Domain Name System (dns) - Under The Hood

The domain name system is the glue of the internet

. It binds the text you type into your browser's location bar to the address that corresponds to your desired site. Without it, users would be forced to memorize sequences of up to twelve digits or even longer just to pull up Amazon(dot)com. But how does it all work? Where does this translation take place?

Background

The domain name system is distributed throughout the internet. It consists of "authoritative servers," each of which provides address translation capabilities for systems under its domain. Each subdomain under the root domain also has an authoritative server. Authoritative servers on the top of the domain hierarchy, such as the one assigned to domainname[dot]com, receive information regarding other domains on the internet from servers called root servers. Once a server is given the address of a domain name from a root server, it stores it for access in a DNS cache server by systems in its domain.

The DNS and You

So how does your computer interact with the domain name system to retrieve an address? In plain English, when you type an address into a program that accesses the internet, your operating system searches through a list it keeps of domains you've looked up previously. If the domain is in this list, the operating system gives the program the associated address. If not, your operating system sends a lookup request to your defined DNS server. This server then searches through the records it has stored from prior queries to find the translation for your particular query. If it finds one, it returns the address associated with the domain name to your computer, which can then communicate directly with the system at that address. If your local name server cannot find the domain name you entered, your request may be passed up the line to a higher-level server, which performs the same check. This process continues until the corresponding address is returned or an error is generated. This is why if you mistype a web address, it may take a few seconds for your query to get passed along the chain until it is determined that such an address does not exist in the DNS database. That explains how the name you type is translated to a physical address to which your computer can send data.

Digging Deeper

Is it really that simple? Not always. Host names and IP addresses do not always have a one-to-one relationship. There can be more than one host name per IP address and more than one IP address per host name. In the former situation, a host may only use one IP address but serve many "virtual hosts" beneath the top-level host. This is how popular web hosting sites work, where thousands of users can set up websites on the same system.

Conversely, multiple IP addresses can point to the same host. This helps a large and extremely popular site like Amazon.com to deal with the deluge of traffic it receives. This also allows critical sites to maintain connectivity even if one of its addresses is inaccessible.

The domain name system is taken for granted by billions of people around the world, but it is among the many components that work behind the scenes to support the internet we rely on every day.

by: Melissa Smich

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