The Domain Name Service also known as DNS allows you, the users, to translate names
like www.yahoo.com into a number like 216.32.74.52 which is needed for your computer
to communicate over the network. Networks are controlled by gremlins that only use
numbers not names. Thus DNS is very important if you are going to use the network at
all. Most of the time your ISP provides this service, especially if
you are using a modem, cable modem, DSL, etc. If you are in a large corporate setting,
your own company network will provide DNS.
The main tool you need to check that your DNS is working is nslookup which can translate
names to numbers or vice-versa:
[LocalHost]/home/joe:nslookup www.io.com
Server: flure.pair.com
Address: 209.68.1.159
Name: www.io.com
Addresses: 199.170.88.21, 199.170.88.41, 199.170.88.39
Nslookup tells us there are 3 names that go with www.io.com. Large sites like www.io.com
and www.yahoo.com often have many numbers because they maintain several servers to
handle all the requests to their very busy sites. The server ure.pair.com is our DNS
server as seen by our local DNS setup.
DNS can also translate numbers into names:
[LocalHost]/home/joe:nslookup 199.170.88.21
Server: flure.pair.com
Address: 209.68.1.159
Name: www-02.io.com
Address: 199.170.88.21
This was one of the www.io.com sites listed in the rst example. If DNS can't nd your
name, there is little chance you can connect through the internet to it: