Also possibly helpful explanation here: https://en.wikipedia.org/wiki/Switching_loop
Probably the best way to demonstrate this would be with a >=4 port unmanaged switch with two client devices and a loop: A----port1 port2----port3 port4----B where A and B are client devices and ---- are ethernet connections. ping between A and B. Connect and disconnect the ethernet between port2 and port3. Observe packet loss and/or a bunch of furiously flashing activity LEDs on the switch. On Tue, Dec 24, 2019 at 1:52 PM Mike C. <[email protected]> wrote: > The router/switch looks this way: > - WAN (eth0) > +- LAN1 (eth1) > +- LAN2 (eth2) > +- WLAN3 (wlan0) > > The easiest way is to get an old hub / bridge from Free Geek, Goodwill, etc > > for a $1 and connect it via to Eth1 & Eth2 of the sw/rtr. Viola you have > a > > LAN loop! > > > > I suspect the Openwrt sw/rtr will disable one of the eth ports down pretty > quickly via some version of spanning tree protocol and put a quick end to > your lil' science experiment. > > LAN loops were far more common back in the day of hubs & bridges and the > more haphazard way LANs were thrown together. Also, all the ports on hubs & > bridges share the same mac address and as you connect them together not > only do you expand the collision & broadcast domain but you potentially > create more than 1 communication path to end devices. FUN! > > Probably the most famous story of LAN loop is the spanning tree protocol > network failure at Beth Israel Deconess hospital. I know about his story > because when it happened I was a "young" Network Engineer newly hired by > Nortel Networks attending training in Billerica, MA. I learned all about > this problem and Nortel's network architecture and technologies to avoid > this type of catastrophic failure. > > For your reading pleasure and edification. > https://www.computerworld.com/article/2581420/all-systems-down.html > > Happy Holidays!, > > -- Mike > _______________________________________________ > PLUG mailing list > [email protected] > http://lists.pdxlinux.org/mailman/listinfo/plug > _______________________________________________ PLUG mailing list [email protected] http://lists.pdxlinux.org/mailman/listinfo/plug
