This is just a light-weight implementation. Because we are making a Wi-Fi start kit, there are two network interface:
* one is a Soft-AP, which can let user access the network. Therefore, we use DHCP server to allocate IP address;
* one is a Wi-Fi station, which can associate an exist WLAN and access internet.
Then the NAT is used for address translation, from the network packet of Soft-AP to the WLAN network. I think it no need a sound, heavy realization. This component is just available in RT-Thread RTOS. I will make the NAT more effective and make the code style more like lwIP's, then submit it to lwIP. Thanks.
BTW, we also port lwip-head to the RT-Thread RTOS for dual IPv4/v6 stack. Welcome for testing too.