INT20CN Computer Networks

Practical Exercises #4

1. Use netscape (or InternetExplorer, or even lynx) to fetch an RFC -- RFC854 (telnet) might be a good one. You can do this by clicking on the URL given in the first slide of the lecture.

2. One of the annoying little aspects of computer programming is that occasionally a programmer has to look up the ASCII value of a character, but can't find an "ASCII chart". One of the standard Unix "Tricks of the Masters" is that you can always type man ascii at the command line. Try it.

3. Look at the file /etc/services on a nearby Unix system: it defines the mapping between TCP port numbers and application protocols. Find the port numbers for echo, finger and chargen. Use telnet to connect to each of these ports. What do they do? Note that on some systems the telnet program accepts symbolic, or service, names on the command line. You might care to try it, eg:

   telnet ironbark.bendigo.latrobe.edu.au finger
   

4. Try using rlogin from one of the campus Unix systems to another Unix system. Do you notice any difference between the way it operates, compared to telnet?

5. Try using ssh to to log in from one of the Unix systems to another on campus. Any difference?

6. Use a text editor on a PC (eg, NotePad) or Mac (eg SimpleText) to create a text file. Then transfer the text file to a Unix system (or some other dissimilar system) -- how you do this is up to you, but using a floppy disk is probably your best option. Then open the file using a Unix text editor (eg, vi or nedit). What do you observe?

7. Try^[1] using telnet to connect to another machine, say A, then invoke it on A to reach yet another machine, call it B. You could do this between any two of the Unix systems in the Unix lab. How does the combination of two telnets work? Any problems? What happens when you type the Escape character? Are <CR> (carriage return) and <LF> (line feed) characters handled properly?