Okay I've read too much and my brain is barfing...
This is simple and I should know it but every thing I read is slightly different. Mainly because not every thing I read is comprehensive, each puts in the points they think most important. So I've tried to compile a complete list...
When forming a neighbor relationship using OSPF the following must be true:
1) same area
2) same subnet and mask
3) timers must match (hello and dead)
4) mtu must match
5) stub flag must match
is there anything else? anything here that shouldn't be? I've tried in my lab and this seems to be true but, if I had left something out then I would also not know to try that in the lab so my answer would still be incomplete.
I passed that for the CCNA but the test was pretty breezy compared to what I would expect on CCNP. When trying to debug a failed relationship I want to be sure to check everything.