Archive for January, 2008
Ubuntu! Its fun to say!
Posted by michaelhamel in Linux on January 28, 2008
We have a fairly standard home networking setup – a DSL modem, a wireless router, and a hub distributing 100BaseT to some RJ-45 sockets scattered about the house. The modem and the router both have firewalls and web interfaces to them, but neither of them are very versatile. For example, one thing they can’t do is log traffic on a per-IP basis, so when we start using 500Mbytes/day they can’t tell me which machine in the house it is coming from. We have a bandwidth cap, above which our ISP chops us back to 64Kbits up and down, so that can be important. Nor can the DSL modem firewall send mail to me logging firewall rejects, so sometimes when something doesn’t work it can be difficult to tell whether its the PC, the firewall, or something broken in the outside world. A proper firewall can do all these things and a lot more, as I know from running an OpenBSD-based firewall for my employer for the last ten years. And the firewalls in DSL modems don’t have such a great reputation for security. Holes have been found in some. Our modem has an additional peculiarity; it insists on running a DNS cache and providing its own address as a DNS server to local machines. Unfortunately the cache isn’t all that great and falls over every two or three days. The only solution is to turn the modem off and on, which is a bit vexing.
So that was one reason to look at installing a separate stand-alone machine to act as a firewall. Read the rest of this entry »
Ripple control noise suppressor
Posted by michaelhamel in Electronics on January 23, 2008
Ripple control is a technique used by electricity companies to control loads. Its rather primitive, but that’s because it dates back to Before Computers, and its still done today with ingenious electromechanical hardware. The idea is that the electricity company can reduce peak loads by broadcasting signals over the mains wiring, that switch off consumer’s appliances. This may sound like a Bad Idea – why would anyone agree to it? But there are some sorts of quite substantial loads which can be switched on or off by the electricity company without causing any grief, the prime example being household water heating. The thermal mass and insulation of your hot water cylinder mean that it doesn’t matter if the power is switched off to it for an hour or so. So all hot water cylinders are required to be on a seperate ripple-controlled circuit, which is what one of those mysterious boxes in your household fuse box is doing. And every day, the electricity company sends out signals to turn it on and off. They also send out different signals to turn on or off various industrial loads, street lighting, and so on. Read the rest of this entry »