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Unix System Administration Handbook 1997 October
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netcat.txt
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INDEX ENTRY FOR NETCAT:
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Name: netcat - Reads or writes data across a network
Version: 1.10
Author(s): Hobbit <hobbit@avian.org>
On the CD-ROM in: network/netcat.tar
Ftp source: ftp.avian.org:/src/hacks/nc110.tgz
Web page: http://www.avian.org/web1/hak/netcat.html
Size on the CD: 215 KB (uncompressed)
Description:
Netcat is a simple Unix utility which reads and writes data across
network connections, using TCP or UDP protocol. It is designed to be
a reliable "back-end" tool that can be used directly or easily driven
by other programs 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 connections and some systems may have trouble
sending large amounts of data that way, but it's still a useful
capability to have.
Some of netcat's major features are:
+ Outbound or inbound connections, TCP or UDP, to or from any ports
+ Full DNS forward/reverse checking, with appropriate warnings
+ Ability to use any local source port
+ Ability to use any locally-configured network source address
+ Built-in port-scanning capabilities, with randomizer
+ Built-in loose source-routing capability
+ Can read command line arguments from standard input
+ Slow-send mode, one line every N seconds
+ Hex dump of transmitted and received data
+ Optional ability to let another program service established connections
+ Optional telnet-options responder
-- Adapted from the 1.10 README file
Advertised architectures:
Various releases of Ultrix, BSD, SunOS, Solaris, AIX, LINUX, IRIX,
OSF/1, FreeBSD, BSDI, NetBSD, HP-UX, UnixWare, A/UX, NEXTSTEP.
Prerequisites:
C compiler