What is DNS

DNS stands for Domain Name System. Think of it as a filing system or database for all the domain names on the internet. What is a domain name? When you browse to a web address, such as k2.com, you instruct your computer to visit a particular "domain" - a human friendly representation of a particular location on the Internet. These names are sometimes referred to as host names. Host names are not case sensitive and can contain alphabetic or numeric letters or the hyphen. A host name is also the name provided within a local network to each individual computer. We most often use host names with reference to servers. Each organization that maintains a computer network will have at least one server handling DNS queries. That server, called a name server, will hold a list of all the IP addresses within its network, plus a cache of IP addresses for recently accessed computers outside the network. Each computer on each network needs to know the location of only one name server.

Computer networks don't communicate in terms of "names," but rather numbers. Each server that serves content, be it web sites, e-mail, file server, etc., has a special number assigned to it, called an IP address (IP stands for Internet Protocol). A computer network has no idea what k2.com is or how to find it, but if we used the IP address of the site, it would understand what the connection should be. Therefore, there needed to be a way to translate the domain (a human understandable name like k2.com), into terms that the computer network would understand, one based on IP numbers. This is what DNS does. DNS is a system whereby we can keep a registry of human friendly names mapped to network friendly numbers.

When visiting a website like k2.com, an Internet browser checks to see if it has been there recently, in which case the IP address might be cached or stored locally on the computer. If the IP address cache is not found, the computer looks outside to DNS servers provided by the corporate network or Internet Service Provider (ISP). If those servers can't provide the information they in turn look to a server farther upstream on the Internet. These searches are forwarded up the line until they find the address or determine that it doesn't exist. If the address is available, it is then passed back to your browser. If not, a message telling the browser that the host name or domain is not available is sent.

How DNS works

So, how does the process work? How does a domain name, something humans understand, get translated into a IP number, something that computer networks will understand? As mentioned in the previous section, each domain has to have something called a name server. This is a server that is designated as authoritative for answering queries regarding the domain, communicating what number goes to what domain.

Where does the process start? Technically, “.com” is a domain. Every "." in the domain name is a separator representing a different level. Thus, when an Internet browser asks for the number assigned to k2.com, the computer network first has to go to the name server for the “.com” domain and request the name server for the "k2" domain under it. Theoretically there can be an infinite number of levels. We could ask for anthony.tom.bob.k2.com, and the computer would start from the right side of the domain name, ".com," and ask for the name server authoritative for each level. There does not need to be that many name servers in the search, for if the k2.com name server knew the IP address of anthony.tom.bob.k2.com, it could just send that information through the network and the process would stop. But, if it didn't have all the information, it would tell my computer where the next link in the chain was. If at any time the process hits a name server that is supposed to be authoritative for its level and that name server does not know where to direct the search, it will return an error. If there is no such domain as anthony.tom.bob.k2.com, then when the internet browser attempts to view the site, an error will be returned at whatever link of the chain the name servers have no information. Whenever a computer connects to the internet, your ISP gives that computer the IP addresses of special servers designed to answer enquires from that computer about domains. These designated servers in turn get their information from ICANN.

ICANN and the Top Level Domains

ICANN stands for the Internet Corporation for Assigned Names and Numbers. All the concepts discussed above can be found in the ICANN's name, and thus we can infer that they manage the whole DNS process. ICANN sets up, manages and maintains all the authoritative name servers for the very top level domain, the domain that is to the farthest right of any address. These servers are always on and their addresses never change. Their only purpose is to start the whole search and convert procedure. These ICANN servers have a list of other servers, managed by different companies, which ICANN has authorized to be authoritative for the next step in the process, the "Top Level Domains" or TLDs. They would be the ".com", ".net", ".org", ".ac", etc. These servers are also referred to as ‘root servers’. ICANN is the organization at the very top of the tree, and they manage and delegate the whole name server process for everyone else.

For more information about the DNS system see -  DNS Beyond the Basics