Mixing OSPF interface network types.

So, curiously, and contrary to CCNP (R&S) knowledge, you can mix and match OSPF interface network types.

You need to pay attention to:

1) Timers
2) DR/BDR electiveness

For the first topic, quite self-explanatory. The timers must match. Hello and Dead interval, that was obvious.

For the second, not so easy. If the participant interfaces have the same DR/BDR electiveness type (ie, participate or not in DR/BDR elections) they will be compatible. That's broadcast and non-broadcast for DR/BDR elective; point-to-point, point-to-multipoint and point-to-multipoint non broadcast for not DR/BDR elective.

The not-so-easy part is that if the timers match and the DR/BDR electiveness is mismatch. The frakking things will establish the frakking adjacency! This drove me nuts for two days. TWO DAYS. But they won't exchange a frakking LSA.

Frak me.

(and I found a copy of John T. Moy's OSPF book. I should read it, I guess)