Reti di Computer - DNS - Computers Networks

Every web site has a name, of course, like for instance, www.google.it and so on. Its files are on a server that is a computer in some part of the world. So when we write a domain name (www.google.it) in the address line of our browser, ( the URL line ) we can see the web site we were looking for.

But computers do not work with real names but with numbers only. So there must be a way to let them understand what we are writing in our browser.

DNS - Domain Name Service - is a system which translates a domain name into numbers.

The web site www.google.it is translated into 216.239.39.104. In fact if we write this numbers in the address line of our browser, we are redirected the web site google.it

This numbers are the IP - Internet Protocol - address.

Any computer connected to the Internet has a unique IP address, in the form of XXX.XXX.XXX.XXX, where XXX is an integer between 1 and 255. This number identifies the computer and the network to which it is connected.

There are a lot of computers all around the world acting as DNS servers which have large databases of IP addresses corresponding to domain names. The whole Internet is divided in zones with a DNS server.

Root Name Server:
A: There are 12 operators for root DNS at 13 unique IP addresses.
A - VeriSign Naming and Directory Services
B - Information Sciences Institute (University of Southern California)
C - Cogent Communications
D - University of Maryland
E - NASA Ames Research Center
F - Internet Systems Consortium, Inc.
G - U.S. DOD Network Information Center
H - U.S. Army Research Lab
I - Autonomica
J - VeriSign Naming and Directory Services
K - RIPE NCC (Reseaux IP Europeens - Network Coordination Centre)
L - ICANN (Internet Corporation for Assigned Names and Numbers)
M - WIDE Project

Each letter from A to M identifies a single IP address. They are situated in more than 35 countries ( more than 84 locations ), most of them outside the USA. Not all the exact locations of the root servers are known because of security reasons.

This is how it works:

We want to go to www.symantec.com

1)Our computer asks our ISP ( Internet Service Provider - that is the company which provides us the Internet connection ) DNS server what is the number (IP) of this web site. If this server knows it, our computer will be connected with the computer where this site is.

2)If our ISP DNS server has not that information,it will ask other DNS servers until it finds the IP number which it is looking for. After that, our computer will be connected with the computer where this site is.

3)If it is not possible to find that address - wrong number or the web site does not exist - our browser will not be able to show us that web site.

DNS propagation: it is the process which inserts a website IP number into the DNS server around the world. It may take up to 72 hours. This is why a new website is not visible on the Internet before that period of time.

Renato Piccini - Florence - Italy Computers Networks technician - http://www.softgrafic.com

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