Potential RFC non-conformance: RFC 9293 § 3.10.7.4

[tiferrei]

Hi there,

We have identified a potential implementation bug to do with handling unexpected packets in synchronized states. Namely, what the implementation should do when receiving a SYN packet in a connection established state.

Currently, it seems like the packet is simply dropped silently by smoltcp, when I believe that an ACK or RST would be required, as per Section 3.10.7.4.

We have a packet trace of this behavior below:

bug.pcap.zip

The particular exchange is packets 22 to 25 (inclusive). Packet 26 is sent by us at the end just to clear the test session.

I am happy to provide more details as needed, please just let me know.