IP Addressing

Every device on the Internet needs a unique IP address so that packets can be routed to the correct destination. At A-Level you must understand IPv4, IPv6, the concept of subnetting, and the difference between public and private addresses.

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IPv4

IPv4 (Internet Protocol version 4) uses a 32-bit address, typically written in dotted-decimal notation — four decimal numbers (octets) separated by dots.

Example:  192.168.1.100

Binary:   11000000.10101000.00000001.01100100

Address Space

• 32 bits → 2^32 = approximately 4.3 billion unique addresses.
• This seemed enormous in the 1980s but is now insufficient for the number of devices connected to the Internet.

Structure: Network Part and Host Part

An IPv4 address is divided into a network part (identifies the network) and a host part (identifies the specific device on that network).

The subnet mask determines which bits belong to the network part and which belong to the host part.

IP Address	Subnet Mask	Network Part	Host Part
192.168.1.100	255.255.255.0	192.168.1	.100
10.0.0.50	255.0.0.0	10	.0.0.50