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https://github.com/mjuric/udpfwd

User-space packed forwarded
https://github.com/mjuric/udpfwd

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User-space packed forwarded

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README 

        
udpfwd -- Userspace UDP relay.

==============================



Think of it as poor man's single-port UDP DNAT/SNAT.



Usage:



	./udpfwd   



The relay listens for packets received on listen_port, changes their source

IPs to the IP of the local host ("SNAT"), and forwards them to the

destination (dest_ip:dest_port) from a randomly chosen local send_port. The

selection of send_port is made on reception of the first packet from a given

source_ip:source_port; once chosen, the source_ip:source_port:send_port

triplet is unique, allowing for connection tracking. Therefore, when a

packet is received on send_port, its destination is changed to

source_ip:source_port ("DNAT"), and forwarded onwards.



Effectively, this is a userspace SNAT/DNAT.



Schematic:



                         +----------------+

 [host_a:xxxx] <-------> |          a_out:| <-------> [                   ]

 [host_b:yyyy] <-------> |:listen   b_out:| <-------> [ dest_ip:dest_port ]

 [host_c:zzzz] <-------> |          c_out:| <-------> [                   ]

                         +----------------+



*****************************************************************

*Warning:*



This relay has no authentication or authorization mechanisms, nor

does it in any way obscure or encrypt the forwarded packets. You

have been warned.

*****************************************************************



Getting the Sources

===================



Download them from http://www.sns.ias.edu/~mjuric/udpfwd[]



Building and Installing

=======================



A simple



	cd src && make



should do. Then copy the executable `udpfwd' to wherever you like (e.g.,

/usr/local/bin).



Logging

=======



A connection log and status file will by default be created in subdirectory

'log' of the directory from which you start udpfwd. If the the log file

cannot be written for any reason, logging will be disabled.



You can change the log and status file destinations using the --log and

--status command line options.



Where is this useful

====================



Wherever you don't have control over kernel-level routing/forwarding. For

example, when attempting to set up an OpenVPN tunnel on an OpenVZ VPS where

the hosting company disallows access to IP forwarding (I'll let you figure

out the details :-)).



Testing

=======



Two other tools are included in the package, mainly to make the testing

easier. They are:



	./reflect 



		UDP packet reflector -- returns received packets to the

		sender



	./send    [seconds_between_packets=1]



		Sends a stream of UDP packets to dest_ip:dest_port. UDP

		packets are sent from source_port. When a packet is sent,

		waits for 1 second for a reply. After receiving the reply

		(or after 1 second expires), waits for

		seconds_between_packets seconds and repeats.



You may use these to test the relay. E.g.



	Host A:  ./relay   Host_B 5000 4999

	Host B:  ./reflect 5000

	Host C:  ./send    Host_A 4999 6000



In the example above, ./send (executed on Host_C) will send packets from port

6000 to Host_A's port 4999. ./relay will forward these to Host_C's port

5000. These will be reflected by ./reflect and passed back through the relay

to ./send.



License and Warranty

====================

Copyright (C) 2008 Mario Juric 



This program is free software; you can redistribute it and/or modify it

under the terms of the GNU General Public License, Version 2, as published

by the Free Software Foundation.



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.



You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307

USA