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CS514: Homework 3
CS514: Homework 3
Collaboration.
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 and
the solution should list the names of the collaborators.
Other collaborations will be considered violations of Academic Integrity.
Submission Procedure.
Solutions must be submitted by email to:
cs514@cs.cornell.edu
The solution may by formatted as ASCII (i.e. plain text) or postscript.
Due Date.
We must receive your email by 8:00(am) on Wed., April 3, 1996.
Late Assignments will not be accepted.
Problem Description
Read RFC 821, The Simple Mail Transfer Protocol, and RFC 822,
Standard for the Format of ARPA-Internet Text Messages. RFCs can be
retrieved from rs.internic.net using anonymous ftp. A selection
of the RFCs is available at the departemental machines in the directory
/vol/doc/InterNet.
-
Find out what a domain literal 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 here for additional hints concerning this part of the
assignment.
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Excluding the connection establisment and termination, what is the
minimum number of network round trips to send a small mail message?
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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 write
that contains the HELO, MAIL, RCPT, DATA and QUIT commands
(assuming the body isn't too large)?
-
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 implement
a load balancing scheme for incoming electronic mail?
This assignment requires using ftp to connect to machines outside the CS
Department firewall.
There are two options for this:
- Use ncftp, a new interface to the ftp client. It automatically
starts a connection in anonymous user mode, so that you do not have to
type user names and mail addresses. It also requests that the peer machine
use passive mode when transfering data, thereby allowing data to flow back
over the already established TCP connection (and avoiding problems
with the firewall).
-
If the remote ftp server does not support passive mode (something indicated
if you do not get any response to a "dir" or "get" request) you will
have to resort to the second option.
Use ftp 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 not type in your own password but instead type your
e-mail address.
More information can be found in the tips-firewall manual page.