Created attachment 127256 [details] tcpdump SUMMARY Running kdeconnect 1.13.6 on a Samsung tablet SM-835 Android 9. Trying to connect to my laptop. UDP packets are getting through but the laptop complains about unterminated string. Tcpdump shows a single UDP packet to port 1716 with truncated data. Laptop is Ubuntu 18.04. Connecting my Pixel phone (Android 10, also kdeconnect 1.13.6) to the laptop works fine. STEPS TO REPRODUCE 1. Run kdeconnector on Samsung tablet 2. tcpdump on laptop 3. OBSERVED RESULT Incomplete data in packet. EXPECTED RESULT Multiple packets or complete data.
Created attachment 127258 [details] tcpdump of phone startup
The tcpdump of the phone starting is slightly different. Both have truncated data but the UDP length from the phone is larger than the packet size. The phone sends a second UDP packet containing the rest of the data, this seems to trigger the laptop into starting a TCP session.
I think I somewhat understand what is going on. The UDP packet is too large to fit within the maximum transfer unit (MTU), usually 1500 bytes, or 1472 usable bytes. Therefore the "bad length 1631 > 1472" warning. While it seems possible to get around that via packet fragmentation this is apparently handled differently by devices. This could explain quite some "devices can't see each other" reports. I'm not quite sure how to address this. An obvious approach is to reduce the size of the identity packets, but that would be an incompatible change and would require careful rollout
*** This bug has been marked as a duplicate of bug 446238 ***