JN0-106 Junos OS Fundamentals Practice Question
A network administrator is configuring a new interface and wants to ensure that the interface is enabled and can pass traffic. Which configuration element is required?
⚠ Common exam trap
The trap here is that candidates familiar with Cisco IOS may expect an explicit 'no shutdown' command (or an 'enable' keyword) to bring an interface up, but Junos interfaces are enabled by default, and the critical missing piece is the IP address under the logical unit, not an administrative enable command.
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
✓
set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24
In Junos, an interface is administratively enabled by default (no explicit 'enable' command is needed), but to pass traffic it requires a logical unit with a configured protocol family and an IP address. The command 'set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24' creates unit 0, assigns the IPv4 address, and implicitly enables the interface for traffic forwarding. Without an address under a family, the interface cannot pass IP traffic even if it is administratively up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
set interfaces ge-0/0/0 enable
Why it's wrong here
There is no 'enable' statement in Junos interface configuration. Interfaces are administratively up by default; they only become down if you configure 'disable' or if the physical link is absent. The CLI will reject 'set interfaces ge-0/0/0 enable' because 'enable' is not a valid configuration node. To make the interface pass traffic, configure a logical unit and an address instead.
- ✓
set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24
Why this is correct
This command assigns an IPv4 address to unit 0 on ge-0/0/0, which automatically creates the logical interface and ties the inet address family to it. Once the address is committed, the interface is implicitly enabled and becomes operationally eligible to carry traffic. This is the correct minimal configuration for the task because it provides the required IP details and activates the interface without needing any additional 'enable' statement.
- ✗
set interfaces ge-0/0/0 unit 0 family inet
Why it's wrong here
This command creates unit 0 under the inet family but omits the essential 'address' statement. Without an IP address, the interface has no routable identity and the protocol family is effectively empty, so the interface cannot forward IPv4 traffic. Junos will accept this configuration at commit time, but it does not meet the goal of configuring a new interface for actual use. It is an incomplete step rather than an invalid one.
- ✗
set interfaces ge-0/0/0 disable
Why it's wrong here
This is a valid Junos configuration statement, but it performs exactly the opposite of the administrator's intention: it puts ge-0/0/0 into an administratively down state. When 'disable' is present, the interface is taken out of service even if the physical link is up, and no traffic will transit it. To enable the interface, you would need to remove this statement, not add it. Since the task is to configure a new interface, applying 'disable' is counterproductive.
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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.