What is an IP address?

Imagine sending a parcel

A parcel needs an address so it can be sent to the right place. When your phone sends or receives information, the network also needs addresses. These are called IP addresses.

Your phone might use an address such as 192.168.1.10 on your home Wi-Fi. The address helps information reach it on that network. It is not your phone number or your home’s street address.

A name and an address do different jobs

You remember a website’s name; your device uses an address to connect. It is a little like knowing a shop’s name but needing its address for a delivery.

Unlike a permanent name tag, a network address can change. When several devices in a home go online, a website may see the same shared address for all of them. An IP address alone does not tell you which person is using a device.

Two versions you will encounter

IPv4 and IPv6 are two versions of the addressing system. An IPv4 address is usually written as four numbers separated by dots, such as 192.168.1.10. IPv6 uses a different written form: groups of digits, which can include the letters A–F, separated by colons.

Computers store IPv4 addresses in 32 bits and IPv6 addresses in 128 bits. A bit is a 0 or 1; more bits allow many more possible addresses.

Your home network has its own context

Private IPv4 ranges are reserved for use inside private networks. One home and another can both use 192.168.1.10 locally. That number does not have to identify the same device in those separate networks.

Sharing an outward-facing address

A home router can let a phone and laptop share one public IPv4 address through address-and-port translation. Alongside each address, a port number helps distinguish separate conversations.

The router keeps a record of those conversations so replies for the phone go back to the phone and replies for the laptop go back to the laptop.

Address space is not the count of usable devices

IPv4 has 2^32 possible bit patterns. IPv6 has 2^128. These mathematical counts are not the number of publicly assignable devices: addressing includes reserved ranges, network structure, and different address scopes.

What a prefix means

A prefix describes the leading bits shared by a block of addresses. In 192.168.1.0/24, the first 24 of 32 bits are fixed. Eight remain, giving 2^8 = 256 values: 192.168.1.0 through 192.168.1.255.

For example, 192.168.1.10 belongs to that block; 192.168.2.10 does not. The 256 values are not a promise of 256 assignable device addresses: some values have special uses in a conventional subnet.

Translation changes the visible endpoint

With Network Address Port Translation (NAPT), the router changes addresses and port numbers and keeps mappings for return traffic. A phone and laptop can both open a TCP connection using local port 50000. The router can map them to different ports, such as 62001 and 62002, on one public IPv4 address.

That explains how replies can reach the right local connection. It does not mean an outside device can freely start a new connection to the phone: inbound access needs an appropriate mapping and applicable network permissions.

The diagnostic lesson

Ask which interface, which network, which address family, and which side of a translator you are observing. A private address shown in your device settings and a public address seen by an internet service can both be correct descriptions of different parts of the communication.