IP Addressing and Subnetting

1. IP Addressing

An IP address uniquely identifies a device on a network, enabling communication. IPv4 uses 32 bits, represented as four octets (8-bit numbers) separated by dots (e.g., 192.168.1.1). Each octet ranges from 0 to 255 (2⁸ = 256 values).

Example:

• Binary: 11000000.10101000.00000001.00000001
• Decimal: 192.168.1.1

2. IPv4 Address Structure

An IPv4 address has two parts:

1. Network Portion: Identifies the network.
2. Host Portion: Identifies the specific device on that network.

The subnet mask determines the boundary between these portions.

graph LR 
A[IPv4 Address] --> B(Network Portion); 
A --> C(Host Portion); 
D[Subnet Mask] --> B; 
D --> C;

3. Subnetting

Subnetting divides a large network into smaller, logical subnetworks (subnets). This improves:

• IP Address Efficiency: Better use of available addresses.
• Network Performance: Reduced broadcast traffic.
• Security and Management: Easier to isolate and manage network segments.

4. Subnet Mask

A subnet mask uses binary 1s to represent the network portion and 0s for the host portion of an IP address.

Example:

• Subnet Mask: 255.255.255.0
• Binary: 11111111.11111111.11111111.00000000

A bitwise AND operation between the IP address and subnet mask yields the network address.

Example:

• IP Address: 192.168.1.1
• Subnet Mask: 255.255.255.0
• Network Address: 192.168.1.0 (Result of bitwise AND)

graph LR
    A[192.168.1.1] -.AND.- B[255.255.255.0];
    B --> C[192.168.1.0];
    C --> D[Network Address];

5. CIDR Notation

CIDR (Classless Inter-Domain Routing) notation uses a forward slash followed by the number of 1s in the subnet mask.

Example:

• Subnet Mask: 255.255.255.0
• CIDR Notation: /24 (24 leading 1s)

6. Subnetting Calculations

Subnetting involves these calculations:

1. Number of Subnets: 2ⁿ (where ‘n’ is the number of bits borrowed from the host portion)
2. Number of Usable Hosts per Subnet: 2^m - 2 (where ‘m’ is the remaining host bits; subtract 2 for network and broadcast addresses)

7. Practical Subnetting Example

To create 4 subnets from 192.168.1.0/24:

1. Borrow 2 bits: This changes the subnet mask to /26 (255.255.255.192).
2. Resulting Subnets:

Subnet	Address Range	Usable Hosts
Subnet 1	192.168.1.0 - 192.168.1.63	62
Subnet 2	192.168.1.64 - 192.168.1.127	62
Subnet 3	192.168.1.128 - 192.168.1.191	62
Subnet 4	192.168.1.192 - 192.168.1.255	62

graph LR
    A[192.168.1.0/24] --> B(Subnet 1: 192.168.1.0 - 192.168.1.63);
    A --> C(Subnet 2: 192.168.1.64 - 192.168.1.127);
    A --> D(Subnet 3: 192.168.1.128 - 192.168.1.191);
    A --> E(Subnet 4: 192.168.1.192 - 192.168.1.255);

8. IPv4 Address Classes (Historical)

Historically, IPv4 addresses were divided into classes based on network size (largely obsolete with CIDR):

Class	Starting IP Range	Ending IP Range	Default Subnet Mask	CIDR Notation	Purpose
Class A	1.0.0.0	126.255.255.255	255.0.0.0	/8	Large networks
Class B	128.0.0.0	191.255.255.255	255.255.0.0	/16	Medium-sized networks
Class C	192.0.0.0	223.255.255.255	255.255.255.0	/24	Small networks
Class D	224.0.0.0	239.255.255.255	N/A	N/A	Multicast communication
Class E	240.0.0.0	255.255.255.255	N/A	N/A	Experimental use