IPV4

four decimil numers separated by dots 10.1.2.3 dotted decimal notation. Each section is an octet. 8 bts of a binary numbe. Each is represented by a value of 0 to 265. gives total 32 bits. it

Network portion -

Host portion

subnet mask- continous stirngs of ones and zeros making up the host and network portion.

5 classes.

A 1 st octet value Devault mask 255.0.0.0 16.7 million hosts

B 128- 191. default mask 255.255.0.0 65536 hosts.

C 192-223 default mask 255.255.255.0 256 hosts.

D 224-239 multicast routing address. Logical address for a group of computers that can be multipcase.

E 240 255 experemtal, for R and D

Classless Mask. Used to borrow some of the host bits from an IPV4 to be used as a network portion.

ex 192.168.0.1. 255.255.255.0 if i only need 64 hosts use 255.255.255.192

Classless interdomain routing . CIDR

192.168.1.4/24

IPV4 Addressing (N10-009)

Dotted-Decimal Notation

Format: four decimal numbers separated by dots (e.g., 10.1.2.3).
Each section = octet = 8 bits → value 0–255 (not 265).
Total address length = 32 bits.

Network vs Host Portion

Split by the subnet mask (contiguous 1s for network, 0s for host).
Example: /24 (255.255.255.0) → first 24 bits = network, last 8 bits = host.

Classful Addressing (legacy but tested)

| Class | 1st Octet Range | Default Mask | Usable Hosts per Network* | | --- | --- | --- | --- | | A | 1–126 | 255.0.0.0 (/8) | 16,777,214 | | B | 128–191 | 255.255.0.0 (/16) | 65,534 | | C | 192–223 | 255.255.255.0 (/24) | 254 | | D | 224–239 | Multicast | n/a | | E | 240–255 | Experimental | n/a |

Usable hosts = 2^(host bits) − 2 (network + broadcast).

Note: 127.x.x.x reserved for loopback.

Private (RFC 1918) Ranges (Must Know)

Class A: 10.0.0.0/8
Class B: 172.16.0.0 – 172.31.255.255 (/12)
Class C: 192.168.0.0/16

Classless Addressing (CIDR)

CIDR = Classless Inter-Domain Routing → writes masks as /prefix (e.g., 192.168.1.4/24).
Lets you borrow host bits to create more subnets (VLSM).

Example (your scenario)

Start: 192.168.0.0/24 (mask 255.255.255.0) → host bits = 8 → 254 usable hosts.
Need ≈ 64 hosts → choose /26 (255.255.255.192)
- Host bits = 6 → 2^6 = 64, usable = 64−2 = 62 (fits “~64 hosts”).
/26 subnets of 192.168.0.0:
- 192.168.0.0/26 (hosts .1–.62, bcast .63)
- 192.168.0.64/26 (hosts .65–.126, bcast .127)
- 192.168.0.128/26 (hosts .129–.190, bcast .191)
- 192.168.0.192/26 (hosts .193–.254, bcast .255)

Exam Tip: When they say “needs 60–64 hosts,” pick /26.

Quick Subnet Cheat Table (High-Yield)

| Prefix | Mask | Usable Hosts | Block Size in 4th Octet | | --- | --- | --- | --- | | /24 | 255.255.255.0 | 254 | 1 | | /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 |

Memory Trick: “128, 64, 32, 16, 8, 4” are the block sizes for /25 → /30.

Must-Know Definitions

Subnet mask: Delimits network/host bits (contiguous 1s then 0s).
Network address: First address in subnet (all host bits 0).
Broadcast address: Last address (all host bits 1).
Gateway (router) IP: Typically first usable (.1) but can be any usable.

Flashcards

Q: Range of a single octet? A: 0–255.
Q: How many usable hosts in /26? A: 62.
Q: Private Class B range? A: 172.16.0.0–172.31.255.255.
Q: Formula for usable hosts? A: 2^(host bits) − 2.
Q: What does /24 mean? A: 24 network bits → 255.255.255.0.

Rapid Review Questions

You need at least 30 hosts per subnet. Smallest prefix? → /27 (30 usable).
First subnet of 10.0.0.0/26: network? broadcast? → 10.0.0.0, 10.0.0.63.
Which class has default mask /16? → Class B.

Want a 10-question mini-quiz or a one-page subnetting cheat sheet?