Copyright (c) 2026 MindMesh Academy. All rights reserved. This content is proprietary and may not be reproduced or distributed without permission.
2.7.1. Public vs. Private Addressing
RFC 1918 Private Ranges:
| Class | Range | Default CIDR | Addresses |
|---|---|---|---|
| A | 10.0.0.0 – 10.255.255.255 | /8 | 16.7 million |
| B | 172.16.0.0 – 172.31.255.255 | /12 | 1 million |
| C | 192.168.0.0 – 192.168.255.255 | /16 | 65,536 |
Special Addresses:
- Loopback (127.0.0.0/8): Always refers to "this device." 127.0.0.1 is localhost—used for testing TCP/IP stack without network access.
- APIPA (169.254.0.0/16): Automatic Private IP Addressing. Windows/Mac assign this when DHCP fails—it's a symptom, not a valid configuration.
⚠️ Exam Trap: Seeing 169.254.x.x means the device couldn't reach a DHCP server. This is a troubleshooting indicator. Questions may describe symptoms and ask for the cause—if you see this address range, DHCP failure is the answer.
IPv4 Address Classes (Legacy):
| Class | First Octet | Default Mask | Purpose |
|---|---|---|---|
| A | 1-126 | /8 | Large networks |
| B | 128-191 | /16 | Medium networks |
| C | 192-223 | /24 | Small networks |
| D | 224-239 | — | Multicast |
| E | 240-255 | — | Experimental |
Note: Classful addressing is largely obsolete—CIDR allows any prefix length—but the exam still tests class recognition.
Written byAlvin Varughese
Founder•15 professional certifications