Just do "man nc" to see what you can do with this tool.
NAME
nc - TCP/IP swiss army knife
SYNOPSIS
nc [-options] hostname port[s] [ports] ...
nc -l -p port [-options] [hostname] [port]
DESCRIPTION
netcat is a simple unix utility which reads and writes data across network
connections, using TCP or UDP proto�
col. It is designed to be a reliable "back-end" tool that can be used directly
or easily driven by other pro�
grams and scripts. At the same time, it is a feature-rich network debugging
and exploration tool, since it can
create almost any kind of connection you would need and has several interesting
built-in capabilities. Netcat,
or "nc" as the actual program is named, should have been supplied long ago as
another one of those cryptic but
standard Unix tools.
In the simplest usage, "nc host port" creates a TCP connection to the given
port on the given target host.
Your standard input is then sent to the host, and anything that comes back
across the connection is sent to
your standard output. This continues indefinitely, until the network side of
the connection shuts down. Note
that this behavior is different from most other applications which shut
everything down and exit after an end-
of-file on the standard input.
Netcat can also function as a server, by listening for inbound connections on
arbitrary ports and then doing
the same reading and writing. With minor limitations, netcat doesn't
really care if it runs in "client" or
"server" mode -- it still shovels data back and forth until there isn't any
more left. In either mode, shutdown
can be forced after a configurable time of inactivity on the network side.
And it can do this via UDP too, so netcat is possibly the "udp telnet-like"
application you always wanted for
testing your UDP-mode servers. UDP, as the "U" implies, gives less reliable
data transmission than TCP connec�
tions and some systems may have trouble sending large amounts of data that
way, but it's still a useful capa�
bility to have.
You may be asking "why not just use telnet to connect to arbitrary ports?"
Valid question, and here are some
reasons. Telnet has the "standard input EOF" problem, so one must
introduce calculated delays in driving
scripts to allow network output to finish. This is the main reason netcat
stays running until the *network*
side closes. Telnet also will not transfer arbitrary binary data, because
certain characters are interpreted
as telnet options and are thus removed from the data stream. Telnet also emits
some of its diagnostic messages
to standard output, where netcat keeps such things religiously separated from
its *output* and will never mod�
ify any of the real data in transit unless you *really* want it to. And of
course telnet is incapable of lis�
tening for inbound connections, or using UDP instead. Netcat doesn't have
any of these limitations, is much
smaller and faster than telnet, and has many other advantages.
OPTIONS
-g gateway source-routing hop point[s], up to 8
-G num source-routing pointer: 4, 8, 12, ...
-h Display help.
-i secs delay interval for lines sent, ports scanned
-l listen mode, for inbound connects
-n numeric-only IP addresses, no DNS
-o file hex dump of traffic
-p port local port number (port numbers can be individual or ranges: lo-hi
[inclusive])
-q seconds Quit after EOF is detected on stdin and after a delay. "-q 0"
makes "nc" quit as soon as EOF is
detected.
-r randomize local and remote ports
-s addr local source address
-t Enable telnet negotiation
-u UDP mode
-v verbose [use twice to be more verbose]
-w secs timeout for connects and final net reads
-z zero-I/O mode [used for scanning]
COPYRIGHT
Netcat is entirely my own creation, although plenty of other code was used
as examples. It is freely given
away to the Internet community in the hope that it will be useful, with no
restrictions except giving credit
where it is due. No GPLs, Berkeley copyrights or any of that nonsense. The
author assumes NO responsibility
for how anyone uses it. If netcat makes you rich somehow and you're feeling
generous, mail me a check. If you
are affiliated in any way with Microsoft Network, get a life. Always ski in
control. Comments, questions, and
patches to [EMAIL PROTECTED]
BUGS
Efforts have been made to have netcat "do the right thing" in all its various
modes. If you believe that it is
doing the wrong thing under whatever circumstances, please notify me and
tell me how you think it should
behave. If netcat is not able to do some task you think up, minor tweaks to
the code will probably fix that.
It provides a basic and easily-modified template for writing other
network applications, and I certainly
encourage people to make custom mods and send in any improvements they make to
it. Continued feedback from the
Internet community is always welcome!
Some port names in /etc/services contain hyphens -- netcat currently will not
correctly parse those, so specify
ranges using numbers if you can.
SEE ALSO
/usr/share/doc/netcat/README.gz
AUTHOR
This manual page was written by Joey Hess <[EMAIL PROTECTED]> and Robert
Woodcock <[EMAIL PROTECTED]>, cribbing
heavily from Netcat's README file.
Netcat was written by a guy we know as the Hobbit <[EMAIL PROTECTED]>.
NC(1)
Matthieu NOURY
Ing�nieur Syst�mes et R�seaux
(Unix, Linux)
Ozitem - ex CLS R�seaux et Syst�mes
T�l. : 01 41 99 11 11; Fax : 01 41 99 11 12
mailto:[EMAIL PROTECTED]
http://www.ozitem.com
-----Message d'origine-----
De�: Mike Dawg [mailto:[EMAIL PROTECTED]]
Envoy�: mercredi 29 mai 2002 20:51
��: Sec; [EMAIL PROTECTED]
Objet�: RE: Using Netcat
First of all, download it from:
http://www.atstake.com/research/tools/index.html#network_utilities
and for learning how to use it, I'm sure you can search the web,
www.google.com. There is also a book called "Hacking Linux Exposed" the
covers just a few of the uses of it.
That should be enough to get you started.
Mike
> -----Original Message-----
> From: Sec [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, May 28, 2002 11:47 AM
> To: [EMAIL PROTECTED]
> Subject: Using Netcat
>
>
> I have not installed netcat before on Linux. It is apparently included
> in my Linux. How can I start using / install it ?
>
