- A
The summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2.
summary-only causes all more specific routes to be suppressed, even if they are explicitly configured with network statements.
- B
The network 10.1.0.0/16 is not in the routing table of R1, so it cannot be advertised.
Why wrong: The network statement requires a matching route in the routing table, but the issue is suppression, not absence.
- C
R2 must have a route-map to accept the more specific route.
Why wrong: R2 does not filter inbound; the problem is on R1's outbound advertisement.
- D
The aggregate-address should be configured with the as-set keyword to include more specifics.
Why wrong: as-set affects AS_PATH, not suppression of more specifics.
Quick Answer
The answer is that the summary-only keyword is the root cause, as it suppresses all more specific routes from being advertised to BGP neighbors. When you configure the aggregate-address command with the summary-only option, BGP automatically filters out any more specific prefixes that fall within the aggregate range—including the explicitly networked 10.1.0.0/16—so only the summary 10.0.0.0/8 is sent to peers. This behavior is a classic trap on the Cisco CCNP ENARSI 300-410 exam, testing your understanding of how BGP route aggregation interacts with route suppression; many candidates mistakenly think a network statement overrides the aggregate, but summary-only takes precedence. To preserve the more specific routes for traffic engineering while still advertising the aggregate, you must either remove the summary-only keyword or use a route-map with the suppress-map option to selectively unsuppress certain prefixes. Remember the mnemonic: “Summary-only says ‘no details allowed’—if you want specifics, drop the keyword or use a map.”
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.
R1 and R2 are eBGP peers. R1 advertises a summary route 10.0.0.0/8 via aggregate-address 10.0.0.0 255.0.0.0 summary-only. R2 receives the summary but also expects to receive more specific routes (e.g., 10.1.0.0/16) for traffic engineering. R2's BGP table shows only the summary, and the more specific routes are missing. R1's configuration includes: router bgp 65001, network 10.1.0.0 mask 255.255.0.0, and aggregate-address 10.0.0.0 255.0.0.0 summary-only. 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 summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2.
The aggregate-address with summary-only suppresses all more specific routes from being advertised to neighbors. Even though the network 10.1.0.0/16 is injected into BGP, the summary-only keyword causes it to be suppressed from advertisements. To allow the more specific route to be advertised alongside the summary, the summary-only keyword should be removed, or the more specific route should be explicitly permitted via a route-map. The root cause is that summary-only suppresses the more specific routes.
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 summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2.
Why this is correct
summary-only causes all more specific routes to be suppressed, even if they are explicitly configured with network statements.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The network 10.1.0.0/16 is not in the routing table of R1, so it cannot be advertised.
Why it's wrong here
The network statement requires a matching route in the routing table, but the issue is suppression, not absence.
- ✗
R2 must have a route-map to accept the more specific route.
Why it's wrong here
R2 does not filter inbound; the problem is on R1's outbound advertisement.
- ✗
The aggregate-address should be configured with the as-set keyword to include more specifics.
Why it's wrong here
as-set affects AS_PATH, not suppression of more specifics.
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.
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 summary-only keyword suppresses all more specific routes, including the network 10.1.0.0/16, from being advertised to R2. — The aggregate-address with summary-only suppresses all more specific routes from being advertised to neighbors. Even though the network 10.1.0.0/16 is injected into BGP, the summary-only keyword causes it to be suppressed from advertisements. To allow the more specific route to be advertised alongside the summary, the summary-only keyword should be removed, or the more specific route should be explicitly permitted via a route-map. The root cause is that summary-only suppresses the more specific routes.
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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