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Learn · Lesson 2

What is an IP address?

If a domain name is the name on the shopfront, an IP address is the street address the delivery driver needs. You’ll rarely type one, but every domain you set up ends up pointing at one.

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The short version

  • An IP address is the number that identifies a device on a network, so data knows where to go.
  • There are two kinds in use: IPv4 (203.0.113.10) and IPv6 (2001:db8::10). The internet runs both side by side.
  • Addresses are either public (reachable from anywhere) or private (only inside your own network).
  • Your domain doesn’t come with an IP address. Its DNS records point at whichever servers you choose, and you can change them.

The number behind the name

IP stands for Internet Protocol, the set of rules for moving data between networks. Every device that takes part, whether a web server, your phone or the office printer, needs an address so that data can be sent to it and replies can find their way back.

People use domain names; machines use IP addresses. The DNS is the directory that translates one into the other, every time you open a website or send an email.

IPv4 and IPv6

There are two versions of IP address in everyday use, and you’ll meet both.

 IPv4IPv6
Looks like203.0.113.102001:db8::10
Written asFour numbers from 0 to 255, separated by dotsGroups of letters and digits (hexadecimal), separated by colons
Size32 bits: about 4.3 billion addresses128 bits: more than anyone will run out of
DNS recordAAAAA

IPv4 came first, and 4.3 billion addresses turned out to be too few for a world where every phone, fridge and doorbell is online. IPv6 is the fix. In the words of its specification, RFC 8200, “IPv6 increases the IP address size from 32 bits to 128 bits”.

The two aren’t compatible, so the internet runs both at once. Many servers have one of each, which is why a domain often has an A record and an AAAA record. If your host only gives you an IPv4 address, that’s fine: an A record on its own works.

A double colon in an IPv6 address is shorthand for “all zeros in here”, so 2001:db8::10 is the short way of writing 2001:0db8:0000:0000:0000:0000:0000:0010.

Public and private addresses

Not every address is reachable from the whole internet. Three blocks of IPv4 addresses are set aside for private networks by RFC 1918, and they’re reused in millions of homes and offices:

Private rangeWhere you’ll see it
10.0.0.0 to 10.255.255.255Larger office and company networks
172.16.0.0 to 172.31.255.255Company networks, some cloud setups
192.168.0.0 to 192.168.255.255Almost every home router

Your router holds one public address for the whole building and hands out private ones to the devices inside. A web server, on the other hand, needs a public address, because strangers have to be able to reach it.

Private addresses inside a network, public addresses on the internet A laptop, phone and printer inside a home or office network each have a private address starting with 192.168. They share the router's single public address, 203.0.113.25. Across the internet, one web server at the public address 203.0.113.10 hosts three different websites. INSIDE YOUR NETWORK: PRIVATE ADDRESSES Laptop 192.168.1.20 Phone 192.168.1.21 Printer 192.168.1.30 Your router public: 203.0.113.25 The internet: public addresses only One web server 203.0.113.10 hosting several websites on that one address: yourname.com.au example.com example.org
Private addresses stay inside the building. Out on the internet, everything travels between public addresses, and one public address can serve many websites.

A quick sanity check. If you’re ever told to point your domain at an address starting with 192.168. or 10., stop. That’s a private address. It will work from inside that one network and nowhere else.

One address, many websites

An IP address identifies a server, not a website. On ordinary web hosting, one server with one address holds hundreds of sites. When your browser connects, it tells the server which name it wants, and the server hands back the matching site.

Two things follow from that:

  • Typing your site’s IP address into a browser usually won’t show your site, because the server doesn’t know which of its sites you mean.
  • “Our website shares an IP address with other businesses” is normal, not a fault.

One name, many addresses

It works the other way too. Busy sites run on many servers, so a lookup can return several addresses, or different addresses depending on where in the world you’re asking from. If two people look up the same big-name site and get different numbers, nothing is broken.

Fixed and changing addresses

A static address stays the same. Servers have these, because DNS records need something stable to point at. A dynamic address can change from time to time, and that’s what most home internet connections get. It’s one reason websites live at hosting companies and not on a computer under someone’s desk.

Who hands them out?

Nobody picks their own public address. They’re handed down a chain. At the top, IANA allocates large pools “to the RIRs according to their needs”. The RIRs are five Regional Internet Registries; the one for the Asia/Pacific region, including Australia, is APNIC. From there, addresses go to internet providers and hosting companies, and they assign one to you or your server.

In practice: your web host tells you your server’s address, and your internet provider looks after the one at your home or office.

Where IP addresses turn up in your DNS

When you manage a domain, you’ll meet IP addresses in a few places:

  • A and AAAA records: “this name lives at this address”. Your web host gives you the address, and you put it in the record.
  • SPF records: a list of the servers allowed to send email for your domain, sometimes written as addresses.
  • Glue records: only if you run your own nameservers.

All three are covered in DNS records explained. The key idea is that your domain doesn’t have an IP address. Its records point at one, and when you change hosts you change the record. The name stays put.

The addresses in these lessons are examples from ranges kept for documentation. They don’t lead to real servers.

Terms in this lesson

IP address
The number that identifies a device or server on a network, so data knows where to go.
IPv4
The older, shorter kind of IP address: four numbers separated by dots, like 203.0.113.10.
IPv6
The newer, much longer kind of IP address, written with colons, like 2001:db8::10.
Private address
An IP address that only works inside one home or office network, such as anything starting with 192.168..
A record
A DNS record that points a name at an IPv4 address, such as 203.0.113.10.
AAAA record
The same as an A record, but for an IPv6 address.
APNIC
The Asia Pacific Network Information Centre: the regional body that hands out IP addresses in the Asia/Pacific region, including Australia.

Every term, in full, is in the glossary.

Sources

All read on 2 October 2026.

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