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The "libnetfilter_cthelper" project

What is libnetfilter_cthelper?

libnetfilter_cthelper is the userspace library that provides the programming interface to the user-space helper infrastructure available since Linux kernel 3.6. With this library, you register, configure, enable and disable user-space helpers. This library is used by conntrack-tools.


libnetfilter_cthelper requires libmnl and a kernel that includes the nfnetlink_cthelper subsystem (i.e. 3.6 or later).

Main Features

  • registering user-space helpers
  • retrieving existing helpers

For the nfnetlink_cthelper subsystem.


You can check the library documentation generated in doxygen format.

Git Tree

The current development version of libnetfilter_cthelper can be accessed at


libnfnetlink_cthelper has been written by Pablo Neira Ayuso.

Copyright © 1999-2014 Harald Welte, Pablo Neira Ayuso . Pablo Neira Ayuso