Route redistribution and the loops it creates
Two protocols feeding each other at two points will create a loop. Here is how to stop it.
Writing
ospf
When OSPF neighbours will not form
The adjacency state tells you which check failed. Work the list in order.
OSPF cost and the traffic taking the wrong path
Traffic prefers a slow link over a fast one. The cause is usually a default reference bandwidth.
OSPF areas and why the design matters
Areas are not organisational tidiness. They control how much work every router has to do.