§1 OSI layers
| # | Layer | Examples |
|---|---|---|
| 7 | Application | HTTP, DNS, SMTP |
| 6 | Presentation | Encoding, encryption formats |
| 5 | Session | Session management |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP, routers |
| 2 | Data link | Ethernet, MAC, switches |
| 1 | Physical | Cables, signals |
§2 Common ports
§3 IPv4 essentials
§4 Worked examples
Example 1
How many usable hosts are in 192.168.10.0/26?
- 32 − 26 = 6 host bits.
- 2⁶ = 64 addresses; minus network and broadcast = 62.
Answer 62
! Common traps
- Treating 172.32.x.x as private — the private block stops at 172.31.255.255.
Coverage source: 2023 ICT Proficiency Certification Examination FAQs (file dated 14 Feb 2023) (third-party copy)