JN0-106 User Interfaces Practice Question
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?
⚠ Common exam trap
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.
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
✓
show interfaces terse irb.10
`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.
Answer analysis
Option-by-option breakdown
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
The 'show interfaces terse irb.10' command provides a concise operational summary of the IRB interface, displaying its link state (up/down), protocol status, and the assigned IP address in a single line. This is the correct command because it directly verifies both the operational and protocol state of the IRB, which is essential for confirming that the L3 gateway is active. Unlike configuration commands, it reflects the current runtime status, including whether the underlying VLAN is active and associated with a physical port.
- ✗
show ethernet-switching table
Why it's wrong here
The 'show ethernet-switching table' command displays the Layer 2 MAC address forwarding table, showing learned MAC addresses, their VLANs, and output interfaces. While the IRB interface may have a MAC address and be present in this table, the command provides no information about the IRB's operational state, IP address, or whether it is up/down. This command is purely for switch forwarding decisions, not for validating the health of a routed interface, so it cannot answer questions about IRB status.
- ✗
show configuration interfaces irb.10
Why it's wrong here
The 'show configuration interfaces irb.10' command displays the configured settings for the IRB interface, such as its IP address, VLAN association, and any firewall filters, but it shows only the intended configuration, not the operational reality. A configuration can be valid yet the IRB remain operationally down due to missing parent VLAN activation, physical link issues, or protocol dependencies. Therefore, this command cannot verify whether the IRB is actually up and passing traffic; only operational commands like 'show interfaces terse' provide that real-time status.
- ✗
show vlan
Why it's wrong here
The 'show vlan' command provides a list of VLANs, their tags, and member interfaces, but it is limited to Layer 2 information and does not show the operational state or IP configuration of IRB interfaces. While it may confirm that a VLAN exists and is assigned to ports, it cannot tell you if the IRB associated with that VLAN is up, has an active IP address, or is functioning as a gateway. Since the question asks specifically about the IRB interface's operational status, this command is too high-level and Layer 2 oriented to be useful.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 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 JN0-106 exam.