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We said that TCP and UDP identify applications using 16-bit port numbers. How are these port numbers chosen?
Servers are normally know by their well known port numbers.
See also services.
dent "@(#)services 1.16 97/05/12 SMI" /* SVr4.0 1.8 */
#
# Network services, Internet style
#
tcpmux 1/tcp
echo 7/tcp
echo 7/udp
discard 9/tcp sink null
discard 9/udp sink null
systat 11/tcp users
daytime 13/tcp
daytime 13/udp
netstat 15/tcp
chargen 19/tcp ttytst source
chargen 19/udp ttytst source
ftp-data 20/tcp
ftp 21/tcp
telnet 23/tcp
smtp 25/tcp mail
time 37/tcp timserver
time 37/udp timserver
name 42/udp nameserver
% date
Fri Jan 23 14:39:50 EST 1998
% telnet
styx.informatik.uni-osnabrueck.de 13
Trying 131.173.12.166...
Connected to styx.informatik.uni-osnabrueck.de.
Escape character is '^]'.
Fri Jan 23 20:39:58 1998
Connection closed by foreign host.
% telnet styx.informatik.uni-osnabrueck.de 21
Trying 131.173.12.166...
Connected to styx.informatik.uni-osnabrueck.de.
Escape character is '^]'.
220 styx FTP server (Version 5.1 (NeXT 1.0) Tue Aug 27, 1996) ready.
help
214- The following commands are recognized (* =>'s unimplemented).
USER PORT STOR MSAM* RNTO NLST MKD CDUP
PASS PASV APPE MRSQ* ABOR SITE XMKD XCUP
...
REIN* MODE MSND* REST XCWD HELP PWD MDTM
QUIT RETR MSOM* RNFR LIST NOOP XPWD
214 Direct comments to ftp-bugs@styx.
user bischof
331 Password required for bischof.
pass not_here
230 User bischof logged in.
stat
211- styx FTP server status:
Connected to 129.3.20.4 (129.3.20.4)
Logged in as bischof
TYPE: ASCII, FORM: Nonprint; STRUcture: File; transfer MODE: Stream
211 End of status
pwd
257 "/tmp_mnt/home/bischof" is current directory.
type i
200 Type set to I.
% ftp -dv styx.informatik.uni-osnabrueck.de 21
Connected to styx.informatik.uni-osnabrueck.de.
220 styx FTP server (Version 5.1 (NeXT 1.0) Tue Aug 27, 1996) ready.
Name (styx.informatik.uni-osnabrueck.de:bischof):
---> USER bischof
331 Password required for bischof.
Password:
---> PASS not_here
230 User bischof logged in.
ftp> ls
---> PORT 129,3,20,4,153,92
200 PORT command successful.
---> NLST
150 Opening ASCII mode data connection for file list.
.Xdefaults
.bashrc
Fake an e-mail (This is not leagal)
% telnet ilon 25
Trying 129.3.20.4...
Connected to ilon.
Escape character is '^]'.
220 ilon.cs.oswego.edu Sendmail SMI-8.6/SMI-SVR4 ready at Fri, 6 Feb 1998 13:16:26 -0500
help
214-Commands:
214- HELO MAIL RCPT DATA RSET
214- NOOP QUIT HELP VRFY EXPN
214-For more info use "HELP <topic>".
214-smtp
214-To report bugs in the implementation contact Sun Microsystems
214-Technical Support.
214-For local information contact postmaster at this site.
214 End of HELP info
Helo ilon
250 ilon.cs.oswego.edu Hello ilon [129.3.20.4], pleased to meet you
MAIL FROM: THE_BLUES_BROTHERS
250 THE_BLUES_BROTHERS... Sender ok
RCPT TO: bischof
250 bischof... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
Hi,
250 NAA24290 Message accepted for delivery
quit
221 ilon.cs.oswego.edu closing connection
Connection closed by foreign host.
%
I got:
From THE_BLUES_BROTHERS@cs.oswego.edu Fri Feb 6 13:17:57 1998
Return-Path: <THE_BLUES_BROTHERS@cs.oswego.edu>
Received: from ilon.cs.oswego.edu by cs.oswego.edu (SMI-8.6/SMI-SVR4)
id NAA15319; Fri, 6 Feb 1998 13:17:56 -0500
Received: from ilon by ilon.cs.oswego.edu (SMI-8.6/SMI-SVR4)
id NAA24290; Fri, 6 Feb 1998 13:17:42 -0500
Date: Fri, 6 Feb 1998 13:17:42 -0500
From: THE_BLUES_BROTHERS@cs.oswego.edu
Message-Id: <199802061817.NAA24290@ilon.cs.oswego.edu>
Apparently-To: bischof@cs.oswego.edu
Content-Length: 5
Hi,
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Last modified: 08/May/98 (11:53)