Submission Instructions Please submit your homework solutions by EMAIL to me at Russ.Clark@gatech.edu. Make sure to include [CS3251] in subject line.

Late Policy: You have a total of 3-days for a late budget which you may use for any assignment in a minimum of one day increments.

1. Question 1: DNS

   Use the nslookup command to answer the following questions. You can find nslookup on most any Solaris or Linux system. If you aren't sure where to look, try /usr/sbin/nslookup on acme.

   1. What is the IP address of the authoritative name server for the domains: gatech.edu, cnn.com, whitehouse.gov

      gatech.edu IP address = 130.207.244.244
      cnn.com IP Address: 64.236.16.20, 64.236.16.52, 64.236.24.12, 64.236.29.120, 64.236.91.21, 64.236.91.22, 64.236.91.23, 64.236.91.24
      whitehouse.gov IP address = 63.161.169.137
      

   2. What are the IP addresses returned for the hosts: www.gatech.edu, www.cnn.com, www.whitehouse.gov

      www.gatech.edu          A       130.207.165.120
      
      www.cnn.com             A       64.236.91.21
      www.cnn.com             A       64.236.91.22
      www.cnn.com             A       64.236.91.23
      www.cnn.com             A       64.236.91.24
      www.cnn.com             A       64.236.16.20
      www.cnn.com             A       64.236.16.52
      www.cnn.com             A       64.236.24.12
      www.cnn.com             A       64.236.29.120
      
      www.whitehouse.gov      CNAME   www.whitehouse.gov.edgesuite.net
      www.whitehouse.gov.edgesuite.net        CNAME   a1289.g.akamai.net
      a1289.g.akamai.net      A       143.215.203.7
      a1289.g.akamai.net      A       143.215.203.17
      

      (Try these requests several times. Note the addresses returned in different queries. Explain what is happening.)

      The order of the cnn.com addresses tend to change frequently, probably for load balancing.
      

   3. Use the MX record to find the mail server for these three domains: gatech.edu, cnn.com, whitehouse.gov

      gatech.edu              MX      mx4.gatech.edu
      gatech.edu              MX      mx5.gatech.edu
      gatech.edu              MX      mx1.gatech.edu
      gatech.edu              MX      mx2.gatech.edu
      gatech.edu              MX      mx3.gatech.edu
      
      cnn.com                 MX      atlmail3.turner.com
      cnn.com                 MX      atlmail5.turner.com
      cnn.com                 MX      nycmail1.turner.com
      cnn.com                 MX      nycmail2.turner.com
      cnn.com                 MX      lonmail1.turner.com
      cnn.com                 MX      hkgmail1.turner.com
      
      whitehouse.gov          MX      mailhub-wh2.whitehouse.gov
      whitehouse.gov          MX      mailhub-wh3.whitehouse.gov
      
      

2. Question 2: HTTP

   Review RFC 2616, the HTTP/1.1 specification. Explain the mechanism used for signaling between the client and server to indicate that a persistent connection is being closed. Can the client, the server, or both signal the close of the connection?

   Both the client and server have the ability to close a connection.
   When either the client or server wishes to close the connection then it
   sends a connection header including the "close" connection-token. 
   A request which includes this token becomes the last request for that connection.
   

3. Question 3: Mail
   1. Create a sample email message as it might appear from a user at gmail.com to another user at gatech.edu. Give the relevant fields and format of the message.

      Return-Path:	<GMUser@gmail.com>
      Date:		Sun, 22, Apr 2007 17:02:31 -0700 (PDT)
      From:		"GMail User" <GMUser@gmail.com>
      Reply-To:	GMUser@gmail.com
      To:		George.Burdell@mail.gatech.edu
      Subject:	Graduation is Coming
      
      Hey George! Have you ordered your cap and gown yet?
      
      GM
      

   2. Give the SMTP message flow diagram for the sender delivering this message to the destination mailbox.

      Gatech:		220 gatech.edu
      Gmail:		HELO gmail.com
      Gatech:		250 Hello gmail.com, pleased to meet you
      Gmail:		MAIL FROM: <GMuser@gmail.com>
      Gatech:		250 Sender ok
      Gmail:		RCPT TO:  <George.Burdell@mail.gatech.edu>
      Gatech:		250 Recipient ok
      Gmail:		DATA
      Gatech:		354 End data with <CR><LF>.<CR><LF>
      Gmail:		[exact content of message in previous answer]
      Gmail:		.
      Gatech:		250 Message accepted for delivery
      Gmail:		QUIT
      Gatech:		221 Bye
      

   3. Give the POP3 message flow diagram for the recipient retrieving the message from the mailbox.

      Server:	 +OK POP3 server ready
      Client:	  user gburdell
      S:	 +OK
      C:	 pass stillhere
      S:	 +OK user successfully logged in
      C:	 list
      S:	 1 214
      S:	 .
      C:	 retr 1
      S:	 [exact content of message in previous answer]
      S:	 .
      C:	 dele 1
      C:	 quit
      S:	 +OK POP3 server signing off