port redirection

[g3gg0]

hiho 🙂

i want to code a library/routine/service/anything which intercepts the TCP
data sent to port 25 and redirects that data to lets say port 10025.
some other service at port 10025 then does *some work* on the data and sends it
internally to the *real* port 25.

is there a chance to configure windows’ firewall to redirect data sent from
an external interface to port 25 to our port 10025?

does anyone have an idea how to solve this EXCEPT using custom LSP/TDI/NDIS drivers?

thank you very much in advance 🙂

[Vadim Smirnov]

is there a chance to configure windows’ firewall to redirect data sent from an external interface to port 25 to our port 10025?

Windows built-in firewall does not support port redirecting services.

does anyone have an idea how to solve this EXCEPT using custom LSP/TDI/NDIS drivers?

Regretfully there is no other way. You can use WinpkFilter library (http://www.ntkernel.com/w&p.php?id=7) to implement port redirector solution though.

[g3gg0]

thanks so far 🙂

is it possible to get that port redirect dynamically upon startup of “my_app”?

i want the user to start my program and just *then* it should care
for some ports and filter them.
if the user is shutting down my_app, it should disable port redirections
and the user’s system should be in the state is was before.

b.r.

[Vadim Smirnov]

is it possible to get that port redirect dynamically upon startup of “my_app”?

WinpkFilter driver should be installed on the system before hand. But in any case you start filtering/redirecting packets only when your application is active and stop this when your application is terminated. So the answer is YES.

[g3gg0]

since that app should be part of a kind of installer which gathers information
about the local services and its usage, it is required that this port redirection
is done without a prior reboot (to install your service) 🙁

the system on which we “work” *must not* be rebooted at any time since
its a productional system.

is that doable?

[Vadim Smirnov]

That can be a problem, dynamic hooking into system stack (with dynamically loadable NDIS IM driver under Windows 2000+ and dynamic hooking driver for earlier Windows versions) can be implemented bu it less reliable and more complex than static (in case of IM driver reboot still can be required in some cases).

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