On an OSPF network, if two routers with the same router ID run in different areas and one of the routers is an ASBR, LSA flapping occurs.

Question

Options

• ATRUE
• BFALSE
• C
• D

• A
  83% (58)
• B
  4% (3)
• C
  3% (2)
• D
  10% (7)

Explanation

Option A is correct because OSPF router IDs must be unique across the entire OSPF autonomous system, not just within a single area. When two routers share the same router ID, their LSAs conflict because LSAs are identified by the combination of LS type, Link State ID, and the advertising router's ID. The situation is made worse by an ASBR, because Type 5 LSAs (external routes) are flooded domain-wide across all areas, meaning the duplicate ID causes widespread LSA conflicts and continuous re-origination, which is the definition of LSA flapping.

Option B is incorrect because the presence of a duplicate router ID is a well-documented OSPF instability trigger regardless of area boundaries, and the involvement of an ASBR amplifies the problem by spreading conflicting LSAs throughout the entire domain rather than containing them locally.

Options C and D are empty distractors and do not represent valid answers.

Memory tip: Think of an OSPF router ID like a passport number - it must be globally unique, not just unique within your home country (area). An ASBR acts like an international traveler whose conflicting passport causes problems everywhere it goes, not just at home.

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