An OSPF router has learned a path to an external network by both an E1 and an E2 advertisement. Both routes have the same path cost. Which path will the router prefer?

Question

Options

• AThe router will use both paths equally utilizing ECMP.
• BBoth routes will be suppressed until the path conflict has been resolved.
• CThe router will prefer the E1 path.
• DThe router will prefer the E2 path.

• A
  6% (3)
• B
  4% (2)
• C
  77% (40)
• D
  13% (7)

Explanation

When an OSPF router receives both an E1 and E2 route to the same external destination with equal external costs, it always prefers E1 because E1 metrics accumulate the internal OSPF path cost to the ASBR plus the external cost - giving a more accurate end-to-end view of the path. E2 metrics, by contrast, reflect only the external cost assigned at the redistributing router and stay flat as they traverse the OSPF domain, making them less precise. OSPF's defined preference order is intra-area > inter-area > E1 > E2, so the tie-breaking rule is unambiguous.

Why the distractors are wrong:

• A (ECMP): Equal-cost multipath only kicks in when routes share the same type and metric; E1 and E2 are different route types, so OSPF resolves the tie by type preference rather than load-balancing.
• B (suppressed): OSPF does not suppress conflicting external routes - it has a well-defined preference hierarchy that handles this automatically.
• D (E2 preferred): E2 is actually the lower-preference type; its flat metric makes it less reliable for routing decisions than E1.

Memory tip: Think "E1 is #1" - because E1 adds internal costs to the metric, it tells the whole story of the path, so OSPF trusts it more and always picks it over E2 when both are present.

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