- A
The security policy from the trust zone to the untrust zone is blocking traffic; you should create a policy allowing all traffic from the SRX itself.
Why wrong: Security policies control traffic through the device, not traffic originating from the device itself. Host-inbound traffic is controlled by zone settings, not policies.
- B
The interface ge-0/0/0 has an incorrect MAC address; you should clear the ARP cache.
Why wrong: ARP issues would affect all traffic, but internal users can access the internet, so ARP is working.
- C
The interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone; you should add the appropriate system services under the zone.
This is the most likely cause because the device cannot initiate traffic without explicit host-inbound traffic settings.
- D
The default route is missing or incorrect; you should add a default route via the internet gateway IP.
Why wrong: The stem states the routing table shows a default route, so this is not the issue.
Quick Answer
The answer is that the interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone, and you must add the appropriate system services to that zone. This is because, on a Juniper SRX, each security zone has a default setting that blocks all traffic destined to the device itself, including pings originated by the SRX. Even with a correct default route and security policies, the SRX drops its own outbound ICMP echo requests at the zone level before they leave the interface, or it drops the returning replies as inbound traffic to the device. On the JNCIA-Junos exam, this concept tests your understanding of the separation between transit traffic (handled by security policies) and host-inbound traffic (controlled by the `host-inbound-traffic` stanza under `security zones`). A common trap is assuming that a working default route and permissive policies are sufficient for device management traffic. Remember the mnemonic: "Ping the zone, not just the route"—you must explicitly permit system services like ping under the zone configuration for the SRX to talk to the outside world.
JNCIA-JUNOS User Interfaces Practice Question
This JNCIA-JUNOS practice question tests your understanding of user interfaces. 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.
You are a network engineer for a company that has just deployed a Juniper SRX firewall in a branch office. The device has multiple interfaces: ge-0/0/0 connected to the internet, ge-0/0/1 connected to the internal LAN (192.168.1.0/24), and ge-0/0/2 connected to a DMZ (10.0.0.0/24). After initial configuration, you attempt to ping from the SRX to a server on the internet (8.8.8.8) but receive no response. You also notice that internal users can access the internet. You have verified the routing table shows a default route via ge-0/0/0. The security policies appear correct. You suspect the issue is related to interface configuration. What is the most likely cause and the correct course of action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone; you should add the appropriate system services under the zone.
The SRX can ping internal hosts but not the internet because the interface ge-0/0/0 is in the untrust zone, which by default blocks all inbound traffic, including pings originated from the device itself. The 'host-inbound-traffic' configuration under the security zone allows system services such as ping, SSH, and SNMP to be received on that interface. Without it, even though the routing table and security policies are correct, the SRX will drop its own outbound ICMP echo requests before they can be sent, or drop the replies if they are treated as inbound traffic.
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 security policy from the trust zone to the untrust zone is blocking traffic; you should create a policy allowing all traffic from the SRX itself.
Why it's wrong here
Security policies control traffic through the device, not traffic originating from the device itself. Host-inbound traffic is controlled by zone settings, not policies.
- ✗
The interface ge-0/0/0 has an incorrect MAC address; you should clear the ARP cache.
Why it's wrong here
ARP issues would affect all traffic, but internal users can access the internet, so ARP is working.
- ✓
The interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone; you should add the appropriate system services under the zone.
Why this is correct
This is the most likely cause because the device cannot initiate traffic without explicit host-inbound traffic settings.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The default route is missing or incorrect; you should add a default route via the internet gateway IP.
Why it's wrong here
The stem states the routing table shows a default route, so this is not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse transit security policies (which control traffic passing through the device) with host-inbound traffic controls (which manage traffic destined to the device itself), leading them to incorrectly modify security policies instead of enabling system services under the zone.
Trap categories for this question
Command / output trap
The stem states the routing table shows a default route, so this is not the issue.
Detailed technical explanation
How to think about this question
On Junos, the 'host-inbound-traffic' configuration under a security zone explicitly lists which system services (ping, ssh, snmp, etc.) and protocols are allowed to terminate on the device itself. This is separate from transit security policies. A common oversight is that even if the SRX has a valid default route and correct security policies for transit traffic, the device's own management traffic (like ping to 8.8.8.8) is blocked unless the appropriate services are enabled under the zone for the egress interface. The 'show security zones' command can verify these settings.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone; you should add the appropriate system services under the zone. — The SRX can ping internal hosts but not the internet because the interface ge-0/0/0 is in the untrust zone, which by default blocks all inbound traffic, including pings originated from the device itself. The 'host-inbound-traffic' configuration under the security zone allows system services such as ping, SSH, and SNMP to be received on that interface. Without it, even though the routing table and security policies are correct, the SRX will drop its own outbound ICMP echo requests before they can be sent, or drop the replies if they are treated as inbound traffic.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This JNCIA-JUNOS 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-JUNOS exam.
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