DNS Explainer

Please note that GOSS do not provide any DNS related services or advice. This article is a general introduction for background information.

DNS is the method by which traffic for registered domains can be routed to specific servers on the internet. Domain registration and DNS is the means by which you can type a memorable URL in to you browser and, all going well, arrive at the website you were expecting.

Registering a Domain

There are many domain registrars to choose from. Once you have completed the registration process, and if the domain is available and meets the requirements, then it is yours for a fee.

Whoever you used to register you domain with will usually provide an interface so that you can manage your domain. One of the settings that is usually able to be defined is the authoritative DNS server. This essentially tells the Internet which DNS server holds the authority on where to find various resources that are associated with your domain.

Now that you have an authoritative DNS server defined every other DNS server on the Internet, if configured correctly, can now find resources that belong to your domain such as your website.

Example

Say for example a citizen opens their browser and wants to go to your website, in this case we will use www.borchester.gov.uk.

The website will have a URL that is typed into the browser address bar and submitted by the user. Behind the scenes the browser will ask the operating system where to find this URL. Using the settings that are defined in the operating systems network settings the operating system will ask the defined DNS server for the IP.

It is very likely though that the DNS server defined in the network settings is not the authoritative DNS server, so the server will send a query to the root DNS server to find who has the authority to hold the records for the domain.

The root server in turn then queries the associated top level domain (TLD) server, in our example this is the server that holds the records for .uk. This server in turn then queries the next server, the second level domain (SLD) server .gov.uk. This server then continues to query the server until your authoritative server is reached which holds the record for www.borchester.gov.uk.

Now that the DNS server in the network settings now knows the location it can tell the operating system which in turn allows the browser to be able to connect directly with the web server that is hosting the web site and download the webpage.

Diagram

Although this seems like a long-winded way to handle requests it happens fairly quickly and once the DNS server receives the correct IP for the URL it will most likely cache it for some time so that subsequent queries are even faster.

DNS is Business Critical

The way in which DNS interacts with making a request for a web page makes it a very important element of infrastructure and therefore should be considered business critical especially if the website that is hosting the site is.

The root servers, TLDs and SLDs are backed by many servers and each have many layers of redundancy built in to the design. However, the authoritative DNS server that is chosen by the domain owner may not have such considerations put in place.

When choosing a server to act as the authoritative DNS server it is vital that due diligence is carried out to ensure the provider is trustworthy and has taken suitable actions to ensure a reliable service, it is the one part of the process that the domain owner has control over.