What is an IPv4 Address and How Does It Work?

Internet Protocol version 4 (IPv4) addresses play a crucial role in the way devices communicate over the Internet. This blog post aims to help you understand what an IPv4 address is, how it works, and the essential concepts associated with IPv4 addressing and communication.

Table of Contents

IPv4 Address Overview

An IPv4 address is a numerical identifier assigned to each device connected to the Internet. It is used to uniquely identify and locate devices on the global network, enabling communication between them. IPv4 addresses are part of the Internet Protocol, a set of rules that govern how data is sent and received over the Internet.

IPv4 is the fourth version of the Internet Protocol and has been widely used since the early days of the Internet. It employs a 32-bit addressing scheme, which allows for approximately 4.3 billion unique IP addresses. While this was initially considered more than sufficient, the exponential growth of the Internet has led to the eventual exhaustion of available IPv4 addresses, prompting the development of a successor, IPv6.

IPv4 Address Structure

An IPv4 address consists of 32 bits, divided into four 8-bit octets. Each octet represents a number between 0 and 255. To make the address more human-readable, the octets are written in decimal format and separated by periods. For example, an IPv4 address might look like this: 192.168.1.1.

IPv4 addresses are classified into different address classes (A, B, and C) based on their first octet, with each class having a specific range of values:

Note that the values 127 and 224-255 are reserved for special purposes and not included in the address classes.

Subnetting and Network Masks

Subnetting is a technique used to divide an IP address space into smaller subnetworks, allowing for more efficient management and allocation of IP addresses. Each IPv4 address can be split into two parts: the network portion and the host portion. The network portion identifies the specific network, while the host portion identifies the device within that network.

To determine which part of an IPv4 address represents the network and which part represents the host, a subnet mask is used. A subnet mask is a 32-bit number that shares the same format as an IPv4 address. When the subnet mask is combined with an IPv4 address using the bitwise AND operation, the result reveals the network address.

For example, if an IPv4 address is 192.168.1.10 and the subnet mask is 255.255.255.0, the network address would be 192.168.1.0. In this case, the first three octets represent the network portion, and the last octet represents the host portion.

IPv4 Routing and Communication

Routing is the process of selecting a path for data packets to travel between devices on different networks. Routers, specialized network devices, are responsible for forwarding packets between networks using routing tables. Routing tables contain information about the available paths and their associated costs, allowing routers to make informed decisions about the most efficient route for a packet to reach its destination.

When a device wants to communicate with another device on a different network, it sends a data packet to its default gateway (usually a router) with the destination IPv4 address. The router examines the destination address and forwards the packet to the next hop, which could be another router or the final destination device. This process continues until the packet reaches its intended recipient.

Address Resolution Protocol (ARP)

For devices to communicate within a local network, they need to know each other's physical (MAC) addresses. The Address Resolution Protocol (ARP) is used to discover the MAC address associated with a specific IPv4 address on a local network.

When a device wants to send a packet to another device on the same local network, it first checks its ARP cache to see if it already knows the MAC address of the destination device. If the destination MAC address is not in the cache, the sender broadcasts an ARP request to all devices on the local network. The device with the requested IPv4 address responds with an ARP reply, containing its MAC address. The sender then updates its ARP cache and proceeds to send the packet using the destination's MAC address.

Domain Name System (DNS) and IPv4

While IPv4 addresses are used by computers to identify and locate each other on the Internet, humans find it challenging to remember and work with long strings of numbers. The Domain Name System (DNS) was developed to make it easier for people to access resources on the Internet using human-readable domain names instead of numerical IP addresses.

DNS is a hierarchical, distributed database that maps domain names to their corresponding IP addresses. When a user types a URL into their web browser, the browser sends a DNS query to a DNS resolver, which then communicates with other DNS servers to find the IP address associated with the requested domain. Once the IP address is obtained, the browser can establish a connection to the webserver hosting the requested resource using that address.

Limitations of IPv4 Addresses

Despite its widespread use and success in facilitating communication over the Internet, IPv4 has some limitations, the most significant being the exhaustion of available IP address space. With only 4.3 billion unique IP addresses, IPv4 is unable to accommodate the rapidly growing number of devices connected to the Internet.

Several workarounds have been developed to address this limitation, such as:

While these workarounds have extended the lifespan of IPv4, they are not long-term solutions. The development of IPv6, with its vastly larger address space, aims to address the limitations of IPv4 and ensure the continued growth of the Internet.

Conclusion

Understanding IPv4 addresses and how they work is fundamental to grasping the basics of Internet communication. IPv4 addresses play a crucial role in uniquely identifying and locating devices on the Internet, enabling them to communicate with one another. While IPv4 has some limitations, it remains an essential component of the global network infrastructure. As the Internet continues to evolve, the transition to IPv6 will provide a more scalable and efficient addressing system to support the ever-growing number of connected devices.

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5 min. read
13 Oct 2022

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