Install packages
opkg update
opkg install kmod-ipt-nat6
Run ip6tables -t nat -L
Error:  ip6tables v1.4.21: can’t initialize ip6tables table `nat’: Table does not exist (do you need to insmod?)
Perhaps ip6tables or your kernel needs to be upgraded.

Solutioin:
The original ipv6 nat6 requires a kernel version of 3.9.0 or higher and an iptables version of 1.4.8 or higher.
Upgrade the corresponding kernel and iptables packages to solve the problem.