POP3 110, IMAP 143, HTTPS 443. The authoritative local list is /etc/services, which maps these names to numbers.
Where this comes from
- Cited
- LPI exam objective 109.1
- What it says
- Know the default port numbers of common network services.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 109 and space the ones you get wrong.