The answer is that the `summary-only` keyword in the `aggregate-address` command suppresses all more specific routes, including 10.0.3.0/24, from being advertised into BGP. This keyword tells BGP to advertise only the aggregate prefix (10.0.0.0/22) and to withhold any component prefixes that fall within that range, which is why the specific /24 is missing from the BGP table and unreachable from the MPLS core. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of BGP route summarization behavior in an MPLS VPN context, where the `summary-only` option is a common trap—candidates often forget that it removes the specific routes entirely, not just aggregates them. A reliable memory tip is to think of `summary-only` as “summary-only, specifics gone”—if you need the specific routes for traffic engineering or next-hop validation, omit this keyword or use `suppress-map` to selectively control which specifics are suppressed.
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Route summarization blocks specific routes in an MPLS network. Router R1 is a PE router that summarizes routes from a VRF into BGP. Configuration: 'router bgp 65000 address-family ipv4 vrf CUSTOMER network 10.0.0.0 255.255.252.0' and 'aggregate-address 10.0.0.0 255.255.252.0 summary-only'. A specific prefix 10.0.3.0/24 is not reachable from the MPLS core. 'show ip bgp vpnv4 vrf CUSTOMER 10.0.3.0/24' output: 'Not in table'. 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
✓
The 'summary-only' keyword suppresses more specific routes, so 10.0.3.0/24 is not advertised.
The 'summary-only' keyword in aggregate-address suppresses all more specific routes, including 10.0.3.0/24, from being advertised. This causes the specific prefix to be missing from the BGP table, leading to unreachability if the summary route does not have a valid next-hop or if the specific route is needed for traffic engineering.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 more specific routes, so 10.0.3.0/24 is not advertised.
Why this is correct
With summary-only, only the aggregate is advertised; specifics are suppressed, causing loss of reachability to 10.0.3.0/24.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VRF CUSTOMER does not have the route 10.0.3.0/24 in its routing table.
Why it's wrong here
The route is expected to be present.
✗
The aggregate-address command is missing the 'as-set' keyword, causing routing loops.
Why it's wrong here
Missing as-set affects AS path, not route suppression.
✗
The network statement for 10.0.0.0/22 is missing; need to advertise the aggregate.
Why it's wrong here
Aggregate-address does not require network statement.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
MPLS Operations — This question tests MPLS Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'summary-only' keyword suppresses more specific routes, so 10.0.3.0/24 is not advertised. — The 'summary-only' keyword in aggregate-address suppresses all more specific routes, including 10.0.3.0/24, from being advertised. This causes the specific prefix to be missing from the BGP table, leading to unreachability if the summary route does not have a valid next-hop or if the specific route is needed for traffic engineering.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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