Mikrotik - Loop Protect (loop-protect feature for ethernet,vlan,eoip,eoipv6 interfaces)

Loop protect feature can prevent Layer2 loops by sending loop protect protocol packets and shutting down interfaces in case they receive loop protect packets originated from themself. The feature works by checking source MAC address of received loop protect packet against MAC addresses of loop protect enabled interfaces. If the match is found, loop protect disables the interface which received the loop protect packet. Log message warns about this event and interface is marked with a loop protect comment by system. RouterOS loop protect feature can be used on bridged interfaces as well as on ethernet interfaces which are set for switching in RouterBoard switch chips.

Loop protect works on ethernet, vlan, eoip and eoipv6 interfaces. It supports adjusting loop protect packet sending interval and interface disable time. Configuration changes or expiration of disable time resets loop protection on interface. 

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fonte: http://www.itlearnweb.com/2016/10/loop-protect-loop-protect-feature-for.html