Why is it necessary to create adjacency of OSPF neighbors on primary IPs only?
I have a ptp network type of OSPF & adjacencies cannot build on using secondary IPs. Is there any way around?
I am a bit puzzled why you would configure a secondary address on a serial link and then want to form the OSPF adjacency on the secondary and not the primary. But that is a side issue to your primary question.
You ask a valid question and it deserves an answer about why OSPF will only form adjacency on the primary address. And the answer is that the router always uses the primary address as the source address in the hello packets. So if your router sends a hello packet with source address of the primary in subnet 10.0.0.0 to a router that wants to use the secondary in 10.0.0.4 then they are not in the same subnet and will not form adjacency.