After an extended downtime on my ADSL uplink at home during a nice snowstorm, I got curious and wanted to find out the SNR (Signal to Noise Ratio) I had on my line, to try to explain why it was down.
It turned out it was more complicated than I thought, because the modem was locked down by Bell Canada (even though I am not a customer). There was a Windows utility, but since I haven't been running this pathetic operating system in years, I had to find an alternative.
Fortunately, the author of that utility posted a description of the packet format used for the password reset, and here I was trying to send raw ethernet frames using Linux (for testing and, why not!) and FreeBSD (because I use FreeBSD for routing, because I dislike iptables).
The result is this somewhat poorly written C program, available in this git repository. It uses raw sockets in Linux but the BPF (Berkeley Packet Filter) in FreeBSD, as their interface is a little broken for raw sockets.
See the README file for more information.