Derek Smithies wrote, On 20/01/14 19:21:
> p.s. I was hoping someone would add to this thread some more tech
> stories.... - hopefully those that involve linux.. 

Orright...

Once upon a time, I had a m0n0wall firewall in my garage.   It had a LAN
interface, a WAN interface to TCL cable, and a 802.11b wireless NIC,
unused but it was there.

For some reason, the home network ran really slow occasionally, only in
the day and unpredictably.  Then the problem would self-resolve.

I had an access point inside the house, about 15 metres away through the
tin garage and through the house walls.  The switch would have been an
unmanaged 100 Mbit AT at the time.

Turns out that when the garage door was open, the wireless NIC could see
the AP and connected, forming an ethernet loop, so at some point a
packet did the circle then created a packet storm.   The unmanaged
switch didn't have the smarts to run spanning tree to stop the problem.

Close the garage door and the second link was broken, no more loop.

Spotting the correlation took ages, because a packet storm only starts
when something broadcasts on all switch ports, AND the reply comes
around the loop.

The fix?  Change the wireless NIC's config so its no longer a client of
the AP... simple.



-- 
Criggie

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