feb 9
Questions?
Review :
- What's TCP/IP ?
- What's a port ?
- What's an "application layer protocol?"
- What a "client/server" protocol?
- Give some examples.
Today:
- Discuss other application protocols : email, bittorrent
- (Homework due Thurs is all related to email.)
- ... but first discuss ports.
ports
There are *lots* of application protocols;
here's a list. Note that some well known ones
(like bittorrent) aren't even "registered."
Daytime protocol example :
thirty$ telnet time-nw.nist.gov 13
Trying 131.107.13.100...
Connected to time-nw.nist.gov.
Escape character is '^]'.
55236 10-02-09 00:24:50 00 0 0 748.3 UTC(NIST) *
Connection closed by foreign host.
port scanning
Sending something to each port to try to figure out what's running on a given computer is called "port scanning."
This is a common security audit (if you're a good guy) or
the beginning of a network intrusion (if you're a bad guy).
thirty$ nmap zonorus.marlboro.edu
Starting Nmap 5.00 ( http://nmap.org ) at 2010-02-08 19:12 EST
Interesting ports on zonorus.marlboro.edu (216.158.162.3):
Not shown: 991 filtered ports
PORT STATE SERVICE
20/tcp closed ftp-data
21/tcp open ftp
22/tcp open ssh
25/tcp open smtp
80/tcp open http
110/tcp open pop3
143/tcp open imap
993/tcp open imaps
995/tcp open pop3s
email
One of the oldest, most prevalent, and problematic internet services is email. It's implemented via a number of protocols these days.
SMTP
POP3
- wikipedia:post office protocol, version 3
- for reading mail
- IMAP (internet message access protocol) is another one.
- port 110 (negotiated encryption)
- port 995 (SSL encryption)
The wikipedia pages give a sample dialog;
I may try this in class ... but it's hard to hide the passwords.
$ telnet mail.marlboro.edu 110
Connected to akbar.marlboro.edu.
Escape character is '^]'.
+OK Dovecot ready.
USER mahoney
+OK
PASS *****
+OK Logged in.
LIST
+OK 0 messages:
.
QUIT
+OK Logging out.
Connection closed by foreign host.
For discussion :
- When you send and read email through a web browser, say with gmail, which protocols do you think are being used between which computers? Draw some pictures.
spam
Mail has several issues:
- little to no authentication
- almost no cost ... and no incremental cost
... which has led to an explosion of spam.
- wikipedia: e-mail spam
- One estimate quoted there is that 90% of all 2008 email traffic was spam.
- anti-spam techniques: filtering rules, greylists, dns-based lists, ...
- Also see
- anonymizers
bittorrent
I know that Sean is interested in peer to peer
stuff, not just server/client.
One of the best know of those is BitTorrent,
so it's worth talking some about how that works.
We'll see how far we get.
Terminology:
- peers
- torrent file
- seeder
- leecher
- tracker
- distributed trackers / DHT / peer exchange
One of best known listing sites:
Discuss legality.
