1. Introduction to DNS

The fact is we are very comfortable using and remembering the names instead of numbers. Moreover, these IP address changes over time and some of the sites have multiple IP addresses. Also, the transfer of data over the internet is only possible using IP addresses because the routing of the packet of data sent over the internet is done using IP address.

There is a server called Domain Name System (DNS) which takes care of these translation jobs to simplify and to save us from remembering these changing IP addresses, the DNS. Whenever you type an address like www.google.com, there is a process called DNS name resolution, that takes place in the background.

The computer keeps track of recently visited sites and locally maintains a database in DNS cache. In case, the IP address of the site you have requested is not found in the DNS cache of your local computer, then the next probable place to find it is the DNS server of your Internet Service Provider (ISP).

2. Root Name Servers

These DNS servers of ISPs also maintain the cache of the recently visited pages. Just in case, the information is not found here also, the DNS server of the ISP forwards the query to the root nameservers. The root name servers publish the root zone file to other DNS servers and clients on the Internet. The root zone file describes where the authoritative servers for the DNS top-level domains (TLD) are located. There are currently 13 rootname servers. They are;

1. A - VeriSign Global Registry Services
2. B - University of Southern California - Information Sciences Institute
3. C - Cogent Communications
4. D - University of Maryland
5. E - NASA Ames Research Center
6. F - Internet Systems Consortium, Inc.
7. G - U.S. DOD Network Information Center
8. H - U.S. Army Research Lab
9. I - Autonomica/NORDUnet
10. J - VeriSign Global Registry Services
11. K - RIPE NCC
12. L - ICANN
13. M - WIDE Project

These root nameservers direct the query to the appropriate Top-Level Domain (TLD) nameservers by reading the last part of the URL first. In our example, the URL was www.google.com. The last part is .com. Some of the examples of TLD name servers are;

• .com
• .biz
• .in
• .net
• .co
• .online
• .co.in
• .org, etc

These TLD nameservers act as a switchboard and direct the query to the appropriate authoritative nameserver maintained by each domain. This authoritative nameserver maintains DNS records along with other useful information. This address record is returned to the requesting host computer via TLD nameservers, nameservers, and ISP's DNS server. This intermediary server keeps the recond of this IP address in their DNS cache so that if the same request is encountered again, they don't have to go through this process again. If the same URL is requested again, the DNS cache of the local host computer will return the IP address of the URL.