There’s one area of ICT that still seems to baffle many IT people, managers and directors alike and that’s DNS. I must admit that it was one area I struggled with until about 1996 and I’m still no expert but I’m happy giving advice to clients on the basics that they should already know because without the DNS the internet just won’t work. It’s the phone book of the internet.
The easy parts are the common DNS records like A, CNAME and MX. Some of the newer additions like SRV and SPF are what they call text records and not so common, the former is essential if you’re deploying XMPP (Jabber IM) or VoIP (voice over IP) services but the latter is also important if you’re tackling email spam. Something many of my clients used to do, until they signed up with Cleartext.
So to get back to the subject of this article The DNS (Domain Name System) for Beginners, here’s a quick run down of the essentials in the order that you’ll likely to come across them.
|Type of DNS Entry||Example||Description|
|Domain Name||facebook.com||The name you would register to get your organisation or yourself online.|
|A Record||http://www.facebook.com||The part of a web address before the domain name, for example the ‘www’ in http://www.facebook.com. This isn’t required but has become the usual thing to do.|
|MX Record||mail.facebook.com 10
|MX records tell other organisations email servers where the email server is for your domain name. It needs an A record in place first, typically ‘mail’.There are generally three MX entries as in the example. The intention is to try the 10 value server first then the 20 etc.|
Two other things are worth remembering, the first that each record has a TTL (Time To Live) which tells DNS when to update from the source, so a good trick if you are changing any records is to change this to something really low like 3600 (seconds) a day before any change so that changes happen quickly. Once you are happy with the changes return the value to it’s default.
The other thing to consider is that generally you’ll be using your ISP’s DNS servers and ISP’s being what they are, cost cutting outfits they don’t put a lot of horsepower into these servers. You can often get better performance using a third party DNS provider, for example OpenDNS.
Using OpenDNS speeds up the process of looking up domains so your computers internet apps, like your web browser may appear to be a bit quicker. OpenDNS also have a paid option to filter out domains that are compromised by spammers, trojans and viruses etc so that’s a great side benefit.
If you want to read more then as always a good starting point is Wikipedia’s DNS entry or contact me and I’d be happy to help.