On 05/13/2010 02:52 PM, Steven Bellovin wrote: > On May 13, 2010, at 2:24 04PM, Daniel Senie wrote: > > >> While the equipment may well be affected by an EM pulse, if the gear returns >> to normal after a power cycle, then the equipment vendor didn't do their job >> fully developing the product. A product should be tested to take such pulses >> and should recover provided it has not suffered a catastrophic failure (and >> in fact it should contain sufficient protection to avoid such in most cases). >> >> In working on one particular router in the lab some years ago, I was >> verifying some software functionality and the hardware engineer I was >> working with reached over my shoulder and used a device that delivered a >> high voltage spike (simulated lightning) to a 10BaseT network port. After I >> peeled myself off the ceiling (and he stopped laughing), we set to work >> figuring out how to get the device to self-reset after such a strike. One >> component, an Ethernet hub chip, got into a confused state. I was able to >> detect this in software, so we adjusted the product design so that the >> software could yank the hub chip's reset line. >> Luck. I've needed that kind of reset a few times... >> It's unfortunate that products, both hardware and software, receive minimal >> quality testing these days. Guess it's not a surprise, since buyers seemed >> to prefer products that were quick to market, with lots of bugs, rather than >> reliability and resilience. >> That is certainly true (and not entirely modern; you can read about that problem in old roman literature. When was "Zen and the art of motorcycle maintainance" written? - 1970's); however it is nearly impossible to protect well against close-by lightning. >> > It's not just a matter of "these days" -- lightning is awfully hard to deal > with, because of how quirky the real-world behavior can be. I had to deal > with this a lot in the 1970s on RS-232 lines -- we could never predict what > would get fried. Of course, there was also a ground strikes very near my > apartment, where the induced current tripped a circuit breaker, blew out a > couple of lightbulbs, and and came in through the cable TV line to fry the > cable box, fry the impedance-matching transformer, and fry the RF input stage > on the television... > I can second Steve in spades; I used to work for the power company in Alabama... There you learn a LOT more than you ever wanted to know about lightning. Consider that one hit can destroy the inside of a >10Mw 66kv->12kv distribution transformer (I actually saw the strike involved; it was less than a mile from my apartment at the time, and dropped power to me; the apt was fed from an entirely different company... My power came back in a few minutes; the other load took almost a week (they had a redundant feed; it was a hospital, but they ran in a low-power mode till a BIG crane and big lo-boy truck came with another transformer)); how are you going to protect any computer from *that*...
-- Pete > --Steve Bellovin, http://www.cs.columbia.edu/~smb > > > > > > > >
