Use external IPs from Internal Network (NAT)

["Christoph Gassmann" <christoph.gassmann@aquantum.net>]

Hello List,

I´m trying to do a firewall with NAT. For now my firewall makes DNAT. It
maps the external IPs to an internal IP. Like this:

$IPT -t nat -A PREROUTING -d $SPHERE_EXT_IP -j DNAT --to $SPHERE_INT_IP

and I allow some ports in the forward chain. Everything works fine.

I want to use the external IPs from the internal Network too.
I know I have to do it with the OUTPUT -t nat chain, but my rules are
not functioning.

$IPT -t nat -A OUTPUT -d $SPHERE_EXT_IP -j DNAT --to $SPHERE_INT_IP

but nothing happens.

What am I doing wrong?

Thx for your help.
Christoph