What are DNS Records?
03 December 2016

What are DNS Records?

If you have a website or email on your own domain then you will have DNS records. But what are DNS records exactly, and how do they work? If you'd like to learn a bit more about DNS then read on.

First we need a little bit of background. Most of the internet works on two main protocols. TCP (Transmission Control Protocol) is about how data is transmitted around the internet, how it is formatted and packaged up for transmission. IP (internet Protocol) is about how individual devices (servers, mobile devices etc) are addressed and identified in the network. Together these two protocols are called TCP/IP and form the backbone of the internet. DNS records are closely linked to the IP part of the protocol.

The IP address of a device or server is an address that uniquely identifies the device on the internet (or local subnet). Most IPs are of type IPV4. An IPV4 address is usually written as 4 numbers (from 0-255). For example the IP address of the server running the Webfuel website is 23.102.12.43 (at the time of writing - it could change). For future reference there is a more modern IP address, called IPV6. IPV6 numbers are much longer. Here is an example IPV6 address: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. IPV6 is really only used in internal networks or networks between custom devices (see The Internet of Things).

All devices, websites, servers etc are "addressed" using IP addresses of the type above. While these numbers are great for computers, it's pretty clear that you're not going to remember that your website is located at 23.102.12.43. It's not really something you want to put on your business card! So, early in the life of the internet the Domain Name System (DNS) was invented.

At the simplest level all that DNS does is map "friendly internet names" such as www.webfuel.com, or www.bbc.com to IP addresses. You can type in a domain name, and the DNS system does the work of finding out which IP address the website is located at.

There is a bit more to it than that however. For example you may not only have a website, you may also have email, or even an FTP server. All of these things could be on different machines, and therefore at different IP addresses. To resolve this the DNS system also has the concept of different types of DNS record.

There are 3 main types of DNS record you will come across most commonly.

CNAME records map a domain name to another domain name. The first step in "resolving" the IP address of www.webfuel.com is that it is mapped via a CNAME to server.webfuel.net which is the domain name of our content management system.

A records map a domain name to an actual IP address. At the end of every chain of CNAMEs is an A record which is the final step in resolving the IP address of a website.

MX records map a domain name to a CNAME. So it's pretty much the same as a CNAME, but crucially the fact it is an MX record indicates this is a mapping to use for email. When an email server wants to send an email it will look for the MX record for that domain, rather than the CNAME. MX records also allow multiple records for the same domain name (whereas CNAME records do not). This allows us to set multiple mail servers for an email address, which can be used as fall back in case the primary mail server is offline. 

There are other types of records (TXT, SRV, AAAA, NS, PTR are ones you may come across) but these are less common and may be covered in a future post!

 

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