Quick Answer
The answer is the `show interfaces terse irb.10` command. This command is the quickest way to verify the operational status of the IRB interface because it displays both the administrative and link state in a single line, showing whether the interface is physically and logically "up" or "down." Since the IRB interface must be operationally active for Layer 3 forwarding to the VLAN, a down state explains why users cannot reach the default gateway even though the IP is configured and VLAN-to-port associations are correct. On the JNCIA-Junos exam, this scenario tests your ability to isolate Layer 3 interface issues from Layer 2 VLAN problems—a common trap is wasting time checking VLAN membership or firewall filters when the IRB itself is disabled. A useful memory tip: "Terse tells the truth"—the `terse` modifier strips away verbose output, giving you the bare essentials of interface status and IP configuration in one glance.
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 managing a Juniper EX4300 switch that serves as a Layer 3 access switch for a campus network. The switch has multiple VLANs configured with IRB interfaces. Users in VLAN 10 report that they cannot reach the default gateway (IRB.10) even though other VLANs are working fine. You check the configuration and see that interface irb.10 is configured with an IP address. You also verify that the VLAN is associated with the correct access ports. However, when you ping the IRB.10 address from the switch itself, it fails. You suspect that the issue might be that the IRB interface is not 'up'. Which command would you use to quickly verify the operational status of the IRB interface?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
show interfaces terse irb.10
Shows operational status of the IRB interface.
show ethernet-switching table
Why wrong: Shows MAC address table.
show configuration interfaces irb.10
Why wrong: Shows configuration only.
show vlan
Why wrong: Shows VLAN information, not IRB status.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
show interfaces terse irb.10
Option A is correct because `show interfaces terse irb.10` displays the operational status (up/down) of the IRB interface along with its configured IP address. Since the issue is that the IRB interface may not be 'up', this command quickly confirms whether the interface is operationally active, which is essential for Layer 3 forwarding.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
show interfaces terse irb.10
Why this is correct
Shows operational status of the IRB interface.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
show ethernet-switching table
Why it's wrong here
Shows MAC address table.
show configuration interfaces irb.10
Why it's wrong here
Shows configuration only.
show vlan
Why it's wrong here
Shows VLAN information, not IRB status.
Common exam traps
The trap here is that candidates often check the configuration (`show configuration`) assuming it reflects the operational state, but Junos separates configuration from operational status, so a correctly configured IRB can still be down due to missing VLAN association or no active member ports.
Trap categories for this question
Command / output trap
Shows MAC address table.
Detailed technical explanation
IRB (Integrated Routing and Bridging) interfaces in Junos are logical Layer 3 interfaces that must be operationally 'up' to route traffic between VLANs. The `show interfaces terse` command provides a concise view of interface administrative and operational status (e.g., 'up' or 'down') along with protocol status, which is critical for troubleshooting Layer 3 connectivity. A common real-world scenario is when the underlying VLAN is not active on any physical port, causing the IRB to remain down even if configured correctly.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
The correct answer is: show interfaces terse irb.10 — Option A is correct because `show interfaces terse irb.10` displays the operational status (up/down) of the IRB interface along with its configured IP address. Since the issue is that the IRB interface may not be 'up', this command quickly confirms whether the interface is operationally active, which is essential for Layer 3 forwarding.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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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