OSPF can be a canker to a network.
While working at a large ISP the fully meshed routers (using OSPF) decided to tell each other that the shortes path to anywhere was through themselves. So there we had it, a mesh of routers all telling each other "Psst.. the fastest route to anywhere outside of 127.0.0.1 is via 127.0.0.1, pass it on"

Always check that SPF rule..

Possibly the worst day of my life.....