Manual:Loop Protect

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Applies to RouterOS: v6.37+

Loop Protect

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 themselves. 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 and its packets are encapsulated with EtherType 0x9003.
There is support for adjusting loop protect packet sending interval and interface disable time. Configuration changes or expiration of disable time resets loop protection on interface.


Note: Even though loop-protect can work on interfaces that are added to a bridge, it is still recommended to use (R/M)STP rather than loop-protect since (R/M)STP is compatible with most switches STP variants provide much more configuration options to fine-tune your network.

Sub-menu: /interface ethernet /interface vlan /interface eoip /interface eoipv6


Property Description
loop-protect (on | off | default; Default: default) Enables or disables loop protect on selected interface. default works as turned off.
loop-protect-send-interval (time interval; Default: 5s) Sets how often loop protect packets are sent on selected interface.
loop-protect-disable-time (time interval | 0; Default: 5m) Sets how long selected interface is disabled when loop is detected. 0 - forever.

Read-only properties

Property Description
loop-protect-status (on | off | disable)
  • on - loop-protect feature is turned on, interface is sending and listening for loop protect packets
  • off - loop-protect feature is turned off
  • disable - loop-protect feature is turned on, interface has received loop protect packet and disabled itself to prevent loop

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