[PLUG] Lan loops - follow on PoE injecto

Russell Senior russell at personaltelco.net
Wed Dec 25 17:32:44 UTC 2019


Only one way to be sure! ;-)

On Wed, Dec 25, 2019 at 9:19 AM Mike C. <mconnors1 at gmail.com> wrote:

> >
> > 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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