I have customer in a very remote location with a DSL router/modem with a /30 subnet assigned to it's WAN interface. The upper of the two available IP addresses is used for the router and the lower for the ISP's gateway on the other side of the DSL link. The LAN network is on a private range using NAT.
I want to change the router/modem to use only public IP addresses and have another Ethernet router behind that router which has more features (i.e. IPSec etc.) and put the private network on the LAN port of the router.
I've come to do so and I now think it is impossible because a /30 does not give me enough IP addresses. Is this correct?