Copyright (c) 2026 MindMesh Academy. All rights reserved. This content is proprietary and may not be reproduced or distributed without permission.
2.6.1. Address Structure
IPv4 Packet Header:
The TTL field decrements at each hop (router)—when it reaches 0, the packet is dropped and an ICMP "Time Exceeded" is sent back. This is how traceroute works.
IPv4 Address Structure
IP Address: 192.168.1.100
Binary: 11000000.10101000.00000001.01100100
Subnet Mask: 255.255.255.0 (or /24)
Binary: 11111111.11111111.11111111.00000000
|------Network------|--Host--|
Subnetting Quick Reference
CIDR to Subnet Mask:
| CIDR | Subnet Mask | Hosts per Subnet | Block Size |
|---|---|---|---|
| /24 | 255.255.255.0 | 254 | 256 |
| /25 | 255.255.255.128 | 126 | 128 |
| /26 | 255.255.255.192 | 62 | 64 |
| /27 | 255.255.255.224 | 30 | 32 |
| /28 | 255.255.255.240 | 14 | 16 |
| /29 | 255.255.255.248 | 6 | 8 |
| /30 | 255.255.255.252 | 2 | 4 |
Formula: Hosts per subnet = 2^(host bits) - 2 (subtract network and broadcast)
Enroll to unlock the 3 practice questions written for this section, so you can test what you just read while it is fresh.
Enroll to unlock the 4 flashcards for this section and review them on a spaced-repetition schedule.
Written byAlvin Varughese
Founder•18 professional certifications