Hello, we have updated from Mikrotik 7.14.3 to 7.15.3. We have VLAN99 on the bridge and it has now received a new MAC address. Since we have reserved our IP addresses in the router, every device has now received a new IP.
Why does the MAC address of the bridge sometimes change? Or can this be improved?
When you create a new bridge, it will default to auto-mac=yes. Set
admin-mac=xx:xx:xx:xx:xx:xx auto-mac=no
to always keep the same.
Oh, so does that mean I always have to set one manually? Can I come up with some kind of MAC address or how do I make sure I don’t have a duplicate?
When auto-mac is enabled (yes) the behaviour of the Mikrotik is to give to the bridge the same address as one of the ports that are part of the bridge.
This is (should be) the first port added to the bridge, but it is susceptible to change when configuration changes, or even after a simple reboot in some cases:
http://forum.mikrotik.com/t/bridge-auto-mac-issue/162131/1
A recent related thread::
http://forum.mikrotik.com/t/script-for-setting-locally-administered-mac-address-on-bridges/177344/1
Read about Locally Adminiatered address (LAA) in article on MAC addresses. In short: take MAC address of ether1 and make the second digit from the left either 2, 6, A or E (which means you can construct 4 such MAC addresses out of every physical interface MAC address on each of your devices; unless you are very lucky they will be unique in your LAN).