[svlug] port forwarding

Dave Zarzycki dave at loki.sbay.org
Sun Nov 29 16:21:15 PST 1998


On Sun, 29 Nov 1998 garry at jackson.ml.org wrote:

> does nayone know how to set up a program to forward a port on the internet
> to a port on a internal behind the firewall machine.

There are two ways of doing this.

One is at the application level with programs such as redir or
simpleproxy.

The other way, and the way that I like best, is to use the kernel.

linux 2.2 will support something called ipportfw, which does what you want
at the kernel level. This not only offers the advantage of being faster,
but has the added feature of re-writting the packet "to" address to the
real machine, while leaving the "from" address alone. (application level
proxies can't do this.)

If you want an application level proxy, go look over at sunsite.unc.edu
via ftp.

I would recommend the kernel level approach to most people:

http://www.monmouth.demon.co.uk/ipsubs/portforwarding.html

If you are not running recent 2.1 kernels, you can get a patch for 2.0.

davez


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