The answer is that the MED is only compared when paths originate from the same neighboring AS, which is why the path with MED 50 is not preferred. This is because BGP’s Multi-Exit Discriminator is a non-transitive attribute designed to influence inbound traffic between multiple entry points of a single neighboring AS; when competing routes come from different neighboring ASes, the MED values are not comparable and are ignored for path selection. On the Cisco CCNP ENARSI 300-410 exam, this concept frequently appears as a trap where candidates assume a lower MED always wins, but the rule is strictly scoped to same-AS comparisons. A common memory tip is to think of MED as an “internal vote” within one AS—it has no weight when judging between different AS neighbors.
300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Option C is correct because 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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
MED is an optional non-transitive attribute defined in RFC 4271, meaning it is not passed to other ASes and is only compared when the paths have the same neighboring AS (the AS immediately before the current router). In BGP path selection, MED is compared after weight, local preference, and AS-path length; if the competing paths come from different neighboring ASes, MED is ignored entirely, and the decision moves to the next step (e.g., IGP metric or router ID). A real-world scenario is a multi-homed enterprise where MED is used to prefer one ISP link over another, but only if both links connect to the same ISP AS.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: MED is only compared when paths are from the same neighboring AS. — Option C is correct because 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.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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