Page 114 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Network Operating Systems-I

notes In addition, you can insert more entries in the named.conf file to reference other Web domains
you host. Here is an case for another-site.com using a zone file named another-site.zone.
zone “another-site.com” {
type master;
notify no;
allow-query { any; };
file “another-site.zone”;

};
6.1.2 Dns server

As a service, DNS is crucial to the operation of the Internet. When you enter www.some-domain.
com in a Web browser, it’s DNS that takes the www host name and translates it to an IP address.
Without DNS, you could be connected to the Internet just fine, but you ain’t goin’ no where. Not
unless you keep a record of the IP addresses of all of the resources you access on the Internet and
use those instead of host/domain names.
So when you visit a Web site, you are in fact doing so using the site’s IP address even though
you specified a host and domain name in the URL. In the background your computer quickly
queried a DNS server to get the IP address that corresponds to the Web site’s server and domain
names. Now you know why you have to specify one or two DNS server IP addresses in the TCP/
IP configuration on your desktop PC (in the resolv.conf file on a Linux system and the TCP/IP
properties in the Network Control Panel on Windows systems).

A “cannot connect” error doesn’t essentially indicate there isn’t a connection to the destination
server. There may very well be. The error may indicate a failure in “resolving” the domain
name to an IP address. I use the open source Firefox Web browser on Windows systems because
the status bar gives more informational messages like “Resolving host”, “Connecting to”, and
“Transferring data” rather than just the generic “Opening page” with IE. (It also seems to render
pages faster than IE.)
In short, always check for right DNS operation when troubleshooting a problem involving the
inability to access an Internet resource. The ability to resolve names is critical, and later in this
page we’ll show you some tools you can use to investigate and verify this capability.
When you are surfing the Web viewing Web pages or sending an e-mail your workstation is
sending queries to a DNS server to determine server/domain names. (Back on the Modems page
we showed you how to set up your resolv.conf file to do this.) When you have you own Web site
that other people visit you need a DNS server to respond to the queries from their workstations.
When you visit Web sites, the DNS server your workstation question for name resolution is
typically run by your ISP, but you could have one of your own. When you have your own Web
site the DNS servers which respond to visitors queries are typically run by your Web hosting
provider, but you could likewise have your own one of these too. Actually, if you set up your
own DNS server it could be used to respond to both “internal” (from your workstation) and
“external” (from your Web site’s visitors) queries.

Even if you don’t have your own domain name, or even your own LAN, you can still have
advantage from using a DNS server to allow others to access your Debian system. If you have
a single system connected to the Interent via a cable or DSL connection, you can have it act as
a Web/e-mail/FTP server using a neat service called “dynamic DNS” which we’ll cover later.
Dynamic DNS will even work with a modem if you want to play around with it.

108 LoveLy professionaL university