What happens when you type "www.google.com" in your browser, and press Enter?

• We need to translate the name of site "www.google.com" to an IP address.

IP address identifies a server or a computer on the internet. It is simply a number in this form: w.x.y.x. Each number can range from 0-255 and we need 8 bits to represent this number. IP address contains 4 such numbers, so 32 bits are required to represent an IP address.

• To convert website names to IP address, the computer has to do a domain name lookup using a DNS (Domain Name System). DNS is an infrastructure on the internet that converts domain names / host names to IP addresses and vice versa. It also does few other things, like email routing, validation of domain ownership.

Your computer does not have its own DNS server. But, your internet provider like Comcast, Verizon or your company or your university campus has got their own DNS servers.

• There is a hierarchy to the DNS system. If your type "www.9gag.com" and company's DNS server has no idea about it (since its not in company's DNS database), your company's DNS server can ask to its ISP's (E.g. Comcast) DNS server abput this host name's address. Your ISP has got bigger database of websites than your company's DNS server. If your ISP even does not have an idea about this website, then it looks up to root DNS servers.

Even though you might have your own DNS server in your campus or in your company, it doesn't necessarily all possible domain names and IP addresses in the world. That would be quite a large database otherwise and its not efficient to keep them all if they are not used very frequently.

Root DNS servers are spread out geographically across the several continents and they essentially know SOMEBODY WHO DOES know what the IP address of some random website is. Root servers know who the authority is for all the .com domains in the world, or .net domains in the world.