[PLUG] Lan loops - follow on PoE injecto

Mike C. mconnors1 at gmail.com
Wed Dec 25 17:15:14 UTC 2019


>
> I happened to have a netgear FS105 nearby. Plugging in a laptop to a switch
> port, and plugging a patch cable between two other switch ports and pinging
> a random ip address from the laptop set off the broadcast storm. Running
> tcpdump from the laptop showed a bunch of "MPCP, Opcode Pause, length 46"
> packets. Unplugging the loop, the packets stop immediately.
>

The reason this works and why I suspect it won't work on the OPs router is
the Netgear isn't a 802.1D (Spanning Tree Compliant) switch. Those
multicast packets are flow control packets and would not be forwarded out
all switch ports downstream as per 802.1D they're reserved to be acted upon
only by the switch.



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