We have FPGAs carrying on conversations with other FPGAs all the time. Frequently we use layer 2 Ethernet between known devices on a LAN, although we are working our way up to layer 3. Wireshark is a go-to tool to see what is going on and share pcap captures with our colleagues. But how do you see the traffic between two FPGAs on a LAN when they are talking to each other? Port Mirroring!
We had been playing all kinds of games before we found this little gem: the Netgear GS105E. $60 to Amazon, a dorky Windows configuration dance, and we feel we've found just the ticket for our packet capture needs. We set ours up to only mirror the ingress from ports 1 and 2 to port 5. We plug our chatty FPGA board into ports 1 and 2 and anything running Wireshark into port 5. Ta dah. No more sending broadcast packets just to see what is going on!