CSC 102

Lab: NSLookup

 

DOS Command Window

See Ping Lab for how to open a window for DOS commands. Recall that you can interrupt a command that is taking too long by pressing CTRL-C.

nslookup

  1. We will directly query the local DNS, using the command nslookup, which has an exact Unix/MacOSX equivalent. It is executed like this: 

    > nslookup -d sophia.smith.edu

    (Don't type the >; that is just to show you the DOS prompt.) This returns a heap of information (because we specified the "-d" option, which means "give me the details)," most of which we have no particular use for. You will see in the pile of information, the name of our DNS server: babel.smith.edu. Look to see if you can find that. Also look for the word "authority," which is indicating that this DNS server is the authority on that domain name, and Smith's own DNS server is the authority on the Smith hosts.

  2. All but network engineers use nslookup in the non-detail form:

    > nslookup sophia.smith.edu

    and this is what we will use exclusively. This should show you an output something like this:

    Server: babel.smith.edu
Address: 131.229.64.2
  
Name: sophia.smith.edu
Address: 131.229.64.1

    This is how to read this. Your request is being handled by the DNS whose domain name is babel.smith.edu and IP address 131.229.64.2. The domain name you looked up is sophia.smith.edu and its IP address is 131.229.64.1.

  3. Try some local hosts. (You might copy from a Web page [Edit/Copy or the copy icon] and paste into the DOS window [right-click/Paste].) 

    aurora.smith.edu
sophia.smith.edu
cs.smith.edu
math.smith.edu
cs.umass.edu

    Note that some domain names are aliases for others, and it will show you the primary domain name.

    Try to guess from the IP addresses for Smith machines: what all IP address at Smith look like, i.e., what pattern of numbers is shared by Smith IP addresses.

  4. Try the nslookup command in reverse: Put in an IP address, and get back the domain name: 

    > nslookup 131.229.64.1
    • Try an IP address that you know is correct, i.e., one of the ones returned above.
    • Make up an IP address, keeping the legal structure correct (four numbers, each at most 255, separated by dots), and see what you get. Quite likely you'll get a "Host not found" message.
    • Try an address which is just one more in the fourth (rightmost) number for an address that you know works. This might find another legal host.
  5. Now try some more remote hosts: 
    cs.berkeley.edu
microsoft.com
www.gcal.ac.uk
www.sfi.ie
iprimus.com.au
mousse.ens.fr

    Or try any of the hosts from the ping Lab that worked.

  6. Link to one of these sites to find out where those last four hosts (in the list above) are.

    Remember that you can revisit any of these links to determine the meaning of any country code you encounter.