Transparent proxy support in linux 2.4 ?

[Roberto Zunino]

How can I simulate the linux 2.2.x transparent proxy support in linux 2.4?

Using linux 2.2 on my router I can bind() a socket to an address X and
then connect() to another host Y. Y would see an incoming connection from
X and reply accordingly: if the replies towards X pass through my router
they are rerouted towards the local socket and all works smoothly.

This is a (IMO) tricky hack to fake requests from host X: it is used for
example by nat-enabled IDENT servers that forward the incoming requests
towards the right host on the internal network. Normally the IDENT server
on these hosts wouldn't answer queries from hosts != X and therefore the
router has to fake the connection from X.

Linux 2.4 doesn't have this behaviour. Setting ip_nonlocal_bind doesn't
help. Maybe it could be done with some SNAT and libiptc & friends,...

Maybe there is a simpler way. Does anyone know one?

TIA,
Zun.