20-755: The Internet
	   Homework 1: Introduction to Internet programming

		      Assigned: Friday, July 16.
		    Due: 10:30am, Monday, July 26.


Team members:
(1)
(2)
(3)


************
Introduction
************

The aim of this homework is to teach you some basics of Internet
programming that will help you get started on your project. When
you're finished you'll understand some of the capabilities of DNS and
you'll have written a simple but nonetheless real server that you can
use as a template for your project.

Please make sure that you understand the solutions for all of the
tasks, even if another group member developed the solution.  In
particular you should be able to explain each line of code in your
group's echo server and know how to perform DNS zone transfers, as
these concepts will likely show up on the final.

The homework, which is 20% of your final grade, consists of 5 tasks
totaling 100 points and a 20-point extra credit question. Each group
member will receive the same score. All tasks should be performed on
euro.ecom.

Julio will be holding recitations on Monday and Friday to help you
with the homework tasks. And please don't hesitate to ask either one
of us for help if your group gets stuck.

*******************************
Task 1. Getting started (10 pts)
*******************************

Use Emacs to create a Perl5 program called "printit.pl" that reads each
line of an input ASCII text file from stdin, prepends "<hostname>:" to
each line, and prints the result to stdout. For example, if the file
foo consists of the following two lines:

  abc
  def

then running "printit.pl < foo" on euro.ecom should generate the
following output:

  euro.ecom.cmu.edu:abc
  euro.ecom.cmu.edu:def

Use the "hostname()" function in the standard Sys::Hostname module
to get your own host name. E.g.:

   #!/usr/local/bin/perl5 -w
   use Sys::Hostname;

   $host = hostname() || die "couldn't get hostname: $!";

(The -w option instructs the Perl interpreter to print out
useful warning message. Every Perl script you write should 
include this option.)

Run your printit.pl program on euro.ecom and redirect the output
to a file. Paste both the source Perl5 program and its output
on euro.ecom below:

ANSWER: 
Paste the source file here:

Paste the output file here:

*****************************************************************
Task 2. Translating between IP addresses and domain names (10 pts)
****************************************************************

(2a) What is the IP address for kittyhawk.cmcl.cs.cmu.edu?

ANSWER: 

(2b) What is the domain name for 128.2.185.143?

ANSWER:

This task can be performed with nslookup in non-interactive mode.
Refer to the nslookup man page for details by typing "man nslookup"
to the shell.

*****************************************
Task 3. Finding DNS name servers (10 pts)
*****************************************

(3a) What are the four name servers for the cs.cmu.edu domain?  

ANSWER: 

For this task you will need to use nslookup in interactive mode. Use
the "set type=ns" command to tell nslookup that you want information
on name servers.

*************************************************
Task 4. Surveying the CMU CS Internet (30 points)
*************************************************

(4a) How many hosts are in the cs.cmu.edu domain?

ANSWER:

In nslookup interactive mode, use the "server <csnameserver>" command
to tell nslookup to query one of the cs.cmu.edu nameservers that you
identified in Task 3. Then perform a zone transfer using the "ls"
command with the output redirected to a file. Use wc to count the
number of lines in the resulting file.

Warning: For no good reason, when you redirect the output of the
nslookup "ls" command, there must be a space after the ">" character
that redirects the result of your query to a file.  That is, you must
type "ls ... > filename" and not "ls ... >file".

(4b) How many of the domain name from (4a) are INTEL machines?

ANSWER:

For this part you can "grep" the output file from the zone transfer
for the string INTEL and then pipe the results into "wc". See the man
pages for grep and wc for more info.

(4c) How many of the INTEL machines from (4b) are running LINUX or
UNIX?  

ANSWER:

For this part, pipe the output of one grep into another, and then pipe
the output of this grep to "wc", once for LINUX and once for UNIX.

***************************************
Task 5. Writing an echo server (40 pts)
***************************************

The simplest Internet server of all is the echo server. An echo server
waits for a connection request from a client to arrive at some port,
and then echos each input line it receives over that connection back
to the client. Not every Internet host has an echo server, but those
that exist listen on port 7. You can try one out for yourself using
telnet as the client:

   % telnet n2.sp.cs.cmu.edu 7

When you are finished, type "^]" followed by the RETURN (ENTER) key to
get the telnet prompt.  Then type "quit" to get back to the shell.

Your task is to write an echo server on euro.ecom called "echo.pl"
that listens on some port between 11000 and 22000 for TCP connection
requests from clients, creates a connection when a request arrives,
and then echos each input line that arrives on that connection back to
the client. Your server should use the "IO::Socket" module:

   #!/usr/local/bin/perl5 -w
   use IO::Socket;

You can use the "perldoc" command to read about this module. Parts
might be cryptic, so we'll also be covering it in class and
recitation:

   % perldoc IO::Socket > socketdoc.txt

You can test your server using telnet as a client:

   % telnet euro.ecom <yourport>

Notice that the telnet client and the echo server can both be running
on euro.ecom at the same time, which might simplify debugging. Also,
you'll find it very helpful to sprinkle your code with print
statements while you are debugging so you can track the status of your
server. E.g,

   print "awaiting next connection request\n"
   print "received connection request\n";
   print "received $line from client\n";
   print "sent $line to client\n";
   print "client closed connection\n";

Mail me the port number your group is using and I'll post them off the
H1 link so we'll be sure to avoid port collisions.

ANSWER: Paste the source code for your echo server here:


*********************
Extra credit (20 pts)
*********************

How many of the domain names in the cs.cmu.edu domain correspond to
machines that are actually up and running?

ANSWER:


What do your results imply about Internet domain surveys that rely
only on DNS zone transfers?

ANSWER:


*****************
Handin directions
*****************

Fill in a copy of this ASCII text file (don't forget to fill in your
team members at the top!) and mail it to droh@cs as a text file (not a
Word document, please) by the due date.

If none of this makes any sense yet, don't panic. We'll be covering
DNS and server design in lecture and recitation Monday. Things will
be much clearer then.

Good luck!