Hi,
The Mikrotik community is so active that I could hardly believe that I would have something to add to its knowledge base. When searching for material on the RB1100 Ethernet Bypass functionality I noticed that there are relatively few references on it.
Ethernet Bypass is a functionality present in RB1100 series for many years, but I believe that it has not been given the publicity it reserved. This pushed me to publish the solution (the principle of it at least) I have implemented for a location where high availability of servers to the Internet is important.
At first, I would like to present a sketch of my own which would help those, who may not fully understand what is happening behind the scenes of the "Ethernet Bypass" feature.
https://drive.google.com/file/d/0B2Vw8J ... sp=sharing
Here we can see that as long as the Routerboard is powered on all ports including 11 & 12 behave normally. As soon as the power goes out and the Bypass Switch located before the two Bypass ports is enabled ("1"), the ports get interconnected. Therefore the two cables plugged into them become, electrically, a single cable connecting their two other edges. Eg. in case port 11 is connected to a server and the port 12 is connected to adsl router, the server, under these circumstances gets connected to the adsl router. Now we can see a real life application of this feature.
We have a rack space communicating with the Internet via two gateways using separate lines. Βoth lines are valuable because we implement load balancing. We also have two interconnected routers for redundancy. We wish the minimum possible impact by a router failure.
1. We connect each router to each gateway. That way if we lose a router we lose one line but we keep the other.
2. We connect the routers and the gateways on a switch. That way we keep both lines in case of router failure but we lose both lines in case of switch failure.
3. We use a pair of RB1100 as shown in this https://drive.google.com/file/d/0B2Vw8J ... sp=sharing
Using the last solution, when all devices are OK, the setup is like the first one. Bridge configuration and ports 12 interconnection assure that the routers and the gateways coexist all in the same ethernet network. As soon as a router experiences a power failure (and the bypass switch is enabled) its ports 11 & 12 will sort-circuit, connecting practically the port 12 of the other router to the gateway of the failed one.
This is, of course, just an approach ( an easy one ). In my case the use of VRRPs on 11-12 bridge ports were essential for accepting connections from the Internet, no matter which router is alive. Depending on the configuration, VRRPs might prove useful also for the LAN side.
Failover routing configuration between servers and Internet belong to a field well documented in Mikrotik and other Forums. If though there is interest for the RouterOS configuration of my solution I will try to minimize it and post it to a future post so as to be easily adoptable.
Hope I helped with promoting this feature which, in turn, would encourage Mikrotik to continue/expand the production of such models.

Thanks, this was a great post!

Yes, thank you very much for this great explanation.

As addition, I found a (very short descripted) old source for this: https://i.mt.lv/cdn/product_files/rb1100ug_130515.pdf

regards, DNAT

Since often a ISP modem/ONT has one port... the use case for the RB1100's "bypass" with VRRP and 2nd router is undervalued aspect of it. Or ISP gives use a subnet like a typical /29, to allow other routers so that even if the router is rebooted, those servers/routers use a public address for an ISP subnet still have access. It's unfortunate "bypass ports" are not on newer routers.