Internet Protocol (IP) and IPv4 Addressing

Definition

Internet Protocol (IP) is a network layer protocol used to uniquely identify devices on a network and enable communication between them. Every device connected to a network or the Internet must have an IP address.

Key Points

What is IP?

• IP (Internet Protocol) identifies devices on a network.
• It allows data packets to be delivered from a source to a destination.
• There are two major versions of IP:
  • IPv4
  • IPv6

Why IPv6? IPv6 was introduced because IPv4 addresses are limited and have nearly been exhausted due to the rapid growth of Internet-connected devices.

IPv4

Definition

IPv4 is a 32-bit address divided into 4 octets, with each octet containing 8 bits.

IPv4 Format

n.n.n.n

Example:

192.168.20.12

Each octet ranges from 0 to 255.

Network Part and Host Part

Every IPv4 address consists of two parts.

1. Network Part

• Identifies the network.
• Must be the same for every device in the same network.
• Determined by the subnet mask.

2. Host Part

• Identifies an individual device.
• Must be unique within the network.

Example:

IP Address : 192.168.20.12
Subnet Mask: 255.255.255.0

Here:

• Network Part: 192.168.20
• Host Part: 12

Subnet Mask

Definition

A subnet mask tells us which portion of an IP address represents the network and which portion represents the host.

Without the subnet mask, it is impossible to determine the network and host portions of an IPv4 address.

Subnet Mask Notations

The same subnet mask can be written in three formats.

Example:

255.255.255.0 = /24

IPv4 Address Classes

Class A

Characteristics

Reserved Addresses

Example network:

120.0.0.0

Example broadcast:

120.255.255.255

Note

• Network ID (NID) identifies the network.
• Broadcast Address sends data to every host on the network.
• Neither address can be assigned to a host.

Class B

Class C

Class D

Multicast

Multicast means sending data to a specific group of devices rather than to every device or to a single device.

Example:

A live online lecture sent only to students who joined a multicast group.

Class E

These addresses are reserved by the IETF (Internet Engineering Task Force) and are not used for normal Internet communication.

IPv4 Classes Summary

Loopback IP Address

Definition

A loopback address allows a computer to communicate with itself.

IPv4 Loopback

127.0.0.1

The entire 127.0.0.0/8 range is reserved for loopback, but 127.0.0.1 is the most commonly used address.

IPv6 Loopback

::1

Uses

• Testing the TCP/IP stack
• Testing applications
• Diagnosing networking issues
• Verifying the network interface without using physical hardware

IP Configuration

Devices can receive IP addresses in two ways.

1. Static (Manual) Configuration

Definition

The administrator manually configures:

• IP Address
• Subnet Mask
• Default Gateway
• DNS Server

Windows Steps

Run → ncpa.cpl
→ Network Adapter
→ Properties
→ Internet Protocol Version 4 (TCP/IPv4)
→ Properties
→ Select "Use the following IP address"

To view configuration:

ipconfig

Detailed information:

ipconfig /all

Advantages

• Stable address
• Good for servers, printers, and routers

Disadvantages

• Requires manual configuration
• Prone to configuration errors

2. Dynamic (Automatic) Configuration

Definition

A DHCP (Dynamic Host Configuration Protocol) server automatically assigns:

• IP Address
• Subnet Mask
• Default Gateway
• DNS Server

Windows Steps

Run → ncpa.cpl
→ Network Adapter
→ Properties
→ IPv4
→ Select "Obtain an IP address automatically"

Advantages

• Automatic configuration
• Easy management
• Reduces human error

Disadvantages

• Depends on a functioning DHCP server

Default Gateway

Definition

A Default Gateway is the IP address of a router (or another gateway device) that forwards packets from the local network to other networks, including the Internet.

Example:

PC → Router → Internet

Without a default gateway, devices can usually communicate only within their own local network.

DNS Server

Definition

DNS (Domain Name System) translates:

• Domain names → IP addresses
• IP addresses → Domain names (reverse lookup)

Example:

www.google.com
        ↓
142.250.x.x

Without DNS, users would need to remember IP addresses instead of domain names.

APIPA

Definition

APIPA (Automatic Private IP Addressing) automatically assigns an IP address when a device cannot contact a DHCP server.

Range

169.254.0.0 – 169.254.255.255

Characteristics

• Automatically assigned
• Temporary
• Indicates a DHCP problem
• Supports limited local communication only
• Does not provide normal Internet connectivity

Private IP Addresses

Definition

Private IP addresses are reserved for internal (LAN) communication and are not routable on the public Internet.

They are typically used behind a Network Address Translation (NAT) device.

Private IPv4 Ranges

These ranges are reserved by IANA (Internet Assigned Numbers Authority).

Example:

192.168.1.15

Public IP Addresses

Definition

A Public IP address is globally unique and reachable over the Internet.

Characteristics

• Assigned by an Internet Service Provider (ISP).
• Used on the Internet and WANs.
• Must be globally unique.
• Can communicate with other public IP addresses.

Example:

8.8.8.8

Why Is IPv4 Still Used?

Although IPv6 provides a vastly larger address space, IPv4 remains widely used because:

• It is simple and familiar.
• Most existing networks support IPv4.
• Many devices and applications still rely on it.
• Technologies such as NAT and Subnetting help extend the useful life of IPv4.

NAT (Network Address Translation)

Definition

NAT translates private IP addresses into public IP addresses, allowing many devices on a local network to share a single public IP.

Example:

Private IP
192.168.1.10
      ↓
Router (NAT)
      ↓
Public IP
203.x.x.x

Subnetting

Definition

Subnetting is the process of dividing one large network into multiple smaller subnetworks (subnets).

Benefits

• Better performance
• Improved security
• Efficient IP address usage
• Easier network management

Example / Code

Display IP Configuration (Windows)

ipconfig

Explanation

• ipconfig displays the current IP configuration of network adapters.

Display Detailed Information

ipconfig /all

Explanation

• Shows:
  • IP Address
  • MAC Address
  • DHCP Status
  • DNS Servers
  • Default Gateway
  • Lease Information

Common Mistakes

• Confusing an IP address with a MAC address.
• Assuming 127.0.0.1 communicates with other devices (it only refers to the local machine).
• Thinking private IP addresses are accessible directly from the Internet.
• Believing APIPA provides Internet access.
• Forgetting that the subnet mask determines the network and host portions of an IP address.
• Assuming Class D and Class E addresses can be assigned to hosts.

Short Exam Notes

• IP: Identifies devices on a network.
• IPv4: 32-bit decimal address (4 octets).
• IPv6: 128-bit hexadecimal address.
• Subnet Mask: Identifies the network and host portions of an IP address.
• Class A: 1–126, /8
• Class B: 128–191, /16
• Class C: 192–223, /24
• Class D: 224–239 (Multicast)
• Class E: 240–255 (Experimental)
• Loopback IPv4: 127.0.0.1
• Loopback IPv6: ::1
• APIPA Range: 169.254.0.0/16
• Private IP Ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
• Static IP: Configured manually.
• Dynamic IP: Assigned automatically by DHCP.
• Default Gateway: Connects a local network to other networks.
• DNS: Converts domain names to IP addresses.
• NAT: Translates private IPs to public IPs.
• Subnetting: Divides a large network into smaller subnetworks.