I have a working PPPoE Server running on a dedicated RouterBoard.  The Routerboard currently has a single working uplink to our 'core' router.

I would like to configure the PPPoE Server Router to have two uplinks (not one).  We use OSPF on the network to connect to "Core A" and "Core B".  Trouble is, in the PPPoE Server Router, under 'Local Address' I have the current uplink IP address entered (which works) - but when I configure two uplinks and OSPF, this Local Address is not necessarily valid due to the path OSPF selects (and should an uplink fail).  When this happens the PPPoE clients cannot connect to the Internet as a result.

Any suggestions on what I should do about the Local Address entry under the default PPP Profile?

Thank you

Not sure if I understood your scenario properly, but my suggestion would be to use something like 10.0.0.1 as "Local Address". Your PPPoE clients will get a PtP route to your PPPoE Server which they will reach through the tunnel (which can be encripted, etc). That 10.0.0.1 address will be the defeult route for your PPPoE Clients, so for your clients to reach Internet they will route through your PPPoE Server. Think of it as is the PPPoE Server was just another router...

From there, just set two routes on the PPPoE Server using your uplinks using whatever suits you best to share the load (http://wiki.mikrotik.com/wiki/Load_Balancing) and your clients will reach the Internet.

I would suggest using 2 PPPoE Servers, each with 2 default routes to both uplinks but only one active using different distances and check gateway. Make each PPPoE Server use a different uplink by default and you'll get decent redundancy.