Intermediate Systems Administration DeCal
Week 7 Lab
=========================================

    This week we talked about the wonderful world of Internet services such as
HTTP, DHCP, DNS, and SMTP. This lab is just a continuation of the overview I
gave in class - it's very important to understand what the services are that
power your "Internet experience." If you do sysadmin work one day, chances are
you will be asked to administer at least one of these kinds of servers.
    This lab has a shell script to write (oh noes!) so do take a look at that
carefully.
    I'll also be looking at your project proposals, so watch your inboxes
throughout the course of the week in case I need to discuss it with your group.
Once I've acked your proposal you should begin working on it.
    Answers go to joshk.decal@triplehelix.org as usual.

I. Interacting with Mail Locally
--------------------------------
	In this exercise we'll poke around with the most common mail-oriented commands in the Unix world, using the institutional machines.

1. Use the 'mail' command to send yourself a message. How do you specify a
subject? How do you read your mail using this command?

2. Play around with mutt and pine and figure out how to send and browse email
messages in both. Which do you prefer, and why? (The mail client war is about
40% more intense than the editor war.)

3. Try using sendmail -t or sendmail -bs (what's the difference?) to manually
send a message to someone. If you are comfortable with SMTP, sendmail -bs will
be easier. Provide a transcript of your session.

II. DNS queries
---------------

    You should do this on your virtual server. Please install the host package
as well as the dnsutils package.

1. Use host to look up the MX record for berkeley.edu, show the syntax you used.

2. One kind of record I didn't talk about during the lecture is the NS record.
   Use google to figure out what the NS record is and find the NS record for
   berkeley.edu. To the best of your knowledge, where are all the DNS servers
   listed in the NS record located? Is it a good thing that they're spread out?
   Think of a reason why that's good.

3. Use dig to perform the queries from above and show the syntax you used.
   Now, just type 'dig' by itself. What do you see in the "ANSWER SECTION"?
   What are these servers? Google may help.

III. HTTP
---------

Please install the netcat package on your virtual server before trying this.

1. Write a shell script that behaves like wget for a single URL. Here's what
   your script should do, step by step.
- Assume the URL is in the format "http://www.xxxxxxx.com/abcd1234". Don't
  worry about escapes and special characters.
- Use cut to extract "www.xxxxxxx.com" as the server name, and "/abcd1234"
  as the path. Remember that the path may contain an arbitrary number of
  slashes so you need to pass the right option to cut to fetch the entire string
  after the index you specify. (Email me for clarification about this.)
- Now, use netcat to connect to port 80 of the server. netcat accepts input
  that you pipe into it. Remember that an HTTP request looks like:
  "GET /path/x/y/z HTTP/1.0" followed by TWO NEWLINES. We will use a syntax
  for echo that you haven't learned about yet:

  echo -e "GET /path/x/y/z HTTP/1.0\n\n"

  The -e specifies that your input string contains escapes (in this case, the
  \n.) Thus, your connection recipe should look like this:

  echo -e "(the request) | nc $SERVER 80
- Pipe this input into a read loop (like you used for tv-rename). Discard lines
  until you see a line with only a new line. This specifies the end of the HTTP
  header. You can use [ "$line" = $'\r' ] to test for this (copy and paste.)
  After the blank line, echo the lines back out thereafter.
- The loop itself should be redirected into a file called 'output'.

In summary, here's a pseudocode - I feel this is difficult, so I've provided
the entire structure of the loop. Of course, this is pseudocode, so you must
still fill in the blanks for it to work.

set SERVER from input string
set PATH from input string

set BLANK_LINE_SEEN to 0
echo -e "the http request" | nc SERVER 80 | while read line; do
    if BLANK_LINE_SEEN is 1
        echo the line
    elif the line = $'\r'
        set BLANK_LINE_SEEN to 1
done > output

Remember to try the nc interaction yourself on the command line first so
you can understand what is going on. Also try the echo -e stuff on its own
so you can see what happens. Finally, use sh -x with your script to debug it.