Can you create a FreeBSD gateway, with private IPs, without NAT/divert ?

[None Secure]

I've built a lot of gateways/routers with FreeBSD - but they have always been with real, routable IPs.

External IP is real, internal IP is real, and all I need is gateway_enable="yes" and a next-hop route from my ISP.

No NAT, no divert, no ipfw rules, nothing.

BUT, what if my ISP is giving me a private IP, and my internal network is also private IPs ?  External gateway address is 192.168.1.2 and internal gateway address is 10.10.10.1 ... the ONLY way I could make this work is with natd and ipfw divert rules.

My question is:  is it possible to have a network of non-routable IPs, and a gateway with non-routable Ips on internal and external interfaces, and NOT use natd/divert ?  Can it be done with no ipfw rules at all, just like I used to ?

Thanks.