- A
The route-map SET_LOCAL_PREF is applied outbound instead of inbound, so it does not affect the received prefix.
If the route-map is applied outbound, it modifies routes sent to the neighbor, not received from it, so the local preference is not set.
- B
The MED value of 50 is lower than the default, causing it to be preferred over local preference.
Why wrong: Local preference is checked before MED in BGP path selection.
- C
The prefix is not being advertised by the neighbor with the higher local preference route-map.
Why wrong: The output shows the path exists; the issue is with the route-map application.
- D
The BGP table has a route from an iBGP peer with a lower IGP metric to the next-hop, overriding the local preference.
Why wrong: Local preference is compared before IGP metric to next-hop.
Quick Answer
The answer is that the route-map SET_LOCAL_PREF is misapplied outbound instead of inbound, so it never modifies the incoming prefix from neighbor 2001:DB8:1::2. BGP path selection begins by comparing local preference, where the highest value wins; since the route-map is applied outbound, it would only affect routes sent *to* that neighbor, not routes received *from* it, leaving the received prefix with the default local preference of 100. This explains why the path from 2001:DB8:2::2, which has a MED of 50, is selected—because after the local preference tie (both effectively 100), the path with the lower MED wins. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the critical difference between inbound and outbound route-map application, a common trap where engineers forget that "in" modifies incoming updates and "out" modifies outgoing updates. A simple memory tip: "In for Incoming, Out for Outgoing—always check the arrow direction."
300-410 IPv6 First Hop Security Practice Question
This 300-410 practice question tests your understanding of ipv6 first hop security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network engineer is troubleshooting IPv6 BGP path selection on Router R1. Router R1 is receiving a prefix from two different BGP peers, but it is not selecting the expected best path. Router R1 has the following relevant configuration:
router bgp 65000
address-family ipv6 unicast
neighbor 2001:DB8:1::2 route-map SET_LOCAL_PREF in neighbor 2001:DB8:2::2 route-map SET_MED in
! route-map SET_LOCAL_PREF permit 10 set local-preference 200 ! route-map SET_MED permit 10 set metric 50 !
Router R2 shows: show bgp ipv6 unicast 2001:DB8:3::/64 output indicates that the path from 2001:DB8:1::2 has local preference 200, but the path from 2001:DB8:2::2 is selected. 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 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
The route-map SET_LOCAL_PREF is applied outbound instead of inbound, so it does not affect the received prefix.
BGP path selection first compares local preference; the path with higher local preference should win. If the path with lower local preference is selected, there may be an issue with the route-map application or the neighbor configuration. The correct answer identifies that the route-map SET_LOCAL_PREF is not applied inbound to the correct neighbor, or the neighbor is not sending the prefix, causing the path with lower local preference to be the only path available.
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 route-map SET_LOCAL_PREF is applied outbound instead of inbound, so it does not affect the received prefix.
Why this is correct
If the route-map is applied outbound, it modifies routes sent to the neighbor, not received from it, so the local preference is not set.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The MED value of 50 is lower than the default, causing it to be preferred over local preference.
Why it's wrong here
Local preference is checked before MED in BGP path selection.
- ✗
The prefix is not being advertised by the neighbor with the higher local preference route-map.
Why it's wrong here
The output shows the path exists; the issue is with the route-map application.
- ✗
The BGP table has a route from an iBGP peer with a lower IGP metric to the next-hop, overriding the local preference.
Why it's wrong here
Local preference is compared before IGP metric to next-hop.
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.
Trap categories for this question
Command / output trap
The output shows the path exists; the issue is with the route-map application.
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.
What to study next
Got this wrong? Here's your next step.
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.
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 First Hop Security — This question tests IPv6 First Hop Security — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The route-map SET_LOCAL_PREF is applied outbound instead of inbound, so it does not affect the received prefix. — BGP path selection first compares local preference; the path with higher local preference should win. If the path with lower local preference is selected, there may be an issue with the route-map application or the neighbor configuration. The correct answer identifies that the route-map SET_LOCAL_PREF is not applied inbound to the correct neighbor, or the neighbor is not sending the prefix, causing the path with lower local preference to be the only path available.
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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Last reviewed: Jun 18, 2026
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