netredirect allows you to redirect all outbound connections made
from a given program to another host. For example:
netredirect 127.0.0.1 8080 curl http://www.google.com
will send the request to port 8080 on localhost!
Because of the method that netredirect uses to achieve its result only
programs that use network system calls through libc wrappers can be
redirected.
When the host or port argument to netredirect is original then the
original value is preserved. That allows you to perform host-only and
port-only redirection.
In order to install do the following:
git clone https://github.com/grn/netredirect
cd netredirect
make all
Then as root:
make install
The files are installed under /usr/bin and /usr/lib by default. The
locations can be changed by passing BIN_PATH and LIB_PATH variables
to make. If you want to install under /bin and /lib do the following:
make BIN_PATH=/bin LIB_PATH=/lib install
Now you are ready to use it!
Uninstallation is left as an exercise to the user.
The original motivation for this program was load/stress testing of a
service that used lots of external services. In order to test its
production configuration without generating significant load on these
services a redirection method was necessary. netredirect allows to
perform such tests with ease!
The tool is extremely simple. The best way to understand it is to look
at the source code. Basically it uses LD_PRELOAD trickery to wrap the
connect function of libc with its own. The target IP address is
stored in an environment variable that our library accesses. The
environment is prepared by the netredirect script.
- currently
netredirectandlibnetredirect.somust be in the same directory - currently only TCP is supported
- may break DNS name resolution if done over TCP
NETREDIRECT_HOSTmust be an IPv4 address in the dotted notation- no UDP or IPv6 support
- no error checking in the
netredirectscript