What is the “ethernet bypass” option on RB1100?
How can it be used in real life?
Thank you
Cannot find anything in the Mikrotik Manual, but ‘bypass mode’ usually means the interfaces are connected at the physical Layer 1 level.
I saw this on our RB1100. Never tried.
I think that a relay is physically connecting wires 1 to 8 (layer 1) between the two ports if power is dropped on the router.
Then removing power with a Power Control device you can get back connectivity to an urgency box.
This is a radical and simple solution, but efficient. This can be extended to multiple ports or even all ports using an external relay box.
I’ve often seen high tech and high cost High availability solutions miserabily fail at the first outage. The hardware bypass solution almost never fail to work !
That is the way it is done on other equipment, especially useful if the equipment can be temporarily disabled on power failure, with no serious detrimental effect on the traffic. For example if it is a traffic shaper, and it fails, all you lose is the shaping, you do not lose customers. Or gain angry customers! 
But how this works - is not documented. Therefore this is all theoretical until MT updates the wiki. 
You can take a look at this:
http://forum.mikrotik.com/t/rb1100-bypass-ports-application-example/96576/1