DNS and You - Part I

Everyone should get to know DNS - Domain Name System - even if it's on a beginner level. It's what will help you from panicking when you suddenly lose visibility with your mail server or people stop seeing your website. DNS acts like a multiple-entry phone book listing. Imagine your phone book and then imagine that it gives your phone, fax, cell, physical address and/or your earth coordinates. However I want to interact with you - this multiple-listing phone book tells me how to do it. DNS is what translates your www.domain.com address into a xxx.xxx.xxx.xxx IP address that your computer understands. DNS is the phone book of the Internet, and like regional yellow books, what you get will vary based on when or where you ask the question.

When your public internet website is separate from the rest of your organization - as in, you don't host your own content, you pay someone like Godaddy to do it for you - this creates its own little problem. For instance, you own domain.com and this covers all kinds of stuff, www.domain.com, mail.domain.com and, oh yeah, any of your devices that exist on your internal network will also be called workstation.domain.com or printer.domain.com. Domain.com has a lot of disparate parts that are probably not on the same server or even in the same location. How do we pull it all together? The answer is DNS. DNS will store all of this information and then provide it to your workstation or laptop when it is asking where it can go to get a specific thing - mail, printing, files, etc.

Now let's add a new wrinkle - Not every workstation in your organization has a public IP address, not every DNS request is asking for a public Internet address. This is the difference between external and internal DNS. Rather than making every workstation go out to the Internet when it wants something on the internal network and making every device on your internal network visible on the external, Internet-based, space - we use internal DNS. We handle that by making a server responsible for looking up IP addresses in your internal network - printers, servers, other workstations - this internal DNS server will manage where they are, not an external one. Additionally, this internal DNS server will be responsible for getting public IP addresses from external DNS servers - rather than 100 workstations making DNS requests, one server handles this job. This not only cuts down on traffic on your WAN link, the internal DNS server can store frequently-looked up addresses and make getting Internet traffic faster for you.

The differences between external and internal DNS can cause a lot of havoc. When these two address books disagree, the usual result is that some people will see your website and others won't. Some people can send email and others can't. We'll talk about some basic problems and solutions to DNS-related issues in Part II.