RN314 iptables NAT support, openvpn

Hello,

I use the RN314 with the OS 6.6.0.

Seems some modules are missing by default in the kernel.
I am trying to configure openvpn. It works to acces to my NAS remotely, but to redirect all internet browsing through the vpn I need to add some nat rules like :

$ sudo iptables -t nat -I POSTROUTING -o eth1 -s 10.8.1.0/24 -j MASQUERADE
iptables v1.4.21: can't initialize iptables table `nat': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.

It seems possible to build the kernel with this module, but why Netgear does not add this module natively ? or what is the easyest workaround ?

Thanks for your help !