Cedric, Indeed it looks like the SYN+ACK is not understood.
The packets look OK to me.
Have you also tried it with the normal IPv4 library?
Your PCAP file shows checksum errors. In most cases this is a false alarm, it is caused by the so-called checksum offloading.
Just to be sure, can you deactivate all CRC offloading? It’s a property of the driver and they are normally called:
- IPv4 Checksum Offload
- UDP checksum Offload (IPv4)
- UDP checksum Offload (IPv6)
- TCP checksum Offload (IPv4)
- TCP checksum Offload (IPv6)
As a network developer I have them switched off all the time.
Also I will forward you the latest version of +TCP /multi by email.