I progress on my tunnel by Udp over Internet.
I find that the load of udp packet is (hard-coded) troncated to 220.
I tried to adjust size of data to buffer size, so I replace "220" by "ENC28J60::buffersize-42"
ALAIK, it seems possible.
Any remark welcome.
I have also to grow length type from uint8_t to uint16_t !