Which two circumstances can prevent two routers from establishing an OSPF neighbor adjacency? (Choose two.)
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A. B. C. D. E.DE.
OSPF (Open Shortest Path First) is a routing protocol used to exchange routing information between routers in a network. In order for two routers to establish an OSPF neighbor adjacency, there are several requirements that need to be met.
The two circumstances that can prevent two routers from establishing an OSPF neighbor adjacency are:
A. Mismatched Autonomous System Numbers: OSPF routers within the same Autonomous System (AS) should have the same AS number configured. If the two routers have different AS numbers, they will not be able to form an OSPF neighbor adjacency.
C. Mismatched Process IDs: OSPF routers within the same AS should have the same Process ID configured. If the two routers have different Process IDs, they will not be able to form an OSPF neighbor adjacency.
Explanation of other options:
B. An ACL blocking traffic from multicast address 224.0.0.10: OSPF uses multicast address 224.0.0.10 to send OSPF hello messages. If an Access Control List (ACL) is blocking traffic to this multicast address, the routers will not be able to form an OSPF neighbor adjacency.
D. Mismatched hello timers and dead timers: OSPF routers use hello messages to discover neighboring routers and establish a neighbor adjacency. Hello messages are sent at regular intervals, and if the timers are not synchronized between the two routers, they will not be able to form an OSPF neighbor adjacency.
E. Use of the same router ID on both devices: OSPF routers use a unique router ID to identify themselves. If two routers in the same OSPF domain have the same router ID, they will not be able to form an OSPF neighbor adjacency.