[126377] in North American Network Operators' Group
Re: POE switches and lightning
daemon@ATHENA.MIT.EDU (Steven Bellovin)
Thu May 13 14:52:45 2010
From: Steven Bellovin <smb@cs.columbia.edu>
In-Reply-To: <EF234211-FDC4-44A4-B87C-607705DE7D27@senie.com>
Date: Thu, 13 May 2010 14:52:19 -0400
To: Daniel Senie <dts@senie.com>
Cc: nanog@nanog.org, Pete Carah <pete@altadena.net>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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).
>=20
> 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.
>=20
> 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.
>=20
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...
--Steve Bellovin, http://www.cs.columbia.edu/~smb
