DNS explained (simplified)

Ok I’ve had lots of people ask me about domains, email etc and everyone over here seems confused and recently we’ve handled someone’s domain transfer and it all went wrong (I wasn’t involved). So I thought why not do a simple introduction/explanation for everyone. Please feel free to add any additional information to this post if you know anything about dns. I’ll keep it as simple as possible.

A domain name needs sets of Nameservers to be assigned to it in order to let everyone know on the internet where your site is. Once the internet knows who is responsible for that domain name, that Nameserver then can pass on more instructions on how to handle email and the web site. Easy so far yeah?

Right so now we have CNAME records (usually to create subdomains like home.domainname.co.uk or pop3.domainname.co.uk), “A” records which point to an IP address like “66.102.9.147” and a “A” record enables you to point to which server you would like to host the web site on. “MX” records handle all email traffic for that domain name, so it is like a pointer which points the email to the correct email server (Exchange or whatever).

Domains also have a TAG for UK domains which is basically a nominet registration tag, when you register with nominet you get one to identify your company and assign domain names so you can control the nameservers and registration details.

So lets say you have a client xyz and they just want to point their email from the domain name to their exchange server. What do you do? Well first job is to check where the tag is hosted. Visit www.nic.uk and enter xyz.co.uk in the whois box (NO WWW REMEMBER because that is a cname record). In fact if you put in www.google.co.uk in the whois box, the nominet system will warn you that you have entered a invalid domain. Now we have entered the correct domain xyz.co.uk it should show the registrant details amd the TAG, a ISP can control the TAG and the nameservers OR just the TAG and someone else hosts the nameservers.

We find that xyz.co.uk is hosted by us and is pointing to our nameservers. The next job then is to change the MX records to point to the exchange server, and MX record can also have a priority which allows you to assign multiple servers to handle email in case one of them goes down. Smaller numbers have higher priority, we assign the MX record to a.mx.myexchangeserver.co.uk. with a priority of 10 and b.mx.myexchangeserver.co.uk. with a priority of 20. If for some reason our mail server goes down we have a backup server in place. Most modern ISP’s let you control DNS through the control panel.

A useful utility to use is “nslookup”, this tool allows you to inspect a domains dns records, it is available on Windows, Mac, Linux and comes pre-installed on all. To use it go to the terminal in OX or the command prompt in Windows. Then type nslookup, this should give you a new prompt. enter the following:-

1. set type=mx
2. yourdomain.co.uk

The type flag lets you choose which DNS record to look at. Change it to the desired record (MX, A etc).

I hope this is helpful for someone