- A
The router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement.
With synchronization enabled, the router checks the IGP for the prefix. If missing, the route is not advertised to eBGP.
- B
The router has 'bgp bestpath as-path multipath-relax' configured, which suppresses eBGP advertisements for iBGP routes.
Why wrong: This command affects multipath, not synchronization or advertisement.
- C
The iBGP session is not using 'next-hop-self', so the next hop is unreachable.
Why wrong: Next-hop-self affects reachability, but synchronization is a separate check.
- D
The router has 'bgp suppress-duplicates' enabled, which drops identical routes.
Why wrong: This is not a valid BGP command.
Quick Answer
The answer is that the router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement. This occurs because BGP synchronization mandates that an iBGP-learned route must also be present in the IGP—such as OSPF—before the router will advertise it to eBGP neighbors. If the IGP does not carry the route, the router suppresses the advertisement even though the route exists in the BGP table, effectively breaking transit traffic flow. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the synchronization rule’s purpose: preventing black-hole routing when routers in the same AS are not fully meshed. A common trap is assuming that a valid BGP table entry alone guarantees advertisement to eBGP peers. Remember the memory tip: “Sync before you send—if the IGP doesn’t know, the eBGP won’t go.”
300-410 BGP Troubleshooting Practice Question
This 300-410 practice question tests your understanding of bgp troubleshooting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 configures BGP synchronization on an iBGP router. The IGP (OSPF) does not carry the BGP routes. Unexpectedly, the router does not advertise these iBGP routes to eBGP neighbors. What is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement.
BGP synchronization requires that an iBGP route must be present in the IGP before it can be advertised to eBGP neighbors. If the IGP does not carry the route, the router will not advertise it, even if it is in the BGP table.
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 router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement.
- ✗
The router has 'bgp bestpath as-path multipath-relax' configured, which suppresses eBGP advertisements for iBGP routes.
Why it's wrong here
This command affects multipath, not synchronization or advertisement.
- ✗
The iBGP session is not using 'next-hop-self', so the next hop is unreachable.
Why it's wrong here
Next-hop-self affects reachability, but synchronization is a separate check.
- ✗
The router has 'bgp suppress-duplicates' enabled, which drops identical routes.
Why it's wrong here
This is not a valid BGP command.
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
This command affects multipath, not synchronization or advertisement.
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?
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: The router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement. — BGP synchronization requires that an iBGP route must be present in the IGP before it can be advertised to eBGP neighbors. If the IGP does not carry the route, the router will not advertise it, even if it is in the BGP table.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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