Which three conditions are required for two FortiGate devices to form an OSPF adjacency?

The correct answers are C, D, and E.

The study guide lists the exact OSPF adjacency requirements:

“Interfaces of peers are the same type and in the same OSPF area”

“Each peer has a unique router ID”

“OSPF authentication, if enabled, is successful”

These map directly to:

C. OSPF interface network types match

D. Authentication settings match

E. OSPF router IDs are unique

The same study-guide slide also states other requirements such as:

peers’ primary IPs must be in the same subnet with the same mask

hello and dead intervals must match

OSPF MTUs must match

Why the other options are wrong:

A is wrong because link cost matching is not listed as an adjacency requirement. OSPF cost affects path selection, not whether adjacency can form.

B is wrong because interface priority does not need to be unique. Priority is used for DR/BDR election, where the highest priority wins, and ties are broken by router ID.

So the verified answers are: C, D, E.