After you purchase a web hosting service, your provider will send a welcome email with lots of information in it. One of them probably looks something like this: 220.127.116.11
Why would you need to know this bunch of numbers separated by dots about your web hosting service? This information is crucial for anyone (including you!) to send information to your server because that is the address of your server on the internet.
The internet is a global network of interconnected computers that communicate with other computers on the network by sending data to one another (your web server is essentially a computer with special software installed allowing it to serve information without your intervention after you set it up). How would a computer connected to the internet in Australia know where to send data to a computer connected to the internet in Brazil?
The basic idea is like sending a physical letter to your friend. You write the physical address on the envelope and the postman will locate your friend’s physical address and pass your letter to your friend at that address. That bunch of numbers you see in your welcome email is your server’s address on the internet. To be more precise, those numbers are your server’s Internet Protocol version 4 (IPv4) address.
How do you make use of an IPv4 address? For example, you have a VPS and you want to connect to it using SSH to command the VPS. In your SSH client, supply the IPv4 address and your SSH client will direct the request to connect to your server at that address. If you supply the wrong IPv4 address, your SSH client will send the request to the wrong place on the internet and you cannot contact your web server.
Your provider may also give you an Internet Protocol version 6 (IPv6) address, but that is less common for web servers. An IPv6 address looks something like this: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
So what is the difference between the IPv4 address and the IPv6 address? The IPv4 address system was developed in 1981 and provides about four billion unique addresses. That’s a huge number and was sufficient for most of the 80s and 90s when internet penetration was low.
Today, with so many smart devices ranging from mobile phones and smart home appliances connecting to the internet and requiring their own address, IPv4 will eventually be insufficient. The successor to IPv4 is IPv6, which was formalized in 1998. How many addresses can IPv6 handle? The answer: 3.4×1038.
However, we still predominantly use IPv4 for web servers because we have yet to practically run out of IPv4 addresses. Also, a web server on an IPv4 network can only send information to a computer on an IPv4 network. It cannot directly send information to a computer with an IPv6 address. If in doubt, just stick to using IPv4!