The question I was asked about OSPF

At interview,
1. Does your OSPF router-id need to be a reachable IP address ?
The answer is NO.

2. Can we set 239.1.1.1 as OSPF router-id?
The answer is YES.

3. Cisco OSPF Network Types and RFC Network Types? :)
Non-Broadcast > RFC2328
Broadcast > Cisco
Point-to-Point > Cisco
Point-to-Multipoint > RFC2328
Point-to-Multipoint Non-Broadcast > Cisco

4. Is Area 1 equal to Area 1.1.1.1 ?
The answer is NO.
Area1 = Area 0.0.0.1
Area0 = Area 0.0.0.0