port forwarding problem. Probably easy if you know how.

[hendrik@topoi.pooq.com]

I'm running sarge on a vintage Pentium as a gateway machine for a home 
network.

My machine was cracked last December and I reinstalled everything
from scratch using a sarge netinstall CD. (I checked all scripts I 
resurrect from the old system,  and recompiled all my *own* binaries 
from original source code.  The script I mention below hasn't been 
molested.)

I run the same script for port-forwarding and masquerading that I used 
before the reinstall.

But it doesn't work.

Lines like

iptables -t nat -A PREROUTING --protocol tcp -d 216.138.195.194 --dport 27012 -j DNAT --to-destination 172.25.1.5:27012 --verbose
iptables -t nat -A PREROUTING --protocol udp -d 216.138.195.194 --dport 27012 -j DNAT --to-destination 172.25.1.5:27012 --verbose
iptables -t nat -A POSTROUTING --protocol udp -s 172.25.1.5 --sport 27012 -j SNAT --to-source 216.138.195.194:27012 --verbose
iptables -t nat -A POSTROUTING --protocol tcp -s 172.25.1.5 --sport 27012 -j SNAT --to-source 216.138.195.194:27012 --verbose

have no effect at all (as checked by iptables --list)

but the line

iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

works like a charm.

I suspect there's probably a missing kernel module.  But which one?
And where do I find it?  The docs for iptables way that it will attampt 
to load any necessary modules, so I presume a simple modprobe isn't 
enough.  Or else that it doesn't try hard enough.

-- hendrik