[126374] in North American Network Operators' Group
Re: POE switches and lightning
daemon@ATHENA.MIT.EDU (Daniel Senie)
Thu May 13 14:24:26 2010
From: Daniel Senie <dts@senie.com>
In-Reply-To: <4BEC2B2E.4030501@altadena.net>
Date: Thu, 13 May 2010 14:24:04 -0400
To: Pete Carah <pete@altadena.net>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
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.
On May 13, 2010, at 12:39 PM, Pete Carah wrote:
> On 05/13/2010 12:19 PM, Larry Sheldon wrote:
>> On 5/13/2010 10:36, Caleb Tennis wrote:
>>=20
>>> We had a lightning strike nearby yesterday that looks to have come =
inside our facility via a feeder circuit that goes outdoors underground =
to our facility's gate. =20
>>>=20
>>> What's interesting is that various POE switches throughout the =
entire building seemed to be affected in that some of their ports they =
just shut down/off. Rebooting these switches brought everything back to =
life. It didn't impact anything non-POE, and even then, only impacted =
some devices. But it was spread across the whole building, across =
multiple switches.
>>>=20
>>> I was just curious if anyone had seen anything similar to this =
before? Our incoming electrical power has surge suppression, and the =
power to the switches is all through double conversion UPS, so I'm not =
quite sure why any of them would have been impacted at all. I'm =
guessing that the strike had some impact on the electrical ground, but I =
don't know what we can do to prevent future strikes from causing the =
same issues. Thoughts?
>>>=20
>>=20
>> I don't know how to account for this in a PoE world, but when I last
>> managed a campus network, we had major issues (particularly in an
>> active-thunder-storm environment) of severe difference in
>> ground-potential between buildings.
>>=20
> Cat 5 has isolation transformers in or just behind each jack. =
However,
> in most equipment the grounds aren't really isolated, and in the case =
of
> POE they (mostly) aren't at all.
>=20
> Lightning likes to do "interesting" things. It can induce a 20kv per
> few feet gradient (or more) across the ground mesh of a power =
substation
> (like 4/0 wire in a mesh of 4 foot squares or so; normally more
> complicated than that since it has to clear equipment etc...). It =
likes
> to eat power supplies in well-grounded equipment and leave cheaper =
stuff
> alone. It can hit an antenna, leave the receiver completely intact, =
and
> fry the power supply of the next box over. We tended to lose either
> fluorescent ballasts or the thermostat transformer in our furnace when =
I
> lived in an active ham's house in Alabama, the radios tended to live.=20=
> (you should have seen his coax entry panel (1/4 inch copper sheet,
> grounded outside)), and stuff got manually disconnected from both
> antennas and power when a storm was expected (every afternoon :-).
>=20
> It wouldn't surprise me if the first answer was right and either the
> ground pulse or EMP reset the safety switches in the POE feeders.
>=20
> -- Pete
>=20
