I have a Mikrotik Routerboard 751-series and have the following set up:
ether1 - N/A
ether2 - for future use
ether3 - pppoe modem connection attached
ether4 & ether5: LAN
At present I have the option of ADSL and my pppoe wireless connection, with the option to switch by disabling the primary route, where the MikroTik will jump over to the next 0.0.0.0/0 route being the pppoe option.
I have tried here http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/Filter
but for some reason the unit doesn't seem to automatically roll over to the pppoe connection if ADSL goes down (waiting on my telco to sort out a messy intermittent line fault).
Any advice on how to approach this would be appreciated.