What are some simple ways to test IP communications? Most readily available are
lsof lists open filedescriptors for both Unix files and sockets. This is particularly handy for tracking down which processes occupy which ports.
Sources for Stevens and Comer's Internetworking with TCP/IP, volume III (BSD) are freely available.
Highly recommended: the Unix-socket-faq.
This is a Perl script which reads and lightly massages ARP tables. One way to look at it is as a table of MAC addresses sorted by IP address.
Simple Sockets Library
Xvfb [X Virtual Frame Buffer] is a dummy-load for X-servers, an X-server with no display.
I'm frequently called on to explain TIME_WAIT. I'll describe what I know here, in time. Note that HP-UX has a command-line option to release, and Solaris has the tcp_close_wait_interval kernel parameter, whose default is 240000 (milliseconds).