PoE, Comcast Modems, and Service Outages

Joe Greco jgreco at ns.sol.net
Tue Mar 29 21:00:05 UTC 2022

On Tue, Mar 29, 2022 at 03:07:47PM -0400, Josh Luthman wrote:
> We've routinely seen where lines not even connected to the same circuit in
> any way (ie an OTA antenna coax line and cat5 POE) cause issues with one
> another.  As much as we would all love to have a perfect line in the sand,
> there isn't.  Don't rule anything out until the issue is resolved.
> As someone that sees this in the field and watches people simply hate on
> someone because there's a frustrating situation, it's worth taking a breath
> before too upset.

You can run cable lines next to A/C wiring and get problems too.  Or
ethernet lines next to A/C wiring.  That does not justify wild claims
about PoE such as what this tech was making, and until someone shows
me a graph of "PoE buildups" observable via SNMP or whatever the
cable company is using to graph trends, it seems pretty clear that
this is a bogus answer.

There's a lot of difference between "we observed this very specific kind
of interference related to PoE in a particular circumstance" and the
crazy generalizations being made by the tech.  Asking to please make sure
your switch is grounded properly?  That'd be good.  Asking for PoE to be
disabled on the port?  Yeah fine.  Suggesting separation of cables? 
Sure.  Checking for proper grounding of the ground block (on the cable
inlet)?  Sure.  There's room for things to happen.

I'm all for investigating with an open mind, but I draw the line at crazy.

Given that so much of the world works on PoE, it seems like the other
potential resolution would be to note that there's an implication here
by the tech that Comcast's hardware is standards noncompliant and ask
them what they plan to replace their cheap CPE with.

... JG
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"The strain of anti-intellectualism has been a constant thread winding its way
through our political and cultural life, nurtured by the false notion that
democracy means that 'my ignorance is just as good as your knowledge.'"-Asimov

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