CCNA: Cisco Certified Network Associate — Question 128

Which two circumstances can prevent two routers from establishing an OSPF neighbor adjacency? (Choose two.)

Answer options

• A. mismatched autonomous system numbers
• B. an ACL blocking traffic from multicast address 224.0.0.10
• C. mismatched process IDs
• D. mismatched hello timers and dead timers
• E. use of the same router ID on both devices

Correct answer: D, E

Explanation

The correct answers are D and E because OSPF requires matching hello and dead timers to form adjacencies, and routers must have unique router IDs. The other options may affect OSPF operation but do not directly prevent the establishment of a neighbor adjacency.