Idiot’s Guide to DNS

DNS is the system that ensures when we type an address into our browser, we get to see the page we want to see.

While lots of people are familiar with the acronym, I often see there’s a lot of confusion about what it is. This short article will give a quick and dirty explanation of what it is, how it works and why sometimes it seems to act oddly.

Quick introduction to DNS

DNS stands for Domain Name System. It’s powered by fairies who spend their whole time watching the address bar of your browser. When you type a web page address into your browser, the fairies find the website on the web and deliver it to you.

Actually, I lied about the fairies, but other than that, that’s not a completely inaccurate explanation of DNS.

Do you still receive a telephone directory? Before the web took off, every year we’d receive a thick book filled with all the phone numbers for the region we lived in.

We could look through by name and then narrow it down by address and find a phone number for a specific person.

DNS is much the same for the internet.

Every web server that hosts websites has an IP address. The equivalent of a phone number.

You can type an IP address into your browser and be connected to a web server, though often you’ll just see an error rather than a website. That may be because it’s common for multiple sites to use the same IP address and the server doesn’t know which site you want.

Also IP addresses aren’t easy to remember, unlike a website name. How many IP addresses like this, 83.35.10.219, do you think you could remember?

So DNS works like a phone book, but instead of books, the system uses DNS servers. There are many DNS servers distributed around the world.

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When you type a website address into your browser, you are then connected to a DNS server.

The DNS server searches its records for the website address you entered. If the server finds it, it returns the IP address of the website’s server.

Using that information, your browser connects to the server which returns the web page you wanted.

DNS propagation

Propagation is the process where the IP address for a domain is passed to all the DNS servers around the world.

This happens in two cases. When a new domain name is registered and when a domain name is moved to a new IP address.

The propagation process can take a while to complete. It used to be expected that it could take up to three days. In reality it’s usually quicker and can take just a few minutes in some cases for the DNS server you’re using to update.

Sometimes when you move a domain to a new IP address, something odd happens.

After waiting for the DNS to update, you find you’re connected to your new site. You start checking everything works and suddenly you click a link and you’re looking at the old site.

That can happen because you’re not always connected to the same DNS server. Because the servers can update their records at different times, while propagation is happening, different DNS servers may send you to different sites.

The figure below illustrates how this can happen.

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How to check DNS propagation

To an extent you’re in the dark as to how the propagation process is going. You can get an overview though using a site like DNS Checker (https://dnschecker.org/).

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Enter your domain name into the search field and leave the drop down (1) set to A unless you’ve been told otherwise.

That will show a selection of DNS servers around the world with a green check mark for those with a record for the domain.

Bear in mind that if you’re moving a domain, all the servers should show a green check mark. In that case, you need to check the IP address (2) that each server has returned.