What is DNS?

We explain what DNS is, how it works and how outages can be avoided

Domain Name System (DNS) is a hierarchical naming system that's applied to every entity connecting to the internet or a private network, such as a device or service.

The technology acts as a mediator between the user and the web browser, as the former typically works with memorable domain name templates while the latter uses IP addresses to communicate with other services across the internet. In this sense, the DNS removes the need for users to remember unique IP addresses.

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Often referred to as the "phonebook of the internet", DNS allows users to stick to site addresses such as www.itpro.co.uk, instead of a string of ordered numbers, punctuated by dots in the case of IPv4, or colons in the case of IPv6.

How does DNS work?

The way DNS functions is rather straightforward, at least on the surface. That's because it hides a suite of complex processes that can be described as a conversation between different components. 

Such an exchange begins when someone types or copy and pastes a website address into their web browser's search or URL bar. That then signals to the computer or other devices – such as a tablet or smartphone – to issue a query over the internet aimed at a target server; that server is known as a  recursive resolver. 

In essence, this process is akin to the computer asking what the IP address is of the search query. In order to resolve this request, the server then issues further queries. 

The recursive resolver first issues a query to what's known as the root server, which acts like an index. From here, the root server is able to direct the recursive resolver to the correct top level domain (TLD) - a server that hosts the last section of the url, such as .com, .co.uk or .fr.

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From here, the recursive resolver will then be directed to the authoritative nameserver, which is able to provide the final piece of the puzzle by matching the whole url, i.e. www.itpro.co.uk, with its IP address, provided it has access to it, which is then returned to the original web browser.

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This whole process, while quite complex, only takes a matter of seconds to complete.

What is a DNS server?

DNS servers form the underlying infrastructure that provides makes up the domain name system. That infrastructure is actually formed from multiple servers comprising the root server, recursive resolver, the authoritative server – more commonly called the domain name server – and the TLD name server. 

There are 13 DNS root servers spread across the world that every recursive resolver knows how to contact. These are overseen by the nonprofit known as the Internet Corporation for Assigned Names and Numbers (ICANN) and decide which TLD name server the recursive resolver should contact based on the TLD of the URL.

The TLD name server, which is managed by a branch of ICANN known as the Internet Assigned Numbers Authority (IANA), will be one of two types. Either it has information on addresses that end in a generic TLD, such as .com, .org or .net, or it has information on addresses that end in country code TLDs, such as .cn, .za or .uk

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Finally, the domain name server/authoritative name server has specific information on the domain name it serves, which is how it resolves the final piece of the DNS query puzzle.

What happens when DNS fails?

Unfortunately, like other bits of tech that make up the internet as we know it, DNS failure is rather common.

It can be crop up in the form of a temporary issue during the process of transferring a domain to a new hosting provider, for example. Or it can be a more serious outage in cased by a cyber attack or damage to part of the network which causes DNS queries to not resolve.

The reason you will suffer from what appears to be an outage is usually the same though - the domain name doesn't match with the IP address or the match between the two can't be found.

Although this makes a DNS failure sound pretty straightforward and thus easy to solve, this may not be the case. It can also have a pretty severe impact on a business. For example, for any organisation hosting apps or services on the internet, a DNS failure can have significant productivity and financial impact, making the service unavailable to customers.

Although there are ways to fix a DNS failure, it's vital you have some kind of DNS failover implemented so if the DNS des suffer an outage, it can easily be switched over to another DNS server so the end user won't even know there's a problem.

Another option for keeping your systems and services up and running is to install some kind of DNS monitoring to make sure if there is a problem, you know quickly enough to fix the issue before (hopefully) your customers notice there's a problem.

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