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<HEAD><TITLE>CS514: Homework 3</TITLE></HEAD><BODY><H2>CS514: Homework 3</H2><b>Collaboration</b>.Collaboration by up to three students is permitted on this assignment.When there is such a collaboration, a single solution should be submitted for grading andthe solution should list the names of the collaborators.Other collaborations will be considered violations of Academic Integrity.<P><b>Submission Procedure</b>.Solutions must be submitted by email to:<PRE> cs514@cs.cornell.edu</PRE>The solution may by formatted as ASCII (i.e. plain text) or postscript.<P><b>Due Date</b>.We must receive your email by 8:00(am) on <b>Wed., April 3, 1996</b>.Late Assignments will not be accepted.<H2>Problem Description </H2>Read RFC 821, <I>The Simple Mail Transfer Protocol</I>, and RFC 822, <I>Standard for the Format of ARPA-Internet Text Messages</I>. RFCs can beretrieved from <B>rs.internic.net</B> using anonymous ftp. A selectionof the RFCs is available at the departemental machines in the directory<I>/vol/doc/InterNet</I>.<P><OL><LI> Find out what a <I>domain literal</I> is from RFC 822. Try sending a mail message to yourself using one.Include a copy of the message you received in your homework solution.Click <A HREF="hw.03.news.html">here</A> for additional hints concerning this part of theassignment.<P> <LI>Excluding the connection establisment and termination, what is theminimum number of network round trips to send a small mail message?<P> <LI>TCP is a full-duplex protocol, yet SMTP uses TCP in a half-duplex fashion. The client sends a command then stops and waits for the reply.Why doesn't the client send multiple commands at once--for example, a single writethat contains the HELO, MAIL, RCPT, DATA and QUIT commands(assuming the body isn't too large)?<P> <LI>Consider an organization that is serviced by a collection of mail transfer agents.How can the DNS MX records and preference values be used to implementa load balancing scheme for incoming electronic mail?</OL><P>This assignment requires using ftp to connect to machines outside the CSDepartment firewall.There are two options for this:<UL><LI> Use <I>ncftp</I>, a new interface to the ftp client. It automaticallystarts a connection in anonymous user mode, so that you do not have totype user names and mail addresses. It also requests that the peer machineuse <I>passive</I> mode when transfering data, thereby allowing data to flow back over the already established TCP connection (and avoiding problemswith the firewall).<P><LI> If the remote ftp server does not support passive mode (something indicatedif you do not get any response to a "dir" or "get" request) you willhave to resort to the second option.Use <I>ftp</I> to connect to the firewall machine (fw.cs.cornell.edu).When the program asks for a user name, respond with "anonymous@remote.machine" but replacing remote.machine with the name of the machine you want to reach. The firewall proxy server will then setup a control connection and manage any future incoming data connections for your. When a password is asked, do <B>not</B> type in your own password but instead type your e-mail address.</UL>More information can be found in the <I>tips-firewall</I> manual page.</BODY>⌨️ 快捷键说明
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