Page 116 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Network Operating Systems-I

notes When you want to browse to www.their-domain.com your DNS server (the one you state in the
TCP/IP configuration on your desktop computer) most likely won’t have a DNS record for the
their-domain.com domain so it has to contact the DNS server that does. When your DNS server
contacts the DNS server that has the DNS records (referred to as “resource records” or “zone
records”) for their-domain.com your DNS server gets the IP address of the www server and
relays that address back to your desktop computer. So which DNS server has the DNS records
for a particular domain?
When you register a domain name with somebody like Network Solutions, one of the things they
ask you for are the server names and addresses of two or three “name servers” (DNS servers).
These are the servers where the DNS records for your domain will be stored (and queried by the
DNS servers of those browsing to your site). Typically, when you host your Web site using a Web
hosting service they not only provide a Web server for your domain’s Web site files but they will
also provide a DNS server to store your domain’s DNS records. In other words, you’ll want to
know who your Web hosting provider is going to be before you register a domain name (so you
can enter the provider’s DNS server information in the name servers section of the domain name
registration application). Once you’ve got your Web site up and running on your Web hosting
provider’s servers and someone surf’s to your site, the DNS server they specified in their local
TCP/IP configuration will query your hosting provider’s DNS servers to get the IP address for
your Web site. The DNS servers that host the DNS records for your domain, i.e. the DNS servers
you specify in your domain name registration request, are the authoritative DNS servers for
your domain. The surfer’s DNS server queries one of your site’s authoritative DNS servers to get
an address and gets an authoritative response. When the surfer’s DNS server relays the address
information back to the surfer’s local PC it is a “non-authoritaive” response because the surfer’s
DNS server is not an authoritative DNS server for your domain.

Example: If you surf to MIT’s Web site the DNS server you have specified in your TCP/IP
configuration queries one of MIT’s reliable DNS servers and gets an authoritative response with
the IP address for the ‘www’ server. Your DNS server then sends a non-authoritative response
back to your PC. You can easily see this for yourself. At a shell prompt, or a DOS window on a
newer Windows system, type in:

nslookup www.mit.edu
First you’ll observe the name and IP address of your locally-specified DNS server. Then you’ll see
the non-authoritative response your DNS server sent back containing the name and IP address
of the MIT Web server.
If you’re on a Linux system you can also notice which name server(s) your DNS server contacted
to get the IP address. At a shell prompt type in:

whois mit.edu
and you’ll see three authoritative name servers listed with the hostnames STRAWB, W20NS, and
BITSY. The ‘whois’ command only returns the contents of a site’s domain record.

Did u know? So where do you get the “name servers” information for your domain?

Don’t puzzle DNS zone records with domain records. Your domain record is created when you
fill out a domain name registration application and is maintained by the domain registration
service (like Network Solutions) you used to register the domain name. A domain only has one
domain record and it contains administrative and technical contact information as well as entries
for the authoritative DNS servers (aka “name servers”) that are hosting the DNS records for
the domain. You have to enter the hostnames and addresses for multiple DNS servers in your
domain record for redundancy (fail-over) purposes.

110 LoveLy professionaL university