OSPF default operation varies dependent upon the type of interface it is connected to.
When enabled on a serial interface running either PPP or HDLC encapsulation (or P2P subinterface running frame-relay or ATM), it will infer a P2P topology and demonstrate the following characteristics:
- Will not elect DR or BDR (as it assumes two neighbors only)
- Still sends all OSPF hello packets to multicast 224.0.0.5
The default hello and dead timers are 10 and 40 seconds, respectively.
Stuck-in-Active: Journal of an IT-Network Administrator 