- A
By default, the aggregate route is advertised with the ATOMIC_AGGREGATE attribute set.
Correct. When an aggregate is created, BGP sets the ATOMIC_AGGREGATE attribute to indicate that the path information might be incomplete.
- B
The 'aggregate-address' command automatically suppresses the advertisement of all more specific routes.
Why wrong: Incorrect. By default, the more specific routes are still advertised. The 'summary-only' keyword is required to suppress them.
- C
The aggregate route inherits the AS_PATH of the longest matching more specific route.
Why wrong: Incorrect. The aggregate route does not automatically inherit an AS_PATH; the 'as-set' keyword is needed to include the AS_PATH information from the component routes.
- D
The 'aggregate-address' command can be used to summarize both IPv4 and IPv6 prefixes in the same configuration.
Why wrong: Incorrect. The 'aggregate-address' command is address-family specific; you must configure it under the appropriate IPv4 or IPv6 address family.
- E
The aggregate route is installed in the BGP table only if at least one more specific route exists in the BGP table.
Correct. BGP creates the aggregate only when there is at least one more specific route in the BGP table that falls within the aggregate prefix.
Quick Answer
The correct answer is that the aggregate route is installed in the BGP table only if at least one more specific route exists in the BGP table. This behavior occurs because BGP route summarization using the aggregate-address command does not create the summary out of thin air; it requires a contributing component route in the BGP table to trigger the aggregate, ensuring the summary is based on real reachability. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how the aggregate-address command interacts with the BGP table and the optional keywords like summary-only and as-set. A common trap is assuming the aggregate automatically suppresses the more specific routes—it does not unless you explicitly add the summary-only keyword. Remember the memory tip: “No component, no aggregate—the summary needs a seed to grow.”
300-410 Route Summarization Practice Question
This 300-410 practice question tests your understanding of route summarization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which TWO statements correctly describe the behavior of BGP route summarization using the 'aggregate-address' command? (Choose TWO.)
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
By default, the aggregate route is advertised with the ATOMIC_AGGREGATE attribute set.
The BGP 'aggregate-address' command creates a summary route in the BGP table. By default, the summary is advertised with the ATOMIC_AGGREGATE attribute and the aggregator router ID, but the more specific routes are still advertised unless the 'summary-only' keyword is used. The summary inherits the AS_PATH from the component routes, but the 'as-set' keyword is required to include the AS_PATH information in the aggregate. The summary does not automatically suppress the component 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.
- ✓
By default, the aggregate route is advertised with the ATOMIC_AGGREGATE attribute set.
- ✗
The 'aggregate-address' command automatically suppresses the advertisement of all more specific routes.
Why it's wrong here
Incorrect. By default, the more specific routes are still advertised. The 'summary-only' keyword is required to suppress them.
- ✗
The aggregate route inherits the AS_PATH of the longest matching more specific route.
Why it's wrong here
Incorrect. The aggregate route does not automatically inherit an AS_PATH; the 'as-set' keyword is needed to include the AS_PATH information from the component routes.
- ✗
The 'aggregate-address' command can be used to summarize both IPv4 and IPv6 prefixes in the same configuration.
Why it's wrong here
Incorrect. The 'aggregate-address' command is address-family specific; you must configure it under the appropriate IPv4 or IPv6 address family.
- ✓
The aggregate route is installed in the BGP table only if at least one more specific route exists in the BGP table.
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
Keyword trap
Incorrect. By default, the more specific routes are still advertised. The 'summary-only' keyword is required to suppress them.
Command / output trap
Incorrect. The 'aggregate-address' command is address-family specific; you must configure it under the appropriate IPv4 or IPv6 address family.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 Summarization — This question tests Route Summarization — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: By default, the aggregate route is advertised with the ATOMIC_AGGREGATE attribute set. — The BGP 'aggregate-address' command creates a summary route in the BGP table. By default, the summary is advertised with the ATOMIC_AGGREGATE attribute and the aggregator router ID, but the more specific routes are still advertised unless the 'summary-only' keyword is used. The summary inherits the AS_PATH from the component routes, but the 'as-set' keyword is required to include the AS_PATH information in the aggregate. The summary does not automatically suppress the component 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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