This 300-410 practice question tests your understanding of bgp troubleshooting. 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.
R1 and R2 are iBGP peers in AS 65001. R1 has: neighbor 10.1.1.2 route-reflector-client. R2 advertises a prefix 192.168.1.0/24 with next-hop 10.1.1.2. R3, another iBGP speaker not a client of R1, receives the prefix but the next-hop is unchanged (10.1.1.2) and R3 cannot reach it because 10.1.1.2 is not directly connected. R1 has no other configuration. 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
✓
R1 is missing the next-hop-self configuration for its non-client peer R3, so the next-hop remains R2, which is not reachable by R3.
When a route reflector reflects a route from a client to a non-client, it does not modify the next-hop attribute by default. The next-hop remains the original router (R2). If the non-client (R3) does not have a route to that next-hop, the prefix is considered unreachable. The fix is to use next-hop-self on the route reflector for non-client peers, or ensure reachability to the next-hop. The root cause is that R1 is not configured with neighbor 10.1.1.3 next-hop-self for the non-client peer.
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.
✓
R1 is missing the next-hop-self configuration for its non-client peer R3, so the next-hop remains R2, which is not reachable by R3.
Why this is correct
Route reflectors do not change next-hop for reflected routes; next-hop-self is needed on the reflector for non-clients.
R2 should have sent the route with next-hop-self to R1.
Why it's wrong here
R2 is the originator; it can set next-hop-self but that is not required.
✗
R3 is missing a static route to 10.1.1.2.
Why it's wrong here
While that could fix reachability, the root cause is the missing next-hop-self on R1 for R3.
✗
The route-reflector-client command should be applied on R2 instead.
Why it's wrong here
R1 is the route reflector; client is correct on R1 for R2.
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.
BGP Troubleshooting — This question tests BGP Troubleshooting — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: R1 is missing the next-hop-self configuration for its non-client peer R3, so the next-hop remains R2, which is not reachable by R3. — When a route reflector reflects a route from a client to a non-client, it does not modify the next-hop attribute by default. The next-hop remains the original router (R2). If the non-client (R3) does not have a route to that next-hop, the prefix is considered unreachable. The fix is to use next-hop-self on the route reflector for non-client peers, or ensure reachability to the next-hop. The root cause is that R1 is not configured with neighbor 10.1.1.3 next-hop-self for the non-client peer.
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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