Re: RB750gr3, v6.48.6
I found an odd issue when Mikrotik auto assigns a mac address for bridge interface on Mikrotik routers. According to Mikrotik documentation (https://wiki.mikrotik.com/wiki/Manual:I ... face_Setup), the MAC address is chosen from the first added bridge port and after a reboot, the bridge MAC can change depending on the port-number. That second part is important, “the bridge MAC can change after reboot.”
In this scenario, I have two RB750 routers connected to each other through two WAP60ad’s serving as wireless bridges. For the sake of this discussion we will call the two routers Router-A and Router-B. Everything centers on the actions of Router-B.
Both routers are set up nearly identical with all ports in a single bridge. When I first configured Router-B, using a script that adds the bridge interface with auto-mac enabled, it assigned the MAC address of Ether1 to the bridge interface. That was as expected. The problem came in when I took it out and installed it in the field connected to Router-A through the wireless bridge.
After powering off Router-B and connecting it in the field, where it is now bridged with the two WAP60ad and Router-A, upon reboot the bridge interface for Router-B took on the MAC address of the bridge interface on Router-A.
At first I thought this was some odd fluke, so I full reset and reloaded the script, after which it came up with the correct MAC address (Ether1 of Router-B) as it had when I initially set it up. All well and good I thought, but after another reboot, the bridge once again reverted back to the “stolen” MAC address of Router-A.
Thinking that I might have something strange going on with this particular router, I tried changing out Router-B with another RB750, but the results were the same.
The solution was to set the MAC address for the bridge interface manually using “admin-mac=[Ether1-Mac]” and “auto-mac=no.” Now that the MAC address is set manually and it survives reboot without change. I guess this will be my default method for creating bridges going forward.