JNCIA-SEC Network Address Translation Practice Question
An administrator configures Destination NAT so that traffic to public IP 198.51.100.10 is translated to internal server 10.1.1.10. However, when the administrator checks the security logs, they notice that the source IP addresses of incoming connections are being logged as the SRX internal interface IP instead of the actual external client IP addresses. What configuration error caused this?
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
✓
A Source NAT rule is inadvertently matching inbound traffic from the untrust zone and translating the client's source IP.
If source NAT is mistakenly applied to incoming destination NAT traffic (e.g., source NAT translates the external client IP to the SRX interface IP), the client IP is masked. This usually happens if a conflicting source NAT rule matches inbound traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Destination NAT inherently replaces the client source IP with the local interface IP by design.
Why it's wrong here
Destination NAT preserves the original source IP of the external client by default.
- ✗
The security policy action was set to 'log session-init' without specifying 'source-nat off'.
Why it's wrong here
'Source-nat off' is not a security policy action parameter.
- ✓
A Source NAT rule is inadvertently matching inbound traffic from the untrust zone and translating the client's source IP.
Why this is correct
Inbound Source NAT rules can overwrite or mask the original client source IP if misconfigured.
- ✗
Proxy ARP on the external interface causes source IP reflection.
Why it's wrong here
Proxy ARP answers ARP requests and does not alter packet source IP addresses.
Visual reference
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Juniper Networks exam blueprint
This JNCIA-SEC practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JNCIA-SEC exam.