DNS & DNS Servers

By Joshua Erdman
Digital Foundation, inc.

Too often have I encountered networks that looked like a tree fort set up by children. This is what I was introduced to when I started working at my first Network Administrator job. The whole company's infrastructure was based on 3 servers. Each server would crash at least once a day, and they would be rebooted because of various memory leaks and mis-configurations that would severely affect performance and stability.

One of the servers had an IDE card installed because it was so old the IDE controller on the motherboard stopped working; this server happened to be the DNS server. It was a Pentium 90 with 96 MB of RAM running MetaInfo's MetaDNS. And this is where our story begins.

What are DNS Servers for?
How do domains work?

Being naturally curious of mind, I asked what DNS is for and how it worked. I knew about domain names and URLs and how you needed them to browse the web, but I did not understand the big picture, the hierarchy of it all. After getting many answers (all of them conflicting in some way or another) I realized that no one in this company actually knew what they were talking about. All they knew is that they need to put in the internet address they wanted and match it to the IP address of the web server for the Internet to be able to browse the website.

I bought a copy of DNS & Bind and read the first 2 chapters at least three times. I now give seminars on the subject; I use the analogy that DNS is like the Internet's Phone Book. Just like when you use a phone book and look up a phone number using a person's or business' name, you look up the web server IP address using the Domain Name.

It is DNS that keeps the Internet usable. If DNS did not exist you would be going to websites by typing in http://66.218.71.89 instead of http://www.yahoo.com Which is easier for you to remember?

The DNS HOWTO explains it like this:

"DNS is the Domain Name System. DNS converts machine names to the IP addresses that all machines on the net have. It translates (or "maps" as the jargon would have it) from name to address and from address to name, and some other things.

A mapping is simply an association between two things, in this case a machine name, like ftp.linux.org, and the machine's IP number (or address) 199.249.150.4. DNS also contains mappings the other way, from the IP number to the machine name; this is called a reverse mapping."

DNS Root Servers

Now that we have established a good analogy of DNS servers being a phone book equivalent, we must ask one question:

Since a phone book covers only a certain area or
city, is there a PARENT phone book or index available
that specifies which city phone book to look in for
each person?

The answer is yes, these are DNS servers as well, they are referred to as ROOT servers. Read my article that describes a typical DNS lookup to see how and when root servers are used.

In the next article I will go over The Big Picture and we will cover DNS implementation considerations such as redundancy, domain structure, and security. You also should read about Domain Records and what goes on during a DNS lookup.

References:

There is so much more to DNS, here we cover the Big Picture and give you a good foundation of Basic DNS concepts, to get more information about DNS, get the O'Rilley and Associates book, DNS & Bind it is a great resource.

Also read the article that explains the steps of resolving a domain name. I also have available my PowerPoint presentation I gave when speaking to the SLO Bytes PC User's group on DNS resolution that is basically written from this article.

Article last reviewed: 02/15/2005

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