IPv4 Addressing

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What is IPv4?

IPv4 (Internet Protocol version 4) is the fourth version of the Internet Protocol (IP). It uses a 32-bit address format, typically represented as four decimal numbers separated by dots (e.g., 192.168.1.1).

Each IP address has two main parts:

• Network portion

• Host portion

Step 1: Understand IP Classes (Classful Addressing)

Class	Starting IP	Ending IP	Default Subnet Mask	Usage
A	0.0.0.0	127.255.255.255	255.0.0.0	Large networks
B	128.0.0.0	191.255.255.255	255.255.0.0	Medium networks
C	192.0.0.0	223.255.255.255	255.255.255.0	Small networks
D	224.0.0.0	239.255.255.255	N/A (Multicast)	Multicast
E	240.0.0.0	255.255.255.255	N/A (Reserved)	Reserved

Step 2: Practical Example

Let’s take this IP address as an example: 192.168.10.17/28

Find the Class:

• Starts with 192 ⇒ Class C

• Default mask of Class C = 255.255.255.0

Classful or Classless?

• /28 is a custom prefix ⇒ This is classless addressing (CIDR - Classless Inter-Domain Routing)

Step 3: Convert Prefix /28 to Subnet Mask

• /28 means 28 bits are for the network ⇒ Subnet mask is:

11111111.11111111.11111111.11110000

In decimal ⇒ 255.255.255.240

Step 4: Calculate the Network Address

1. Convert IP and subnet mask to binary:

   • IP: 192.168.10.17 → 11000000.10101000.00001010.00010001

   • Subnet mask: 255.255.255.240 → 11111111.11111111.11111111.11110000

2. Perform bitwise AND:

11000000.10101000.00001010.00010001
AND
11111111.11111111.11111111.11110000
=
11000000.10101000.00001010.00010000
⇒ 192.168.10.16

Network Address = 192.168.10.16

Step 5: Calculate Broadcast Address

• Invert the subnet mask:

00000000.00000000.00000000.00001111 → 0.0.0.15

Add this to the network address:

192.168.10.16 + 0.0.0.15 = 192.168.10.31

Broadcast Address = 192.168.10.31

Step 6: Find First and Last Host

• First Host = Network Address + 1 = 192.168.10.17

• Last Host = Broadcast Address - 1 = 192.168.10.30

Step 7: Total Number of Hosts

• Formula: 2^(32 - subnet_prefix) - 2

• ⇒ 2^(32 - 28) - 2 = 2^4 - 2 = 14

Total usable hosts = 14

Summary

Item	Value
IP Address	192.168.10.17/28
Class	C
Subnet Mask	255.255.255.240
Network Address	192.168.10.16
Broadcast Address	192.168.10.31
First Host	192.168.10.17
Last Host	192.168.10.30
Total Hosts	14
Classful?	❌ Classless

Step 8: Python Code for an IP Calculator

Here’s a simple Python tool using the ipaddress module:

import ipaddress

def ip_calculator():
    try:
        # Get IP address and subnet mask from user
        ip = input("Enter IP address (e.g. 192.168.10.17): ").strip()
        subnet_mask = input("Enter Subnet Mask (e.g. 255.255.255.240): ").strip()

        # Create network using netmask
        network = ipaddress.IPv4Network(f"{ip}/{subnet_mask}", strict=False)

        print("\n--- IP Address Information ---")
        print(f"IP Address: {ip}")
        print(f"Subnet Mask: {network.netmask}")
        print(f"Prefix Length: /{network.prefixlen}")
        print(f"Network Address: {network.network_address}")
        print(f"Broadcast Address: {network.broadcast_address}")
        print(f"Total Hosts: {network.num_addresses - 2}")
        print(f"First Host: {list(network.hosts())[0]}")
        print(f"Last Host: {list(network.hosts())[-1]}")

        # Determine IP class
        first_octet = int(ip.split('.')[0])
        if 1 <= first_octet <= 126:
            ip_class = "A"
            default_prefix = 8
        elif 128 <= first_octet <= 191:
            ip_class = "B"
            default_prefix = 16
        elif 192 <= first_octet <= 223:
            ip_class = "C"
            default_prefix = 24
        elif 224 <= first_octet <= 239:
            ip_class = "D (Multicast)"
            default_prefix = None
        else:
            ip_class = "E (Reserved)"
            default_prefix = None

        print(f"Class: {ip_class}")
        if default_prefix:
            is_classless = network.prefixlen != default_prefix
        else:
            is_classless = True

        print(f"Classless Addressing: {'Yes' if is_classless else 'No'}")

    except Exception as e:
        print(f"Error: {e}")

# Run the calculator
ip_calculator()

Output

Enter IP address (e.g. 192.168.10.17):  172.16.11.24
Enter Subnet Mask (e.g. 255.255.255.240):  255.240.0.0

--- IP Address Information ---
IP Address: 172.16.11.24
Subnet Mask: 255.240.0.0
Prefix Length: /12
Network Address: 172.16.0.0
Broadcast Address: 172.31.255.255
Total Hosts: 1048574
First Host: 172.16.0.1
Last Host: 172.31.255.254
Class: B
Classless Addressing: Yes

Keywords

IPv4 addressing, subnet mask, IP calculator, network address, broadcast address, IP class, classful addressing, classless addressing, CIDR, prefix length, total hosts, first host, last host, IP range, IPv4 classes, netmask, private IP, public IP, IP subnetting, IP analysis, nerd cafe