Computer Networks Practical #10

Computer Networks

The nslookup and dig Unix command-line utilities allow humans to look up RRs in the DNS. They work in rather different ways, with nslookup being oriented towards an interactive user interface, whilst dig wants all of its arguments on the command line. However, dig is better in that it shows all of the RRs returned from the DNS, whereas nslookup only gives you the answer to your question. You can also ask dig to return any RRs associated with a particular domain name. Note that there are software tools with similar functionality for both PCs and Macs.
Use these utilities to investigate the DNS. Within nslookup, type h for help and take it from there. Try typing bindi.bendigo.latrobe.edu.au and bindi.bendigo.latrobe.edu.au. (ie, with a trailing dot). Try just bindi on its own, and bindi.bendigo Interesting? Try set query=CNAME, or a few other RR types, then repeat the exercise. Try a PTR lookup - how do each of the utilities handle these? What about an SOA? NB: use exit or ^D to quit from nslookup.
Ever thought of registering your own domain name? It's not so difficult. In Australia, check out AUNIC. It has links to just about everything you could want to know about Internet domain names.

Here's a definitive guide to DNS.
There are several good DNS tutorials available on the Web. Try, for example, a "goeureka" search for "domain name system" DNS tutorial. You also get a few good hits at google.com. Two of the best DNS tutorials I've found are http://www4.ulpgc.es/tutoriales/tcpip/pru/3376c45.htm and http://www.seas.upenn.edu/~ross/book/apps/dns.htm. Very extensive and well worth a look. Telstra BigPond Direct has a good explanation of the various RR types in the DNS. Here's the bare bones of another lecture on DNS, with something of a Linux emphasis. This one is not bad either.

This set of practical exercises accompanies Tutorial #10.
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