What Is an IP Address: Find Yours and Check Someone Else’s

Every login alert, hosting panel and server log mentions an IP address, and most of the time people copy it into a search box and move on. The interesting part starts when the same person discovers three different addresses for one laptop: one in the network settings, another on a "what is my IP" site, and a third in the router firmware update log. All three are correct, and the difference between them is the whole story of how the internet routes traffic.

What an IP address actually is

An IP address is a numeric label that identifies a device on a network running the Internet Protocol. The postal analogy is close enough to be useful: for a package to arrive, both ends need addresses, and every sorting center on the way needs to know where to forward the package next. The IP address does exactly that job for data packets. Routers read the destination address, consult their routing tables and hand the packet one hop closer to its target.

The familiar dotted notation belongs to version 4 of the protocol. Each of the four numbers occupies one byte and ranges from 0 to 255, so the whole address fits in 32 bits. That gives 2 to the power of 32 possible addresses, which is 4,294,967,296. When the protocol was designed this looked like an inexhaustible supply, but the internet kept growing and the global pool of free IPv4 addresses is now effectively exhausted, which is the main reason version 6 exists.

192 . 168 . 1 . 10

192 → 11000000
168 → 10101000
1   → 00000001
10  → 00001010

All 32 bits: 11000000 10101000 00000001 00001010
Total IPv4 addresses: 2^32 = 4,294,967,296

IPv6 widens the field to 128 bits. Addresses are written as eight groups of four hexadecimal digits, and the notation allows compression: leading zeros inside a group are dropped, and one run of all-zero groups can be replaced with a double colon. The address space scales to 2 to the power of 128, roughly 3.4 times 10 to the power of 38, a number so large that exhaustion is not a realistic concern.

• IPv4: 32 bits, four decimal numbers from 0 to 255, dotted notation, pool exhausted;
• IPv6: 128 bits, eight hexadecimal groups, compressible notation, room for decades;
• both versions run in parallel, and one device commonly holds addresses of both kinds at once;
• there is no direct translation between the two, they are separate addressing formats.

Public and private addresses

A laptop has one address on the home network and a different one on the internet, and this is a deliberate design rather than a quirk. Standard RFC 1918 reserved three ranges for private use: any home or office may reuse them freely, but these addresses are never routed on the public internet. A router bridges the two worlds: it holds a private address on the home side and a public one on the provider side, and for every outgoing request it swaps the internal address for the external one. The mechanism is called NAT, network address translation.

• 10.0.0.0 to 10.255.255.255: the largest private range, common in corporate networks;
• 172.16.0.0 to 172.31.255.255: a middle-sized range, also mostly organizational;
• 192.168.0.0 to 192.168.255.255: home routers almost always live here;
• 127.0.0.1: the loopback address, traffic to it never leaves the device;
• 169.254.x.x: a link-local address a device assigns itself when no DHCP server answers.

If an address starts with 10., with 172.16. through 172.31., or with 192.168., it is an internal address and says nothing about your location on the internet: millions of households use the same numbers at the same time. Mask sizes and range boundaries for such networks are easy to compute with a subnet calculator.

Finding the internal address

The operating system reports the internal address directly. On Windows the command is ipconfig, on Linux and macOS it is ifconfig or ip addr. Look for the IPv4 line of the adapter you are actually using, and note the default gateway next to it: that is your router. The same numbers appear in the router web interface, which is usually reachable at 192.168.0.1 or 192.168.1.1.

How to find your external IP

Neither the browser nor the operating system knows the external address. The provider assigns it to the router, and no settings screen on the laptop lists it. The address is only visible from the outside, which is why the universal method is to ask an external service: any "what is my IP" page sees the source address of your request and echoes it back.

A practical way is to open the IP lookup tool. It shows your external address, the provider, the country and an approximate city taken from a GeoIP database. Treat the location as a rough estimate: such databases are frequently off by tens or hundreds of kilometers, especially on mobile networks, so "approximate region" is the honest reading, not "your location".

What you can and cannot learn from someone else’s IP

An address reveals less than people expect. It is assigned to a provider, not a person: the same address can belong to one subscriber this month and another the next, and on a mobile carrier a single public address is shared by thousands of devices through carrier-grade NAT. GeoIP databases map address ranges to countries and cities from assorted sources, and they are regularly wrong.

• country: detected almost every time reliably;
• region and city: approximate, accuracy depends on the database and the network type;
• provider and the organization holding the range: registry data, usually exact;
• network type: mobile, hosting, residential, visible from the range owner;
• street address, house number and the name of the resident: not derivable from the IP at all, that data exists only at the provider and is released to authorized authorities.

Checking an address from an email or a log

Email records its journey in Received headers. They are read from the bottom up, from the sender toward the recipient, and each line names the server that handled the message next. Some webmail services additionally insert an X-Originating-IP header with the sender address. In web server logs the visitor address is the first field of every line. Two cautions apply: headers can be forged by whoever controls the sending software, and for bulk mailings the Received chain will show the mailing infrastructure rather than the author.

Received: from mail-out.example.org (mail-out.example.org
        [203.0.113.25])
        by mx.provider.net with ESMTPS; Sat, 8 Nov 2026 10:14:02 +0300

Received: from laptop-user (unknown [198.51.100.77])
        by mail-out.example.org; Sat, 8 Nov 2026 10:13:58 +0300

X-Originating-IP: [198.51.100.77]

Reading bottom-up: the message left from 198.51.100.77

When the sender field shows an address like name@site.ru, it helps to split the address into parts first and see which domain it actually belongs to. The sender domain and the mailing infrastructure domain often differ, which is behind many "the bank wrote from a foreign address" stories. The anatomy of a URL is covered in detail in a separate piece on parsing URLs into components.

Static and dynamic addresses

A dynamic address is a lease, not a possession. The router receives it from the provider over DHCP, and after a reboot or an expired lease it may get a different one. Inside the home network the same scheme repeats: the router hands out addresses from its own pool, so the laptop address is not guaranteed forever. A static address stays put; providers sell it as an option, while data centers include it by default because servers need a fixed point.

For websites static matters because of DNS: a domain name points at an address, and if the address changes, some requests keep landing on the old value until DNS caches expire. The binding is loose in the other direction too: one name can resolve to several addresses, and one address behind NAT can serve many names. A quick IP lookup after rebooting the router tells you whether your external address survived.

Why people hide their IP

Every site you visit sees your address, not as surveillance but as a routing necessity: the reply needs a destination. Still, the address together with GeoIP data exposes a rough region and lets sites link your visits across services. That is why some people route their traffic through a VPN or proxy: the site then sees the address of the intermediate server. The everyday motives are unremarkable: less region-based profiling, one stable address while traveling. None of it grants total anonymity, and the rules of particular services and the laws of your jurisdiction still apply.

Common mistakes

• confusing IP with MAC address: the MAC is a factory serial of the network card, it operates inside the local network and never reaches the internet;
• confusing IP with domain: a domain is a human-readable name, an IP is a numeric address, and DNS connects the two;
• calling 192.168.x.x your external address: that range is private and identical across millions of homes;
• assuming an IP leads to a street and a house: databases give a city with a margin of error, the exact address lives at the provider;
• expecting a dynamic address to survive a router reboot;
• reading the first Received line as the origin, when the chain should be read bottom-up.

Common questions

Can two people share the same external IP?

Yes, and not by coincidence. Carrier-grade NAT at mobile operators puts thousands of subscribers behind one public address. Dynamic assignment adds another layer: an address that was yours yesterday can be issued to a neighbor today. Shared addresses are common enough that abuse reports always ask for timestamps together with the address.

What does 127.0.0.1 mean?

It is the loopback address of the machine itself. Traffic to 127.0.0.1 never enters the network, the operating system handles it locally, which is why developers test applications against it before deployment. The whole 127.0.0.0/8 range is reserved for this purpose, but 127.0.0.1 is the conventional choice.

Does the IP change when switching from Wi-Fi to mobile data?

Always, because you switch providers. The home address belongs to your internet provider, the mobile address to the carrier. A lookup will show a different range owner and often a different city, since GeoIP entries for mobile networks are tied to the regional gateways of the operator.

Is it dangerous to share your IP?

In ordinary conversation or a support ticket, no: every site already sees it. Two situations deserve care. Games and direct-connection messengers can be flooded with junk packets if someone learns the address, and region-guessing from the address feeds crude profiling. A VPN or proxy addresses both, at the cost of routing your traffic through someone else’s server.

Why does GeoIP place me in the wrong city?

The databases bind ranges to locations through indirect signals: the registered office of the provider, gateway positions, measurement data. For a residential provider the error is usually within the region; for mobile carriers and large corporations the registration city can be a different region or even a different country. The limitation is in the data sources, not in your connection.