The answer is that the `bgp always-compare-med` command is missing, which prevents MED comparison between paths from different autonomous systems. By default, BGP only considers the Multi-Exit Discriminator (MED) attribute when comparing routes learned from the same AS; since R2 and R3 are in different ASes, the MED values of 200 and 100 are ignored entirely, and the best-path selection falls to the next tie-breaker—typically the IGP metric to the next-hop—which favors R3. This scenario directly tests your understanding of the BGP MED comparison only within same AS rule, a classic trap on the Cisco CCNP ENARSI 300-410 exam where engineers mistakenly assume that setting a lower MED on inbound routes will always make them preferred. The key takeaway: without `bgp always-compare-med`, MED is effectively dead for inter-AS comparisons. Memory tip: “MED is same-AS only—unless you always-compare.”
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. 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 attribute manipulation causes unexpected path selection. Router R1 and R2 are eBGP peers. R1 receives prefix 172.16.0.0/16 from R2 with MED 50 and from another peer R3 with MED 100. R1 has configuration: 'route-map SET-MED permit 10 set metric 200' applied to neighbor R2 inbound. R1 shows 'show ip bgp 172.16.0.0' output: 'BGP routing table entry for 172.16.0.0/16, version 2, Paths: (2 available, best #2) Path #1: from R2 with MED 200, Path #2: from R3 with MED 100'. The best path is via R3, but the network expects R2 to be preferred. What is the root cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'bgp always-compare-med' command is missing, causing MED to be ignored for paths from different ASes.
BGP best path selection uses MED only if paths are from the same AS (if 'bgp always-compare-med' is not configured). Since R2 and R3 are different ASes, MED is not compared; instead, the next tie-breaker (e.g., IGP metric to next-hop) selects R3. The route-map sets MED on R2's routes, but it does not affect the comparison because of AS path difference.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 'bgp always-compare-med' command is missing, causing MED to be ignored for paths from different ASes.
Why this is correct
Without this command, MED is only compared within same AS, so R2's lower MED (200 vs 100) is not considered, and R3's path is chosen.
Clue confirmation
The clue word "best" in the question point toward this answer.
The route-map SET-MED should be applied outbound on R2, not inbound.
Why it's wrong here
Inbound sets MED on received routes, which is correct.
✗
R2's next-hop is unreachable via IGP, causing R1 to ignore R2's path.
Why it's wrong here
Both paths are available.
✗
R1 has 'bgp bestpath med missing-as-worst' configured, causing missing MED to be treated as worst.
Why it's wrong here
MED is set, not missing.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The 'bgp always-compare-med' command is missing, causing MED to be ignored for paths from different ASes. — BGP best path selection uses MED only if paths are from the same AS (if 'bgp always-compare-med' is not configured). Since R2 and R3 are different ASes, MED is not compared; instead, the next tie-breaker (e.g., IGP metric to next-hop) selects R3. The route-map sets MED on R2's routes, but it does not affect the comparison because of AS path difference.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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