From the Mikrotik Newsletter:
In RouterOS v6rc3 and newer releases we have
added a wonderful new diagnostics feature –
ability to detect cable problems. For example, if
you have an apartment building with complicated
Ethernet wiring inside the walls or ceilings, and
you lose the link – previously, you would need
special equipment to pinpoint the location of
cable damage, before you open that wall, but
now – RouterOS will tell you these things:
• which cable pair is damaged
• at what length is the cable broken
• how is the cable broken – shorted or torn
This also works if the other end is simply
unplugged – in that case, simply the cable lenght
will be shown.
This works on SXT-G, RB711G, RB2011, RB750
series and other devices with the same switch
chips, and also the Cloud Core series devices.
Here is example output:
[admin@CCR] > interface ethernet monitor ether5
In the above example, cable is not shorted but
cut “open” at 4 meters lenght, all cable pairs
equally at same location.