Since we already have working network, we can play with it a bit, can't we?
:)

1. First repeat basic stuff from last exercise -- that is: configuring
   network, test routing (also to the other "network"), whether someone
   replies, who is on the network, ...


2. Have a look on /etc/inetd.conf and find out, which services your computer
   provides, or can provide. Confront its contents with output of program
   "netstat". Find out also, what are the -a, -n, -p parameters of netstat
   for.

3. Except for classical "telnet" service, which you for sure have found in
   inetd.conf, now you want to create a "backup" version of telnet -- telnet
   service, which would run at port 31415. And for convenience, let's call
   this new service "supertelnet". After correct setup we should be able to
   execute "telnet 127.0.0.1 supertelnet" and it should have the desired
   effect.

   Hint: Telnet in telnet isn't neccessary the next best thing since sliced
   bread. CTRL+] and then command "set escape ^^" might help.

   Hint #2: Of course, previous hint almost calls for further explanation.
   :-)

4. Have a look at files /etc/hosts.allow and /etc/hosts.deny. Do you have
   any idea what they are for and what is their format? Could you assure
   that the new "supertelnet" service would be accessible only for one
   computer and not for all?

5. Since you already have supertelnet (or also normal telnet), you can enjoy
   jumping from one computer to another back and forth or trying to defend
   against each other. :-)