Networking :: Access Firewall Public IP From Internal NATed DMZ Machine?

I could no handle/circumvent on the past week, despite of the several "googling" and documents reading. I will try to mention all needed bits... I'm managing a network with the following structure:

eth0: internal net
eth1: DMZ
eth2: 10 mbit/sec sync line with eight public /29 IP's + a /30 interconnection network. All public IP's must use the interconnection's network gateway.
eth3: ADSL with ppoe with fixed IP (ppp0).

Now, a few extra info:

- All internal traffic is routed through ppp0 except when it's destined for DMZ and public IP's range.
- DMZ traffic is routed either through ppp0 or eth2. This is done by source IP.
- eth2 has on IP from the interconnection network, and six public IP's are also defined on eth2. Command: "ip addr add ...."

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