The answer is that the route must match the prefix and prefix length exactly. This is correct because the 'exact' match type in a Junos prefix list enforces an identical match on both the network address and its subnet mask, meaning a route like 192.168.1.0/24 will only be accepted if it has that precise prefix and length, rejecting any more specific subnets (e.g., /25) or less specific supernets (e.g., /16). On the JNCIA-Junos exam, this concept tests your understanding of Junos routing policy framework, often appearing in troubleshooting scenarios where a route filter unexpectedly drops traffic due to a mismatch in prefix length. A common trap is confusing 'exact' with 'longer' or 'orlonger'—remember that 'exact' is the strictest match, requiring zero flexibility. For a memory tip, think of 'exact' as a lock and key: both the prefix and length must be cut identically to open the filter.
JNCIA-JUNOS Junos Configuration Basics Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos configuration basics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 administrator is troubleshooting a configuration issue where a route filter is unexpectedly dropping traffic. The filter uses an 'exact' match type. Which statement correctly describes the behavior of the 'exact' match type in a prefix list?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route must match the prefix and prefix length exactly.
Option B is correct because the 'exact' match type in a Junos prefix list requires the route's prefix and prefix length to match the specified prefix and length identically. This is defined in the Junos routing policy framework, where 'exact' is used for precise route filtering, such as matching a specific network like 192.168.1.0/24 without allowing any subnets or supernets.
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 route mask must be equal to or greater than the specified prefix length.
Why it's wrong here
This describes 'orlonger' match.
✓
The route must match the prefix and prefix length exactly.
Why this is correct
This is the definition of 'exact' match.
Related concept
Read the scenario before looking for a memorised answer.
✗
The prefix 0.0.0.0/0 is never matched by 'exact' filters.
Why it's wrong here
0.0.0.0/0 can be matched with 'exact' if specified.
✗
The route mask must be greater than the specified prefix length.
Why it's wrong here
This describes 'longer' match.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'exact' with 'orlonger' or 'longer' match types, especially when troubleshooting route filter behavior, leading them to select options that describe less restrictive matching.
Detailed technical explanation
How to think about this question
Under the hood, Junos prefix lists are evaluated in order, and the 'exact' match type performs a bitwise comparison of the prefix and a length check against the prefix-length value. In real-world scenarios, using 'exact' is critical for BGP route filtering to prevent unintended route leaks, such as when matching a specific customer prefix without allowing more specific prefixes that could cause suboptimal routing.
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 segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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.
Junos Configuration Basics — This question tests Junos Configuration Basics — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route must match the prefix and prefix length exactly. — Option B is correct because the 'exact' match type in a Junos prefix list requires the route's prefix and prefix length to match the specified prefix and length identically. This is defined in the Junos routing policy framework, where 'exact' is used for precise route filtering, such as matching a specific network like 192.168.1.0/24 without allowing any subnets or supernets.
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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