Network Administration: DNS Operations - dummies

Network Administration: DNS Operations

With the nslookup command in your trusty TCP/IP toolbox, take a little trip through the Internet’s maze of DNS servers to find out how DNS gets from www.disneyland.com to an IP address in just a matter of milliseconds.

DNS does its whole name resolution thing so fast, it’s easy to take it for granted. If you follow this little procedure, you’ll gain a deeper appreciation for what DNS does literally tens of thousands of times every second of every day.

  1. At a command prompt, type nslookup without any parameters.

    nslookup displays the name of the default name server and displays the > prompt.

    C:>nslookup
    Default Server:  ns1.orng.twtelecom.net
    Address:  168.215.210.50
    >
  2. Type root to switch to one of the Internet’s root servers.

    nslookup switches to one of the Internet’s 13 root servers and then displays the > prompt.

    > root
    Default Server:  A.ROOT-SERVERS.NET
    Address:  198.41.0.4
  3. Type www.disneyland.com.

    nslookup sends a query to the root server to ask if it knows the IP address of www.disneyland.com. The root server answers with a referral, meaning that it doesn’t know about www.disneyland.com, but you should try one of these servers because they know all about the com domain.

    > www.disneyland.com
    Server:  A.ROOT-SERVERS.NET
    Address:  198.41.0.4
    Name:    www.disneyland.com
    Served by:
    - A.GTLD-SERVERS.NET
              192.5.6.30
              com
    - G.GTLD-SERVERS.NET
              192.42.93.30
              com
    - H.GTLD-SERVERS.NET
              192.54.112.30
              com
    - C.GTLD-SERVERS.NET
              192.26.92.30
              com
    - I.GTLD-SERVERS.NET
              192.43.172.30
              com
    - B.GTLD-SERVERS.NET
              192.33.14.30
              com
    - D.GTLD-SERVERS.NET
              192.31.80.30
              com
    - L.GTLD-SERVERS.NET
              192.41.162.30
              com
    - F.GTLD-SERVERS.NET
              192.35.51.30
              com
    - J.GTLD-SERVERS.NET
              192.48.79.30
              com
    >
  4. Type server followed by the name or IP address of one of the com domain name servers.

    It doesn’t really matter which one you pick. nslookup switches to that server. (The server may spit out some other information besides what’s shown here)

    > server 192.48.79.30
    Default Server:  [192.5.6.30]
    Address:  192.5.6.30
    >
  5. Type www.disneyland.com again.

    nslookup sends a query to the com server to ask whether it knows where the Magic Kingdom is. The com server’s reply indicates that it doesn’t know where www.disneyland.com is, but it does know which server is responsible for disneyland.com.

    Server:  [192.5.6.30]
    Address:  192.5.6.30
    Name:    www.disney.com
    Served by:
    - huey.disney.com
              204.128.192.10
              disney.com
    - huey11.disney.com
              208.246.35.40
              disney.com 
    >

    Doesn’t it figure that Disney’s name server is huey.disney.com? There’s probably also a dewey.disney.com and a louie.disney.com.

  6. Type server followed by the name or IP address of the second-level domain name server.

    nslookup switches to that server:

    > server huey.disney.com
    Default Server:  huey.disney.com
    Address:  204.128.192.10
    > 
  7. Type www.disneyland.com again.

    Once again, nslookup sends a query to the name server to find out whether it knows where the Magic Kingdom is. Of course, huey.disney.com does know, so it tells us the answer:

    > www.disneyland.com
    Server:  huey.disney.com
    Address:  204.128.192.10
    Name:    disneyland.com
    Address:  199.181.132.250
    Aliases:  www.disneyland.com
    > 
  8. Type Exit, and then shout like Tigger in amazement at how DNS queries work.

    And be glad that your DNS resolver and primary name server do all this querying for you automatically.

Okay, maybe that wasn’t an E Ticket ride, but it never ceases to amaze me that the DNS system can look up any DNS name hosted anywhere in the world almost instantly.