Your public IP address: what is it, and what does it reveal?

Sooner or later someone asks for it. The supplier who has to give your office access to a server, the technician trying to work out why you cannot reach a dashboard, the bank that blocks a transaction “from an unrecognised IP”. And the question, “what is your IP?”, usually has a less obvious answer than it seems, because you have more than one.

Understanding what that address is, who gives it to you and what it says about you helps you answer properly and worry no more than you need to.

What an IP address is

An IP address is the number that identifies a device on a network, much as a postal address identifies a letterbox. Every time you open a website, your device sends a request with your address as the sender, and the server replies to that address.

Names such as einscube.com exist for people; underneath, the DNS system translates them into IP addresses. We cover that when discussing DNS propagation.

Public and private IPs

This is where most of the confusion lies.

A private IP is the one your device has inside your home or office, assigned by the router. It usually starts with 192.168., 10. or 172.16. to 172.31., reserved ranges that do not exist outside local networks. Your laptop, your phone and the printer each have their own, and an office down the road has devices with exactly the same ones.

A public IP is the one your internet provider assigns you and the one the rest of the world sees. Every device on your network goes out to the internet with it.

The mechanism that makes this work is called NAT (network address translation). The router takes each device’s requests, sends them out with the public IP as the sender and, when the replies arrive, remembers which device each one belongs to. It works like a switchboard: one number on the outside, many extensions inside.

When a supplier asks for “your IP” to grant you access to something, they almost always mean the public one. The private one is no use to them: they cannot see it.

IPv4 and IPv6

Two versions live side by side.

IPv4 addresses are four numbers separated by dots, such as 203.0.113.7. There are around 4.3 billion possible addresses, and they ran out years ago. That is why providers resort to sharing them: with carrier-grade NAT (CGNAT), several customers go out to the internet on the same public IP. If that applies to you, the IP you see is not yours alone, which matters for some set-ups, such as opening ports or being recognised on an allow-list.

IPv6 addresses are the long ones, with letters and colons, such as 2001:db8:85a3::8a2e:370:7334. There are so many that every device can have its own without sharing. Many connections already have both and use IPv6 whenever the server supports it; servers that do not will see your IPv4.

What your IP reveals, and what it does not

From your public IP, any server you visit can tell:

• Your provider, or the organisation that runs the connection, through its autonomous system: the block of addresses it has registered. It is the same information that reveals where a website is hosted, as explained in how to find out what a website is built with.
• The country, almost always correctly.
• An approximate city, often wrong. The databases that map address blocks to places tend to put you in the capital or wherever your provider keeps its equipment.

What it does not reveal:

• Your name, your postal address or your phone number.
• Which particular device on your network made the request.
• Your exact location.

The party that can link an IP to a specific customer at a given moment is the provider, which keeps those records and only hands them over under legal obligation. That is why IPs appear in servers’ access logs: they identify a connection, not a person.

Why your IP changes

Most home and small-office connections have a dynamic IP: the provider assigns it from an available pool and may change it when the router restarts or every so often. That is normal and does not signal any problem.

A static IP is a separate service, common on business plans. If you need a system to recognise you by your address every time, that is what you need. On a phone, the IP changes even more: it depends on the mast, the network and whether you are on mobile data or wifi.

What a VPN changes

A VPN encrypts your traffic to a server run by the VPN provider and goes out to the internet from there. The sites you visit see that server’s IP, not yours, and place you in whichever country it is in. It is useful on public wifi or for reaching the company network from outside.

Much the same happens, with some nuances, with corporate proxies and with privacy features in some browsers and operating systems. If a tool ever shows you an IP that looks nothing like what you expected, the first thing to check is whether a VPN or proxy is active.

What knowing your IP is good for

• Allow-lists. Many systems restrict access by IP: an application’s database, a website’s admin panel, a staging server, a client’s network. To let you in, the administrator needs your public IP, and it helps to know whether it is static or dynamic, because a dynamic one will need updating when it changes.
• Technical support. When a service blocks you or will not load, your IP lets the technician find your connection in their logs and see whether a firewall stopped you.
• Troubleshooting. Checking whether you go out over IPv6 or IPv4, whether the VPN is working, or which country a server thinks you are in, when a site shows you a language or content you did not expect.
• Excluding your own traffic from a website’s statistics, in the tools that allow it by IP.

Checking yours

Our what is my IP tool shows your public IP address as soon as it opens, whether IPv4 or IPv6, with a button to copy it, together with your provider and its autonomous system, the approximate location any server infers from it, and the HTTP and TLS versions of your connection. It is what any website you visit sees of you, no more and no less.

If you are giving your IP for an allow-list, look it up from the same network and the same device you will connect from, with the VPN set as you will use it. An IP taken from your phone is no good for the office.

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Your public IP says who provides your connection and, roughly, where from. It does not say who you are. Knowing how to read it saves you back-and-forth with support and gives you a realistic idea of what each site can learn from your visit.