IP addresses

What is an IP address and why is it needed?
An IP address (Internet Protocol address) is a unique numerical identifier assigned to every device on a network. It functions like a postal address, ensuring that data packets sent across the Internet are delivered to the correct device. Every packet contains both a source and destination IP address. Routers use this addressing information to forward packets along the correct path. Without IP addresses, devices would have no way to locate each other, and communication between computers would not be possible.

What is IPv4 and how does it work?
IPv4 is the original version of the Internet Protocol and is still widely used today. It uses a 32-bit binary number divided into four 8-bit segments called octets, written in decimal format separated by dots (e.g. 192.168.1.). Each octet can range from 0 to 255. IPv4 allows for about 4.3 billion unique addresses. However, due to the explosive growth in Internet-connected devices, this address space has become nearly exhausted. IPv4 remains common, but its limited capacity is the reason the newer IPv6 system was introduced.

What is IPv6 and why is it needed?
IPv6 is the newer version of Internet Protocol addressing, designed to replace IPv4 and solve its address exhaustion problem. IPv6 uses 128 bits, written as eight groups of four hexadecimal digits separated by colons (e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334). It supports over 3.4 × 10³⁸ possible unique addresses, which is enough to supply every device on Earth for many decades. IPv6 also simplifies routing and includes improved built-in security features. Its enormous address space makes it essential for the continued growth of the Internet.

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What is the difference between public and private IP addresses?
Public IP addresses are globally unique and are assigned by an Internet Service Provider (ISP). They are routable on the Internet and used to identify networks and devices publicly. Private IP addresses are used only within local networks like homes or schools. They are not routable on the Internet, and are instead translated into the public IP address of the router using Network Address Translation (NAT) when accessing the Internet. This system allows many devices to share a single public IP while still being individually identifiable inside the local network.

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What is the difference between classful and classless addressing?
Classful addressing is an older system where IPv4 addresses were divided into fixed classes (A, B, C, D, and E). Each class reserved a certain number of bits for the network ID and the remaining bits for the host ID. For example, Class A used 8 bits for the network and 24 for the host. This caused inefficient use of the address space.
Classless addressing, known as Classless Inter-Domain Routing (CIDR), replaced classful addressing. It allows network administrators to specify how many bits are used for the network ID by adding a suffix (e.g. /24). This makes addressing far more flexible and efficient, allowing networks to be sized appropriately without wasting unused addresses.

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Summary

IP addresses uniquely identify devices on a network so data can be routed correctly. IPv4 uses 32-bit dotted decimal addresses and is nearly exhausted, while IPv6 uses 128-bit hexadecimal addresses and provides an almost limitless supply. Public IPs are globally unique and routable, while private IPs are used inside local networks and translated via NAT. Addressing was once classful but is now classless using CIDR, which allows more efficient allocation of the IPv4 address space.