What could be the cause of this problem?

You have completed an OSPF implementation, and you are verifying OSPF operation. During this
verification, you notice that the OSPF route of 172.16.10.0 is repeatedly appearing and
disappearing from the routing table. Further investigation finds that the OSPF CPU utilization is
very high and the routers are constantly performing SPF calculations. You determine that
172.16.20.2 is the source of the 172.16.10.0 route. Using the show ip ospf database router
172.16.20.1 command, you notice that when this show command is performed repeatedly, the
contents of the LSA change every few seconds.
What could be the cause of this problem?

A.
OSPF authentication errors between some of the routers.

B.
Two routers have the same OSPF router ID.

C.
Issues with mistuned OSPF timers.

D.
OSPF LSA pacing issues between some of the routers.

E.
OSPF neighbor adjacency problems between some of the routers.

Explanation:
When two routers use the same router ID in an OSPF domain, routing possibly does not work

correctly. Cisco bug IDs CSCdr61598 and CSCdu08678 enhance the detection and reporting
mechanisms of duplicate router IDs. Access the Bug Toolkit (registered customers only) in order to
view additional information about these Cisco bug ID.
Reference:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080117102.shtml