The Everyday Service Protocols
Kite Studio's firewall has a list of "allowed" rules, and the auditor asks why each one is there: 443, 22, 587, 993, 123. Each number stands for a service the studio depends on — the web, remote administration, file transfer, email, even the clock. A network engineer reads that list the way a doctor reads a pulse.
The rule
Know every service by its job, its port, and whether it is encrypted.
| Job | Protocol | Port | Encrypted? |
|---|---|---|---|
| Web pages | HTTP | TCP 80 | No |
| Web pages, secured | HTTPS (HTTP inside TLS) | TCP 443 | Yes |
| Live two-way web app channel | WebSocket (starts as HTTP/HTTPS, then upgrades) | 80 / 443 | Yes when over 443 |
| Remote command line | SSH | TCP 22 | Yes |
| File transfer, old style | FTP | TCP 21 (plus a separate data channel) | No |
| File transfer, secured | SFTP (runs inside SSH) | TCP 22 | Yes |
| Sending email | SMTP | TCP 25 between mail servers, 587 for users submitting mail | With TLS, yes |
| Reading email | IMAP / IMAP over TLS | TCP 143 / 993 | 993 yes |
| Clock sync | NTP (SNTP is its simpler cousin) | UDP 123 | No |
A few notes that the table cannot hold:
- TLS is the encryption layer under HTTPS and many other secure protocols. It proves the server's identity with a certificate and scrambles the data so eavesdroppers see nothing useful. SSL is its retired predecessor; people still say "SSL certificate", but modern systems use TLS 1.2 or 1.3.
- WebSocket keeps one connection open so the server can push updates instantly, as in a live chat or a shared design board.
- SMTP sends, IMAP reads: SMTP pushes mail towards the recipient's server; IMAP lets Asha's mail app read and organise it there, synced across all her devices.
- NTP keeps every clock in step. Wrong clocks break TLS certificate checks and make logs from different devices impossible to line up. SNTP uses the same packets with simpler logic, fine for small devices.
The shortcut
Pair each clear-text protocol with its secure replacement: HTTP 80 → HTTPS 443, FTP 21 → SFTP 22, Telnet 23 → SSH 22, IMAP 143 → IMAPS 993. If an old port appears on a firewall rule, ask why the secure twin is not being used.
443 open to the web server
HTTPS, encrypted with TLS. Keep it.
A common mix-up: SFTP is not "FTP with TLS" (that is a different protocol, FTPS). SFTP is file transfer carried inside SSH, which is why it shares port 22.
Drills
Answer fast — trust the rule.
Which port does HTTPS use by default?
SFTP shares port 22 with which protocol?
Asha's mail app downloads and syncs her inbox. Which protocol does that?
The studio's server clock drifts ten minutes. What is most likely to break first?
Which protocol keeps one connection open so a web server can push live updates to the browser?
Remember
- Know every service by its job, its port, and whether it is encrypted.
- HTTP 80 → HTTPS 443, FTP 21 → SFTP 22, Telnet 23 → SSH 22, IMAP 143 → IMAPS 993.
- TLS replaced SSL; SMTP sends and IMAP reads; NTP (UDP 123) keeps clocks honest.