📘 04-03: Core Protocols & Their Ports¶
📌 Application-Layer Services¶
| Protocol | Port(s) | Transport | Purpose |
|---|---|---|---|
| HTTP / HTTPS | 80 / 443 | TCP | Web |
| FTP | 20/21 | TCP | File transfer |
| SFTP | 22 | TCP | Secure file transfer (over SSH) |
| TFTP | 69 | UDP | Simple file transfer (configs/images) |
| SMTP | 25 (587) | TCP | Send email |
| POP3 / IMAP | 110 / 143 | TCP | Retrieve email |
| DNS | 53 | UDP/TCP | Name resolution |
| DHCP | 67/68 | UDP | IP configuration |
| SNMP | 161/162 | UDP | Monitoring / traps |
| NTP | 123 | UDP | Time sync |
| LDAP / LDAPS | 389 / 636 | TCP | Directory services |
| Kerberos | 88 | UDP/TCP | Authentication (AD) |
| RDP | 3389 | TCP | Remote desktop |
| SSH / Telnet | 22 / 23 | TCP | Remote CLI (secure/insecure) |
📌 Diagnostic & Infrastructure Protocols¶
| Protocol | Role |
|---|---|
| ICMP | Errors & diagnostics (ping, traceroute, "destination unreachable") |
| ARP | IP → MAC on the local segment |
| QUIC | Modern low-latency transport over UDP (HTTP/3) |
📌 Email Flow¶
- SMTP sends/relays mail between servers.
- POP3 downloads mail (usually removes from server) — single device.
- IMAP keeps mail on the server and syncs across devices.
Tip
Key idea — Know each protocol's port, transport (TCP/UDP), and job. SMTP sends; POP3/IMAP retrieve. ICMP powers ping/traceroute; ARP maps IP↔MAC.
See also: Ports & Protocols Reference, Secure Protocols & Encryption
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