- A
The route-map SET-LOCAL-PREF is applied outbound on R1 instead of inbound on R2, so R2 does not receive the modified local preference.
Local preference is a well-known mandatory attribute that is not passed between ASes. If the route-map is applied outbound on R1, it sets local preference in R1's BGP table, but when the route is sent to R2, the local preference is reset to 100 (default) because it is not sent in eBGP updates. R2 sees the path via R1 with local pref 100, not 200.
- B
The prefix-list PREFER is missing a permit statement for 10.1.1.0/24.
Why wrong: If the prefix-list did not match, the route would not have local pref 200 in the show bgp output.
- C
The route via R3 has a lower MED value, overriding local preference.
Why wrong: Local preference is compared before MED, so even if MED is lower, the path with higher local pref should win.
- D
The route via R1 is not synchronized with IGP, causing it to be considered invalid.
Why wrong: BGP synchronization is disabled by default in modern IOS, and the route is shown in BGP table, so it is valid.
300-410 Route Maps and Route Filtering Practice Question
This 300-410 practice question tests your understanding of route maps and route filtering. 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 administrator is troubleshooting BGP path selection for a dual-homed enterprise. Router R1 (AS 65001) has the following configuration: route-map SET-LOCAL-PREF permit 10 match ip address prefix-list PREFER set local-preference 200. Router R2 (AS 65002) shows: 'show bgp ipv4 unicast 10.1.1.0' has two paths: one via R1 with local pref 200, and one via R3 with local pref 100. However, 'show ip route 10.1.1.0' on R2 shows the path via R3 is installed. What is the root cause?
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 on R1 instead of inbound on R2, so R2 does not receive the modified local preference.
BGP path selection compares local preference first, so the path with local pref 200 should be preferred. However, if the route-map SET-LOCAL-PREF is applied inbound on R2 from R1, but the prefix-list PREFER does not match the route (e.g., incorrect prefix or mask), then the local preference is not set, and the default local preference (100) applies. The show bgp output shows local pref 200 for the path via R1, which suggests the route-map is applied correctly, but the route may be received from R1 with a different attribute (e.g., a higher MED or longer AS path) that overrides local preference after the fact. Alternatively, if the route-map is applied outbound on R1, it would not affect R2's path selection. The root cause is that the route-map is applied on the wrong neighbor or direction.
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 on R1 instead of inbound on R2, so R2 does not receive the modified local preference.
Why this is correct
Local preference is a well-known mandatory attribute that is not passed between ASes. If the route-map is applied outbound on R1, it sets local preference in R1's BGP table, but when the route is sent to R2, the local preference is reset to 100 (default) because it is not sent in eBGP updates. R2 sees the path via R1 with local pref 100, not 200.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The prefix-list PREFER is missing a permit statement for 10.1.1.0/24.
Why it's wrong here
If the prefix-list did not match, the route would not have local pref 200 in the show bgp output.
- ✗
The route via R3 has a lower MED value, overriding local preference.
Why it's wrong here
Local preference is compared before MED, so even if MED is lower, the path with higher local pref should win.
- ✗
The route via R1 is not synchronized with IGP, causing it to be considered invalid.
Why it's wrong here
BGP synchronization is disabled by default in modern IOS, and the route is shown in BGP table, so it is valid.
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
If the prefix-list did not match, the route would not have local pref 200 in the show bgp output.
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?
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — 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 on R1 instead of inbound on R2, so R2 does not receive the modified local preference. — BGP path selection compares local preference first, so the path with local pref 200 should be preferred. However, if the route-map SET-LOCAL-PREF is applied inbound on R2 from R1, but the prefix-list PREFER does not match the route (e.g., incorrect prefix or mask), then the local preference is not set, and the default local preference (100) applies. The show bgp output shows local pref 200 for the path via R1, which suggests the route-map is applied correctly, but the route may be received from R1 with a different attribute (e.g., a higher MED or longer AS path) that overrides local preference after the fact. Alternatively, if the route-map is applied outbound on R1, it would not affect R2's path selection. The root cause is that the route-map is applied on the wrong neighbor or direction.
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.
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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