What is an IP address?

9 November 2026

An IP address is a number that identifies a device's interface on a network that runs the Internet Protocol. Routers use it to deliver every packet to its destination. There are two versions: IPv4 addresses are 32 bits long and IPv6 addresses are 128 bits. An address is either public, visible to the sites you visit, or private, usable only inside your local network.

What the address does in every packet

Everything you send over the internet is split into packets, and each packet header carries two addresses: the source and the destination. A router does not read the packet's content. It looks at the destination address and decides which neighbour to hand the packet to. The next router does the same, until the packet reaches the destination network.

The server sends its reply to whatever source address it received. So a website always learns an address to reply to: either yours, or that of an intermediary acting for you.

An address belongs to an interface, not to a device or a person. A phone on Wi-Fi and mobile data at once has at least two interfaces and two addresses. A single interface can also carry both an IPv4 and an IPv6 address.

IPv4 addresses

RFC 791, published in 1981, defines the IPv4 address as a fixed four octets, or 32 bits. It is written as four decimal numbers from 0 to 255 separated by dots, such as 203.0.113.25. That gives 2³² possible addresses, about 4.3 billion.

Addresses are handed out in blocks written in prefix notation. 203.0.113.0/24 means the first 24 bits identify the network and the last 8 bits identify hosts inside it, so the block holds 256 addresses.

That total is no longer enough for the number of connected devices. On 25 November 2019 the RIPE NCC announced that it had run out of IPv4 addresses. Mobile networks deal with the shortage by sharing one address among many subscribers, as explained in What is CGNAT.

IPv6 addresses

RFC 8200 raises the address size from 32 to 128 bits, enough to give every device its own public address with no sharing. An IPv6 address is written as eight groups of hexadecimal digits separated by colons.

RFC 4291 sets the short form. Leading zeros in each group may be dropped, and one run of all-zero groups may become ::, once per address. So 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.

A local network usually receives a 64-bit prefix, and each device chooses the second half of its own address. Most operating systems also create temporary addresses that rotate, so a device is not known by the same address everywhere it goes.

Public and private addresses

A public address is unique on the internet and reachable from any network. A private address is reserved for local networks and can repeat in millions of homes, because public routers do not forward it.

RFC 1918 reserves three private IPv4 blocks. The IPv6 counterpart is the unique local range in RFC 4193. A few other blocks have special roles:

When a privately addressed device goes online, the router puts its own public address in place of the source, changing the port if needed. It then remembers the mapping so replies return to the right device. This is network address translation (NAT), and it is why websites see your router's address rather than your device's.

Addresses and ports

The address delivers a packet to the device, and the port number delivers it to the right program on that device. A web server usually listens on port 443, and your device picks a temporary source port for each connection.

A single connection is therefore identified by five items: the protocol, the source address and port, and the destination address and port. That is how one device can hold hundreds of connections to the same server without their replies getting mixed up.

The same idea lets a home router, or a provider, put many devices behind one public address and tell them apart by port.

Who hands out addresses

IANA manages the global pool and gives large blocks to five regional registries. The RIPE NCC covers Europe and the Middle East, including Syria. The registries assign blocks to providers, and the provider gives each subscription an address.

An address can be static, never changing, or dynamic, assigned anew on each connection. Most home connections and mobile networks use dynamic addresses. A static address is usually requested to host a service that others connect to.

What your address reveals

Every server you connect to sees your public address. From it anyone can look up the provider and the network it belongs to, known as the autonomous system number (ASN). The country and city can also be estimated, often wrongly, as covered in IP geolocation.

The address alone carries neither your name nor your street. The provider, however, knows which subscription used an address at a given time. On shared networks it also needs the port number and the exact time to tell subscribers apart.

How to find your addresses

Your public address is what websites see, and the tool linked at the end of this page shows it. Your private address comes from the operating system:

ip -4 addr show     # Linux: IPv4 addresses
ip -6 addr show     # Linux: IPv6 addresses
ipconfig            # Windows: all interfaces

Compare the WAN address on your router's status page with your public address. If they differ, there is another layer of address translation after your router, usually at the provider. If the tool shows an IPv6 address, your network supports it and sites may use it instead of IPv4.

Controlling the address websites see

• An intermediary changes the visible address. With a VPN or proxy, websites see the intermediary's address and the intermediary's operator sees yours. Pick a provider whose logging policy you understand.
• Cover both versions. If a tunnel carries only IPv4 and your device has an IPv6 address, some connections may leave outside the tunnel. See IPv6 leaks.
• Watch the browser. WebRTC can expose a device's addresses to a web page, as explained in WebRTC leaks.
• Do not open ports you do not need. Port forwarding on the router makes a device reachable from the internet at your public address.

syriaproxy addresses

With syriaproxy, your traffic leaves from real IPv4 addresses on Syriatel's 4G network inside Syria. Syriatel subscribers share them behind the carrier's address translation. The network is IPv4 only, so IPv6 is blocked inside the tunnel.

FAQ

Check your public IP along with the provider and approximate location websites see.