The correct answer is to configure 'area 2 area-range 10.0.0.0/16' on the ABR. This command performs OSPF area summarization on Junos by instructing the Area Border Router to advertise a single aggregate route into the backbone instead of all individual subnets from area 2, directly reducing the routing table size in area 0 while maintaining reachability. On the JNCIA-Junos exam, this concept tests your understanding of OSPF route summarization and the ABR’s role in controlling inter-area advertisements—a common trap is confusing this with the 'aggregate' route statement used for BGP or static routes, which does not apply to OSPF areas. Remember that 'area-range' is always configured on the ABR and only summarizes routes *into* the backbone, not within the same area. A useful memory tip: think of the ABR as the "gatekeeper" that uses area-range to shrink the map it hands to area 0.
JNCIA-JUNOS Routing Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. 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.
An enterprise uses OSPF across multiple areas. To reduce routing table size in the backbone area, the engineer wants to advertise a single summary route for all subnets in area 2. Which configuration is appropriate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure 'area 2 area-range 10.0.0.0/16' on the ABR
Option D is correct because the 'area-range' command on an Area Border Router (ABR) allows you to summarize a set of routes from a specific area into the backbone (area 0) by advertising a single aggregate route (e.g., 10.0.0.0/16) instead of all individual subnets. This reduces the routing table size in area 0 while still providing reachability to all subnets in area 2.
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.
✗
Configure a virtual-link between area 2 and area 0
Why it's wrong here
Virtual-links are for connecting non-backbone areas to area 0, not for summarization.
✗
Configure a default route from area 2 using 'default-metric'
Use a static route for the summary and redistribute it into OSPF
Why it's wrong here
Redistribution is not necessary; OSPF has native summarization.
✓
Configure 'area 2 area-range 10.0.0.0/16' on the ABR
Why this is correct
This summarizes area 2's routes into a single prefix for other areas.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'area-range' (which summarizes routes between areas) with 'virtual-link' (which fixes connectivity issues) or assume redistribution is needed for summarization, when OSPF's built-in ABR summarization is the correct and simplest method.
Detailed technical explanation
How to think about this question
The 'area-range' configuration on an ABR triggers OSPF to generate a type 3 summary LSA for the specified prefix, suppressing more specific type 3 LSAs for subnets within that range. This is defined in RFC 2328, Section 3.2, and is a fundamental OSPF feature for hierarchical design; in real-world deployments, it prevents backbone routers from carrying thousands of /24 routes from a large area, improving convergence and memory usage.
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.
TExam Day Tips
→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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Routing Fundamentals — This question tests Routing Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure 'area 2 area-range 10.0.0.0/16' on the ABR — Option D is correct because the 'area-range' command on an Area Border Router (ABR) allows you to summarize a set of routes from a specific area into the backbone (area 0) by advertising a single aggregate route (e.g., 10.0.0.0/16) instead of all individual subnets. This reduces the routing table size in area 0 while still providing reachability to all subnets in area 2.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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