What is an IP address?
An IP (Internet Protocol) address is an identifier assigned to every device connected to a computer network: computer, smartphone, router, server... It plays the same role as a postal address: it lets data know where to go on the network.
Public IP and private IP
A private IP address is only visible inside your own network (at home, behind your router). Several people around the world can have exactly the same private IP, without conflict, since it's only used locally. A public IP address, on the other hand, is unique across the whole of the Internet: it's what identifies your router (and therefore potentially every device connected behind it) from the outside.
Your router actually has two distinct network interfaces: one facing the Internet, carrying the public IP address, and one facing your local network (Wi-Fi, cable), carrying the private IP address. That's what lets it act as a go-between for the two worlds: it receives on its public IP, and forwards to each device on the local network via their respective private IPs.
Your device
Local network
Router
Private IP (192.168.x.x)
Internet
Public IP
IPv4 and IPv6
There are two versions of the IP protocol. IPv4, the older and still the most widely used, is
written as four numbers separated by dots (e.g. 5.196.181.117). It only allows for
about 4.3 billion addresses — not enough given the Internet's growth. IPv6 was created to solve
this shortage: it's written in a longer, hexadecimal form (e.g.
2001:4860:4860::8888), and offers a number of addresses so large it's practically
inexhaustible.
IPv4
- Short format: 5.196.181.117
- ~4.3 billion possible addresses
- The most common today
IPv6
- Long format: 2001:4860:4860::8888
- A virtually unlimited number of addresses
- Gradual rollout since the 2000s
What is a network range?
IP addresses aren't assigned one by one, but in contiguous blocks called network ranges (or
"subnets"). A network range is generally written in CIDR notation, in the form
address/prefix — for example 5.196.181.0/24 designates the 256
addresses from 5.196.181.0 to 5.196.181.255. The number after the "/"
(the prefix) indicates how many bits of the address are fixed: the higher it is, the smaller the
range. A /24 corresponds to 256 addresses, a /16 to more than 65,000,
and so on. The same information is sometimes expressed as a subnet mask (e.g.
255.255.255.0, equivalent to /24).
Our CIDR calculator automatically works out the network address, broadcast, mask and number of available hosts from any CIDR notation.
Static IP and dynamic IP
A static IP never changes. A dynamic IP is reassigned regularly by the service provider (every time the router restarts, or periodically). Most consumer connections use a dynamic IP; static IPs are mostly reserved for businesses or offered as an option. Get My Public IP tries to estimate this behaviour from the hostname associated with your address — see the guide on hostnames and DNS.
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