This is part 2 of the homelab PTP grandmaster series. Part 1 used a Raspberry Pi CM4 with SatPulse. This build uses a NanoPi R5S-LTS and takes a different path to the same destination. The R5S has no standard GPIO header. It has an FPC connector. Getting a GPS module talking to it required a breakout board, a ribbon cable, a soldering iron, and more debugging than expected. The results made it worth it. ...
I work with industrial infrastructure that requires nanosecond-accurate time synchronization. The commercial GPS-disciplined PTP grandmaster clocks that solve this problem run from several thousand dollars on the low end, and considerably more with options and support. I had CM4s and CM4 IO boards already sitting in the lab. A TimeHAT with an OCP M.2 GNSS module would have been the cleaner path at around $400, but that is steep when the goal is learning how PTP actually works, not deploying production infrastructure. This build came in at around $103 in new parts. ...
Two NICs, one subnet. Seems fine. It isn’t. I frequently run into this on Linux servers, PTP Grandmaster clocks, telemetry acquisition and analysis servers, industrial controllers and other appliances where Linux is running under the hood whether the vendor advertises it or not. Most of them cover this limitation somewhere in their published documentation. It is worth reading before you plug in the second cable. The symptoms are always the same: traffic arrives on one interface, replies leave on another, sessions drop for no apparent reason, and nothing in the logs explains it. ...
I inherited a set of Ubuntu servers that were provisioned outside of our normal provisioning and configuration methods of Foreman and Ansible, talking to Windows DHCP servers that use DHCP Option 81 for dynamic DNS registration. The problem was that some servers were getting their DNS A records registered correctly and some were not. The inconsistency was problematic, and the more I dug into it, the worse it got. This is the story of chasing that inconsistency, finding a workaround, realising the workaround was unnecessary, and ending up with a PR open against systemd upstream to fix a man page that has been inconsistent and ambiguous for years. ...