What a DNS Server Is and How It Works

 

What is a DNS server?

 Domain Name Server (s) (DNS) are the Internet’s equivalent of a phone book. They maintain a directory of domain names and translate them to Internet Protocol (IP) addresses. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts.

 

 

Fig: DNS Server

DNS Root Servers

DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top level of the hierarchy, so-called root servers store a complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers that have become somewhat famous for their special role. Maintained by various independent agencies, the servers are aptly named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in London, UK and one in Stockholm, Sweden.

How DNS Server Works

The DNS is a distributed system, meaning that only the 13 root servers contain the complete database of names and addresses. All other DNS servers are installed at lower levels of the hierarchy and maintain only certain pieces of the overall database.
Most lower level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example, Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other domains. Your ISP also maintains DNS servers as part of your Internet connection setup.
DNS networking is based on the client / server architecture. Your Web browser functions as a DNS client (also called DNS resolver) and issues requests to your Internet provider’s DNS servers when navigating between Web sites.
When a DNS server receives a request not in its database (such as a geographically distant or rarely visited Web site), it temporarily transforms from a server to a DNS client. The server automatically passes that request to another DNS server or up to the next higher level in the DNS hierarchy as needed. Eventually the request arrives at a server that has the matching name and IP address in its database (all the way to the root level if necessary), and the response flows back through the chain of DNS servers to your client.

DNS Server (s) and Home Networking

Computers on your home network locate a DNS server through their Internet connection setup properties. Providers give their customers the public IP address(es) of primary and backup DNS servers. You can find the current IP addresses of your DNS server configuration via several methods:

• on the configuration screens of a home network router
• on the TCP/IP connection properties screens in Windows Control Panel (if configured via that method)
• from ipconfig or similar command line utility

Publicly available DNS tools can be used to search for information related to Internet domains. Professional network administrators use these same basic tools on business networks.

The difference between Content and Resolving DNS services

DNS servers to provide a single service: to convert names addresses. Many DNS servers around the internet operate in this simplistic manner. DNS servers should provide one of two services: content or resolution services.

Content servers

A content server is one which contains authoritative DNS records. These records are just single pieces of information such as:

• the name a website referring  to its IP address
• the domain of a website should have its mail delivered to its address
• the IP address of a website has the name abc.google.co.uk

These records are “authoritative” because the person who owns the server claims that they are correct in the global naming system, and is providing a content DNS service to provide these answers to anybody who asks for them. Content servers are usually authoritative for a fixed set of domains, owned or administered by the person who has set the server up.
If a content server does not itself know the answer to a particular DNS query, it may know that the domain has been delegated to another server, and so may answer with a referral instead. A referral is a hint to the client making the request that it will find the answer from another content server.

Resolving  DNS server

Resolving DNS server’s job is to search for information on behalf of clients, and to return it. A resolving server usually remembers past queries so that if a lot of people ask for the same information, it can return it quickly without having to search for it twice. Hence a resolving server is sometimes known as a “DNS cache”. Most organizations providing internet access to a group of people maintain their own resolving server (s). See why they are necessary part of the internet infrastructure:

•     Resolving a DNS query from scratch can be a complicated procedure, and most internet software like email clients and web browsers does not need to know how to do it. A commonly-used server to do the job means internet applications need only have to deal with issuing a single question and receiving a single answer.
•     Most DNS information does not change most of the time. Hence it makes sense for an organization to setup their personal server which will be able to more quickly return DNS information that is commonly requested by that particular organization.