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300-410 BGP is used between two ISPs Practice Question

BGP is used between two ISPs. Router R1 has: neighbor 10.0.0.2 route-map SET-MED in, route-map SET-MED permit 10, set metric 50. Router R2 shows: show ip bgp 172.16.0.0 includes MED 50 but the path is not preferred. What is the root cause?

⚠ Common exam trap

Cisco often tests the nuance that MED is only compared between paths from the same neighboring AS, leading candidates to mistakenly think MED always influences path selection or that the value itself is the issue.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

MED is only compared when paths are from the same neighboring AS.

BGP's MED (Multi-Exit Discriminator) attribute is only compared between paths that originate from the same neighboring AS. In this scenario, even though R2 receives a route with MED 50 from R1, the path is not preferred because the competing path likely comes from a different neighboring AS, making the MED comparison invalid. MED is a non-transitive attribute that influences inbound traffic only when comparing multiple exit points from the same AS.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The MED value is too low to influence path selection.

    Why it's wrong here

    MED is compared only among same AS paths.

  • The route-map should be applied outbound, not inbound.

    Why it's wrong here

    Inbound route-map sets MED on received routes.

  • MED is only compared when paths are from the same neighboring AS.

    Why this is correct

    BGP default behavior ignores MED from different ASes.

  • The neighbor has a higher local preference overriding MED.

    Why it's wrong here

    Local preference is considered before MED, but the issue is MED comparison scope.

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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