Here is an exert from Aaron’s OSPF Story:
Right in the middle of the config, I see “area 50 nssa”. Yes, this single non-backbone area with no real costs being advertised was configured as a not-so-stubby area. Not only did they go out of their way to make it a non-backbone area but they also wanted it as a stub area. Since they had all the other networks redistributing into the area, they had to make it NSSA. It’s a week later, and I still roll my eyes.
I’ve never seen a configuration like this before. Crazy.