when trying to process udp packets in a simple socket based udp echo server with mtu size of 1500 bytes echo failed at packet payload size of 1472 bytes. Fixed this by changing hardware checksum to software checksum in low level ethernet unit function and enabling software checksum in lwipopts. Lwipopts provides no way of disabling hardware checksum. However after fine tuning lwipopts hit a barrier where can only echo back up to 32767 bytes. What options to set to increase this size up to 64kbytes?