Hello, I am using the latest firmware RUTX_R_00.02.05.1 and modem firmware EG06ELAR04A04M4G and in NAT mode to EE with IPv4 and IPv6, I get both addresses fine (/64 for IPv6).
My main ISP provider has an L2TP service that when enabled provides me with the same IPv4 and IPv6 address ranges as my main DSL. The idea being that if the DSL fails, my main router switches traffic over the RUTX09 to 4G, the L2TP service tunnels the IP addresses as before (both IPv4 and IPv6). When setup from a Windows system or a BiPAC router it works fine for both IPv4 and IPv6 but with the RUTX09 it only provides IPv6, this is clearly a bug.