NAME

tgcd - TCP/IP Gender Changer Daemon utility

SYNOPSIS

tgcd -C -s<host:port> -c<host:port> [-i<n>] [-k<n>] [<common options>]
tgcd -L -p<port> -q<port> [-k<n>] [<common options>]
tgcd -F -p<port> -s<host:port> [<common options>]

DESCRIPTION

tgcd is a simple Unix network utility to extend the accessibility of TCP/IP based network services beyond firewalls. This can also be used by network analysts and security experts for penetration testing and analyze the security of their network. It has three different modes:

- ConnectConnect (or CC, specified by option -C)
- ListenListen (or LL, specified by option -L)
- Port Forwarder (or PF, specified by option -F)

The ConnectConnect and ListenListen instances of tgcd are used jointly together, while the Port Forwarder mode acts standalone.

The ConnectConnect instance resides somewhere on the network (inside the LAN) where it can access the desired server, while the ListenListen will be where the external client can access it (outside the LAN). The ConnectConnect instance, when started, tries to establish a control connection to ListenListen instance (if failed it will retry every n seconds specified by -i ).

The ListenListen instance upon receiving a connection from client, will send a request to ConnectConnect (over the already established control connection) to establish a connection to server as well as another connection to ListenListen for data transferring.

In the Port Forwarder mode, tgcd will pump data from one port to another providing a basic port forwarding functionality.

For all three modes, one can choose (using -m option) between two different ways of handling multiple connections. By choosing the Select method, the program will use less system memory in expense of slower handling of multiple connections, and on the other side by choosing Fork method tgcd will handle the multiple connections faster in expense of system memory.

tgcd links with libwrap (if available at build time) to provide a simple access control mechanism that's provided by hosts_access(5).

Aside from libwrap support, since version 1.0.2 an executable can also be passed to tgcd (using -f or --filter argument) to perform whether or not accept a connection. The script takes the incoming IP address as the parameter, and its exit code indicates whether or now tgcd should accept the connection or not. Exit code 0 means to accept, non-zero means to reject the incoming connection. The filter feature only takes effect on LL and LC nodes.

OPTIONS

-C, --ccnode

Become a CC (ConnectConnect) node.

-s, --server <host:port>

The host and port of the actual server

-c, --llhost <host:port>

The host and port of the ListenListen node.

-i, --interval <seconds>

Time interval to periodically report to LL (default: 40s).

-k, --key <number>

poorman's encryption (0-255, default: 0, means no encryption)

Options for ListenListen mode:

-L, --llnode

Become a LL (ListenListen) node.

-q, --llport number

The port to listen on for incoming connection from a CC node

-p, --port number

The port to listen of for incoming actual client connection

-k, --key number

poorman's encryption (0-255, default: 0, means no encryption)

Port forwarder options:

-F, --lcnode

Become a ListenConnect node, i.e. just a simple port forwarder

-p, --port number

The port to listen of for incoming actual client connection

-s, --server host:port

The host and port of the destination server

Common options:

-m, --method {f|s}

f: Fork s: Select (default: s)

-f, --filter filter

Optional argument to run filter on new connections, IP passed as argument

-l, --log file

Write logs to file. (default:'/dev/null')

-g, --level number

Log level detail (default:0).

-n, --nodaemon

Do not become daemon

-h, --help

Display this.

-v, --version

Display version number.

EXAMPLES

Lets say you'd like to access a localy running WEB server on your work PC from home, this is how to do it:

To run tgcd in CC mode and provide access to the local WEB server :

tgcd -C -s localhost:80 -c my_home_computer:1234

To run tgcd in LL mode on my_home_computer host to provide access to the above service:

tgcd -L -p 8000 -q 1234

This will make the WEB server running on the work PC accessible on port 8000 of my_home_computer.

SEE ALSO

hosts_access(5)

AVAILABILITY

tgcd is tested on Linux 2.2.x (x86), 2.4.x (x86), 2.6.x (x86, ARM9, AVR32), Cygwin (1.5.x), and NetBSD 2.1.0
Please feel free to send us your patches to get tgc working on other platforms.

COPYRIGHT AND LEGAL ISSUES

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

Disclaimer:

This program is provided with no warranty of any kind, either expressed or implied. It is the responsibility of the user (you) to fully research and comprehend the usage of this program. As with any tool, it can be misused, either intentionally or unintentionally. THE AUTHOR(S) IS(ARE) NOT RESPONSIBLE FOR ANYTHING YOU DO WITH THIS PROGRAM or anything that happens because of your use (or misuse) of this program.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

AUTHOR

tgcd is written by Faraz.V (faraz@fzv.ca)