The answer is that the route is rejected because it matches the prefix list. In Junos, a route policy evaluates routes sequentially through its terms; when a route matches a term’s "from" condition—here, the prefix list covering 172.16.0.0/12—the associated action (reject) is applied, and unless a later term explicitly accepts the route, the final action defaults to that reject. This tests your understanding of how prefix lists and policy evaluation interact on the JNCIA-Junos exam, where a common trap is assuming a missing "then accept" at the end of a policy means the route is implicitly accepted—it is not; without an explicit accept, the last matching term’s action stands. Memory tip: think of Junos policy as a firewall—once a match triggers a reject, the route is dropped unless a later term says "accept" to override it.
JNCIA-JUNOS Junos Configuration Basics Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos configuration basics. 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.
Exhibit
Refer to the exhibit.
```
user@router> show configuration | display set | match "policy-options"
set policy-options prefix-list BLOCK-RFC1918 10.0.0.0/8
set policy-options prefix-list BLOCK-RFC1918 172.16.0.0/12
set policy-options prefix-list BLOCK-RFC1918 192.168.0.0/16
set policy-options policy-statement DENY-RFC1918 term 1 from prefix-list BLOCK-RFC1918
set policy-options policy-statement DENY-RFC1918 term 1 then reject
set policy-options policy-statement DENY-RFC1918 term 2 then accept
```
Refer to the exhibit. A route policy named DENY-RFC1918 is configured. What is the final action of this policy for a route matching 172.20.0.0/16?
Refer to the exhibit.
```
user@router> show configuration | display set | match "policy-options"
set policy-options prefix-list BLOCK-RFC1918 10.0.0.0/8
set policy-options prefix-list BLOCK-RFC1918 172.16.0.0/12
set policy-options prefix-list BLOCK-RFC1918 192.168.0.0/16
set policy-options policy-statement DENY-RFC1918 term 1 from prefix-list BLOCK-RFC1918
set policy-options policy-statement DENY-RFC1918 term 1 then reject
set policy-options policy-statement DENY-RFC1918 term 2 then accept
```
A
The route is rejected because it matches the prefix list.
Correct; it matches the prefix list and term 1 rejects.
B
The route is accepted because it does not match the prefix list.
Why wrong: 172.20.0.0/16 matches 172.16.0.0/12.
C
The route is accepted because term 2 accepts all routes.
Why wrong: Term 2 is only reached if term 1 does not match, but here it matches.
D
The route is rejected only if the prefix is exactly 172.16.0.0/12.
Why wrong: Prefix lists match based on the prefix and length; partial matches are allowed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route is rejected because it matches the prefix list.
The route policy DENY-RFC1918 uses a prefix list that matches RFC 1918 private addresses, including 172.20.0.0/16 (which falls within the 172.16.0.0/12 range). Since the route matches the prefix list, term 1 applies a 'reject' action, and because no subsequent term explicitly accepts the route, the final action is reject.
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 is rejected because it matches the prefix list.
Why this is correct
Correct; it matches the prefix list and term 1 rejects.
Related concept
Read the scenario before looking for a memorised answer.
✗
The route is accepted because it does not match the prefix list.
Why it's wrong here
172.20.0.0/16 matches 172.16.0.0/12.
✗
The route is accepted because term 2 accepts all routes.
Why it's wrong here
Term 2 is only reached if term 1 does not match, but here it matches.
✗
The route is rejected only if the prefix is exactly 172.16.0.0/12.
Why it's wrong here
Prefix lists match based on the prefix and length; partial matches are allowed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a prefix list requires an exact prefix-length match, but in Junos, a route with a longer prefix length (e.g., /16) within the listed prefix (e.g., /12) is considered a match, causing the route to be rejected.
Detailed technical explanation
How to think about this question
In Junos, prefix lists evaluate routes based on the specified prefix and prefix-length range; a route with a longer prefix length (e.g., /16) that falls within the listed prefix (e.g., 172.16.0.0/12) is considered a match. The policy framework processes terms in order, and the first matching term's action (reject) is applied; if no term matches, the default action is to accept the route. This behavior is critical when filtering BGP routes to prevent private address leakage into the global routing table.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 is rejected because it matches the prefix list. — The route policy DENY-RFC1918 uses a prefix list that matches RFC 1918 private addresses, including 172.20.0.0/16 (which falls within the 172.16.0.0/12 range). Since the route matches the prefix list, term 1 applies a 'reject' action, and because no subsequent term explicitly accepts the route, the final action is reject.
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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