Hi ITPro, I just experienced a strange issue with OSPF in the field and thought I would run it by you. This isn't Cisco gear.. Basically we had two primary links fail between Site 1 and Site 4 (See diagram), and all other links have the same cost.
The Site 1 firewall chose a route to Site 2 for Site 4 access. (Site1>Site2>Site4) 800 total cost
The Site 4 firewall chose a route to site 3 for Site 1 access. (Site4>Site3>Site1) 800 total cost
Because the return route for traffic was different, in this scenario the packets were being dropped. I can't think of a way around this issue without manually adjusting the cost values so that the most preferred path would be uses and there wouldn't be a tie like this.
I am surprised that OSPF would do this, sharing the link state database across all routers I assumed would cause the same failover route selection regardless of more than one link combination using the same cost.