Hello Kevin,
if your firewalls are running OSPF on their own inside interface all you need to do is to setup appropriate static routes on the firewalls.
On FW1 you configure a static route for reaching the locally connected sharepoint router. Then you redistribute the static route(s) into OSPF.
The same can be done on FW2 at the secondary site
This requires the following:
- FW inside interfaces have to run OSPF
- FW inside interfaces have to be part of a standard OSPF area or a NSSA area.
Similarly you could do the same on internal routers connected to the FW inside interfaces, if your FW are not running OSPF. You would need a set of static routes for the sharepoint router on that internal router with next-hop the FW inside interface, and then to redistribute them into OSPF.
However, an issue is still open: if you don't control the sharepoint routers how to tell them of the backup path via your internal network?
If so you have to work with SP people to have them configure floating static routes pointing to your FW DMZ or outside interface address so that when the MPLS link fails they will use the path via your internal network.
I would not consider extending OSPF to the sharepoint routers as it means running OSPF on your DMZ/outside interface for security reasons.
In addition to routing both FWs need configuration to permit traffic from their DMZ/outside to inside between the sharepoint routers.
Hope to help
Giuseppe
