The Netcat6 Homepage - HISTORICAL

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What is netcat6?


Since longer time, following implementations got native IPv6 support:

What is netcat6?

Netcat6 is a clone of the original netcat utility. From the netcat README:

      Netcat is a simple Unix utility which reads and writes data across network
      connections.  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

Netcat6 is a total rewrite of netcat, with several advantages:

  • It fully supports IPv6.

  • It is far more efficient, utilizing flexible buffering and minimal (or no) data copying or analysis.

  • The source is well structured, documented and very easy to follow. One of the main objectives of netcat6 is to produce an excellent example of AF independant networking and efficient data transfer. The code has minimal dependancy on the address family or protocol type and can be trivially extended to talk many layer 3 protocols.

  • Greatly improved configuration and platform indipendence.

  • Can support servers or clients that use TCP half-close.

Some features of the original netcat are not present in netcat6, either because they haven't yet been implemented or because there exists better tools for the job. See the TODO file included in the netcat6 package for more information.


In the simplest usage, "nc6 host port" creates a TCP connection to the given port on the given target host (using either IPv4 or IPv6 as appropriate). 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 applications which shut everything down and exit after an end-of-file on standard input.

Netcat6 can also function as a server, by listening for inbound connections on arbitrary ports and then doing the same reading and writing when a client connects. 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.

Netcat6 can also be used over UDP (using the '-u' or '--udp' option). UDP is an unreliable transport protocol, meaning some data can get lost, but it's a very useful capability to have.

Some of netcat6's major features are:

  • Outbound or inbound connections, using TCP or UDP over any suitable transport protocol available on the system (usually IPv4 or IPv6).

  • Full DNS forward/reverse checking, with appropriate warnings.

  • Ability to use any local source port.

  • Ability to use any locally-configured network source address.

  • Flexible data buffering and control of MTU.

  • Flexible control of connection shutdown.

Efforts have been made to have netcat6 "do the right thing" in all its various modes. One of the development principles is "the principle of least surprise". This means that netcat6 should do what you expect it to do. If you think it doesn't do something quite right, let us know and we'll look into it.

For more information, see the man page included in the netcat6 package.

Netcat6 is licensed under the GNU Public License (see the section called “Copyright”).


See the INSTALL file included in the netcat6 package for specific installation instructions. For those who can't wait, the following should do it:

# ./configure
# make
# make install


If the build fails on your system, please let us know so that we can fix the issue.


The authors of netcat6 are:


Netcat6 is licensed under the GNU General Public License, which you can find in the COPYING file included in the netcat6 package, or at the URL:

Updated 23.06.2014Sources | DeepSpace6

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