What is an IP address?

The postal-address analogy

When you request a web page, your device sends a small parcel of data labelled with two addresses: yours (so the reply knows where to come back to) and the website's (so the request knows where to go). Every router along the way reads only the address, not the contents, and forwards the parcel one hop closer to its destination, exactly like a postal sorting office reading an envelope without opening it. An IP address is that label. It has no idea who owns the device, what's inside the parcel, or why it was sent; it only says where.

IPv4 and IPv6: two numbering systems

There are two versions of the addressing system in use side by side today:

• IPv4: four numbers from 0 to 255 separated by dots, e.g. 203.0.113.42. Designed in the early 1980s, it allows for about 4.3 billion unique addresses, which sounded limitless at the time but is now far fewer than the number of internet-connected devices in the world.
• IPv6: eight groups of hexadecimal digits separated by colons, e.g. 2001:0db8:85a3::8a2e:0370:7334 (double colons are shorthand for a run of zeros). Designed in the late 1990s specifically to fix IPv4's shortage, it supports roughly 340 undecillion addresses, enough to assign a unique address to every device ever likely to exist, with no need to share.
• Because IPv4 addresses ran out, most home internet connections today share a single public IPv4 address between every device in the house (see "private" addresses below), while IPv6, where supported, gives each device its own globally unique address directly.

Public vs. private: the address your router shows the world isn't the one on your laptop

Look at your laptop or phone's own network settings and you'll usually see something like 192.168.1.14 or 10.0.0.23. This is a private address, valid only inside your home or office network, reused by millions of other networks around the world at the same time (the same way many houses on different streets can all have a "number 12"). Your router translates between this private address and a single public address, the one visible to the rest of the internet and the one our IP lookup tool shows you, through a process called Network Address Translation (NAT). This is also why your router itself has its own separate address for managing its settings; see our router IP address guide if you need to find that one specifically.

Static vs. dynamic: does your address ever change?

Most home and mobile connections use a dynamic public IP address: your internet provider assigns you one from a shared pool, and it can change whenever your router restarts, reconnects, or simply after enough time passes on the provider's lease. A static IP address, by contrast, is fixed and never changes, typically reserved for servers, business connections, or a paid add-on some providers offer. Neither is inherently more secure; dynamic addressing is simply the default because it lets providers reuse a limited pool of addresses across many customers over time.

Who actually assigns IP addresses?

No single company owns the internet's address space. It's managed in a hierarchy:

• IANA (the Internet Assigned Numbers Authority) sits at the top, allocating large blocks of addresses to five Regional Internet Registries covering different parts of the world.
• Regional Internet Registries (like ARIN for North America, RIPE NCC for Europe, or APNIC for Asia-Pacific) allocate smaller blocks from their region to internet service providers and large organizations.
• Your internet provider then assigns individual addresses (or shares one via NAT) to its own customers, including you, which is why the "internet provider" field on our IP lookup tool almost always matches the company you actually pay for internet access.

Reserved ranges you'll see mentioned often

A few IPv4 ranges are set aside by convention and never appear as a real, routable public address:

• 10.0.0.0–10.255.255.255, 172.16.0.0–172.31.255.255 and 192.168.0.0–192.168.255.255: the private ranges reserved for local networks (see "public vs. private" above).
• 127.0.0.1: the "loopback" address every device uses to refer to itself, never sent over a network.
• 169.254.0.0–169.254.255.255: a self-assigned range a device falls back to when it fails to get a real address, usually a sign of a network problem.