Damn, damn, damn! Today I went to work and left my modem switched on and the home PC connected up — it was synchronising the latest bunch of photo files. I got home to find that the synchronisation hadn’t completed because it had been disconnected. Unfortunately my home PC is configured to dial-on-demand (something I’ve never got to the bottom of and disabled). The PC dialled up the modem bank, the modem bank answered, then failed to authenticate the connection, so it hung up. The PC waited two minutes and dialled up … repeated 91 times before we got home and turned the modem off!

Turns out that one of several systems that was decommissioned at work today was a box that runs a copy of radiusd. One of the three modem pools authenticates to that box, or tries to … the box had been switched off but the modem bank left on, hence the $30 phone bill.