Lwip send udp packets larger than MTU, but my pc can not reassemble them

Question

I use lwip-1.4.1 and stm32f407.
my lwip can send udp packets to pc, but my pc would fail to reassemble when the udp packets are larger than MTU.
I use wireshark to check these packet context, but the fragmented udp packets from my lwip look as good as normal fragmented udp packets.

The following link is the record from wireshark:
https://dl.dropboxusercontent.com/u/1321251/test.pcapng

Thanks

Answer 1

IP will reassemble fragmented packets, but UDP can only deliver entire datagrams, so it relies on all the fragments having arrived. If they don't, the datagram must be dropped. For that reason it customary to restrict UDP datagrams to the MTU, or less, and indeed most unwise to do anything else.