Hello Peter,

That is exactly what I'm observing and it is making sense, but I've found it curios because everything I've read on OSPF didn't mention that.

Here is the chain of events, to be clear for anyyone that reads this post:

R1 - serial interface - IP: 1.1.1.1 <====FR SWITCH====> R2 - serial interface -IP: 1.1.1.2

*Jan 26 21:26:58.407: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

*Jan 26 21:26:58.535: OSPF: Rcv hello from 1.1.1.2 area 0 from Serial1/1 1.1.1.2

*Jan 26 21:26:58.543: OSPF: Send immediate hello to nbr 1.1.1.2, src address 1.1.1.2, on Serial1/1

*Jan 26 21:26:58.547: OSPF: Send hello to 1.1.1.2 area 0 on Serial1/1 from 1.1.1.1

*Jan 26 21:26:58.547: OSPF: End of hello processing

R1(config-if)#

*Jan 26 21:26:58.611: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.2 on Serial1/1 from LOADING to FULL, Loading Done

R1(config-if)#

*Jan 26 21:27:08.411: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

R1(config-if)#

*Jan 26 21:27:18.415: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

R1(config-if)#

*Jan 26 21:27:28.419: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

R1(config-if)#

*Jan 26 21:27:38.423: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

R1(config-if)#

*Jan 26 21:27:43.915: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.2 on Serial1/1 from FULL to DOWN, Neighbor Down: Dead timer expired

R1(config-if)#

*Jan 26 21:27:48.427: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

*Jan 26 21:27:48.479: OSPF: Rcv hello from 1.1.1.2 area 0 from Serial1/1 1.1.1.2

*Jan 26 21:27:48.483: OSPF: Send immediate hello to nbr 1.1.1.2, src address 1.1.1.2, on Serial1/1

*Jan 26 21:27:48.487: OSPF: Send hello to 1.1.1.2 area 0 on Serial1/1 from 1.1.1.1

*Jan 26 21:27:48.491: OSPF: End of hello processing

R1(config-if)#

*Jan 26 21:27:48.583: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.2 on Serial1/1 from LOADING to FULL, Loading Done

R1(config-if)#

*Jan 26 21:27:58.431: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.1

R2(config-if)#

*Jan 26 21:26:58.567: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:26:58.571: OSPF: Send immediate hello to nbr 1.1.1.1, src address 1.1.1.1, on Serial1/1

*Jan 26 21:26:58.575: OSPF: Send hello to 1.1.1.1 area 0 on Serial1/1 from 1.1.1.2

*Jan 26 21:26:58.579: OSPF: End of hello processing

*Jan 26 21:26:58.675: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:26:58.679: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:26:58.739: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial1/1 from LOADING to FULL, Loading Done

R2(config-if)#

*Jan 26 21:27:00.435: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:08.571: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:08.575: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:27:10.439: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:18.563: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:18.567: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:27:20.443: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:28.567: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:28.571: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:27:30.447: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:38.591: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:38.595: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:27:40.451: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:48.551: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:48.555: OSPF: Send immediate hello to nbr 1.1.1.1, src address 1.1.1.1, on Serial1/1

*Jan 26 21:27:48.559: OSPF: Send hello to 1.1.1.1 area 0 on Serial1/1 from 1.1.1.2

*Jan 26 21:27:48.563: OSPF: End of hello processing

*Jan 26 21:27:48.611: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:48.619: OSPF: End of hello processing

R2(config-if)#

*Jan 26 21:27:48.719: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial1/1 from LOADING to FULL, Loading Done

R2(config-if)#

*Jan 26 21:27:50.455: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 1.1.1.2

R2(config-if)#

*Jan 26 21:27:58.547: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial1/1 1.1.1.1

*Jan 26 21:27:58.547: OSPF: End of hello processing

Thank you Peter for your support !