How Domain Name Servers (DNS) Work

You just learned that the primary job of a domain name server, or DNS server, is to resolve (translate) a domain name into an IP address. That sounds like a simple task, and it would be, except for the following points:

With so much to handle, DNS servers rely on network efficiency and internet protocols. Part of the IP's effectiveness is that each machine on a network has a unique IP address in both the IPV4 and IPV6 standards managed by the Internet Assigned Numbers Authority (IANA). Here are some ways to recognize an IP address:

Web servers and other computers that need a consistent point of contact use static IP addresses. This means that the same IP address is always assigned to that system's network interface when it's online. To make sure that interface always gets the same IP address, IP associates the address with the Media Access Control (MAC) address for that network interface. Every network interface, both wired and wireless, has a unique MAC address embedded in it by the manufacturer.

Now, let's look at the other side of the DNS equation: domain names.

If we had to remember the IP addresses of all our favorite websites, we'd probably go nuts! Human beings are just not that good at remembering strings of numbers. We are good at remembering words, however, and that is where domain names come in. You probably have hundreds of domain names stored in your head, such as:

You'll recognize domain names as having strings of characters separated by dots (periods). The last word in a domain name represents a top-level domain. These top-level domains are controlled by the IANA in what's called the Root Zone Database, which we'll examine more closely later [source: IANA]. There are more than 1,000 top-level domains, and here are some of the most common:

In a domain name, each word and dot combination you add before a top-level domain indicates a level in the domain structure. Each level refers to a server or a group of servers that manage that domain level. For example, "howstuffworks" in our domain name is a second-level domain off the COM top-level domain.

An organization may have a hierarchy of sub-domains further organizing its internet presence, like "bbc.co.uk" which is the BBC's domain under CO, an additional level created by the domain name authority responsible for the U.K. country code.

The left-most word in the domain name, such as www or mail, is a host name. It specifies the name of a specific machine (with a specific IP address) in a domain, typically dedicated to a specific purpose. A given domain can potentially contain millions of host names as long as they're all unique to that domain.

The "http" part stands for Hypertext Transfer Protocol and is the protocol by which information is sent by the user to the website she is visiting. Nowadays, you're more likely to see "https" which is a sign the information is being sent by secure protocol where the information is encrypted. This is especially important if you're providing a credit card number to a website [source: EasyNews].

Later, when we look at how to create a domain name, we'll see that part of registering a domain requires identifying one or more name servers (DNS servers) that have the authority to resolve the host names and sub-domains in that domain. Typically, you would do this through a hosting service, which has its own DNS servers. Next, we'll look at how these DNS servers manage your domain, and how DNS servers across the internet work together to ensure traffic is routed properly between IP addresses.

Every domain has a domain name server handling its requests, and there is a person or IT team maintaining the records in that DNS server's database. No other database on the planet gets as many requests as DNS servers, and they handle all those queries while also processing data updates from millions of people every day. That's one of the most amazing parts of DNS — it is completely distributed throughout the world on millions of machines, managed by millions of people, and yet it behaves like a single, integrated database!

Because managing DNS seems like such a big job, most people tend to leave it to the IT professionals. However, by learning a little bit about how DNS works and how DNS servers are distributed across the internet, you can manage DNS with confidence. The first thing to know is what the purpose of a DNS server is on the network where it resides. A DNS server will have one of the following as its primary task:

DNS servers that perform the first task are normally managed by your internet service provider (ISP). As mentioned earlier, the ISP's DNS server is part of the network configuration you get from DHCP as soon as you go online. These servers reside in your ISP's data centers, and they handle requests as follows:

The second category of DNS servers mentioned above is typically associated with web, mail and other internet domain hosting services. Though some hardcore IT gurus set up and manage their own DNS servers, hosting services have made DNS management much easier for the less technical audience.

A DNS server that manages a specific domain is called the start of authority (SOA) for that domain. Over time, the results from looking up hosts at the SOA will propagate to other DNS servers, which in turn propagate to other DNS servers, and so on across the internet.

This great web of DNS servers includes the root name servers, which start at the top of the domain hierarchy for a given top-level domain. There are hundreds of root name servers to choose from for each top-level domain. Though DNS lookups don't have to start at a root name server, they can contact a root name server as a last resort to help track down the SOA for a domain.

Now that you know how DNS servers are interconnected to improve the name resolution process, let's look at how you can configure a DNS server to be the authority for your domain.

When you want to create a new domain name, you need to do the following:

Whether your SOA is somewhere else or on your own system, you can extend and modify your DNS settings to add sub-domains, redirect e-mail and control other services. This information is kept in a zone file on the DNS server. If you're running your own server, you'll probably need to manually edit the zone file in a text editor. Many registrars today have a web interface you can use to manage DNS for your domain. Each new configuration you add is called a record, and the following are the most common types of records you can configure for your DNS server [source: GoDaddy.com].

The following is an example of what a zone file might look like for those who are editing it directly in a text editor. Note that the center column (second item on each line) includes a record type from those listed above. When you see an "@" in the left column, it means that the record applies in all cases not otherwise specified:

@ NS auth-ns1.howstuffworks.com

@ NS auth-ns2.howstuffworks.com

@ MX 10 mail

mail A 209.170.137.42

vip1 A 216.183.103.150

www CNAME vip1

Typical users will probably get the most use out of MX and CNAME records. The MX records allows you to point your mail services somewhere other than your hosting company if you choose to use something like Google Apps for your domain. The CNAME records let you point host names for your domain to various other locations. This could include setting google.example.com to redirect to google.com, or setting up a dedicated game server with its own IP address and pointing it to something like gameserver.example.com.

You should understand that DNS is not a static concept. In late 2018, ICANN finally rolled out new security features for DNS. In short, those changes affected the cryptographic keys used in the Domain Name System Security Extensions (DNSSEC) protocol, known by techies as the root zone key signing key (KSK). The security improvements were necessary, says ICANN, because of the way networks are rapidly changing and expanding, in part due to the Internet of Things, which brings millions of new interconnected devices into the internet's fold [source: Cooney].

Those safety measures are incredibly important because criminal-minded hackers often try to tap into the DNS system to steal personal information or simply wreak havoc, for example, in attacks like DNS hijacking. That means defense-minded computer users and IT professionals alike must stay up to date on preventative measures to prevent DNS poisoning attacks and denial-of-service attacks, among others [sources: Greenberg].