I have a pcap file that I modified with tcprewrite to set source and destination IP = 127.0.0.1, while the port numbers are different. I also set both mac addresses to 00:00:00:00:00:00 as I understand that comms over localhost ignore MAC. I made sure checksum was fixed.
When I run tcpreplay -i lo test-lo.pcap
in one shell, and tcpdump -i lo -p udp port 50001
in another, I see the traffic. Yet, when I try to view the traffic with netcat -l -u 50001
, it sees nothing. Wireshark is capturing the traffic correctly.
Side note: I'm seeing the following warning when running tcpreplay on localhost:
Warning: Unsupported physical layer type 0x0304 on lo. Maybe it works, maybe it won't. See tickets #123/318
That seems worrisome.
I'm asking because my own UDP listener code is also having the same problem as netcat and thought that maybe I'm missing something. Why would traffic be seen by tcpdump and wireshark, and not by netcat?