JN0-106 User Interfaces Practice Question
A junior engineer accidentally enters 'set interfaces ge-0/0/0 unit 0 family inet address 192.0.2.1/24' in operational mode. What will happen?
⚠ Common exam trap
The trap here is that candidates accustomed to Cisco IOS, where 'configure terminal' is not required for every command and some configuration commands can be entered from privileged EXEC mode, mistakenly assume Junos behaves similarly, leading them to expect the command to succeed or the CLI to auto-switch modes.
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
✓
An error message is displayed, and no changes are made.
In Junos OS, the 'set' command is a configuration mode command used to modify the candidate configuration. When entered in operational mode (indicated by the '>' prompt), the CLI does not recognize it as a valid operational command. Junos will immediately display an error message such as 'unknown command' and make no changes to the running or candidate configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
An error message is displayed, and no changes are made.
Why this is correct
When a `set` command is entered at the operational-mode prompt (`user@host>`), the Junos CLI parser immediately recognizes that `set` is not a valid operational command. It displays an error such as `error: unknown command` or `syntax error`, and because the command is rejected at parse time, no changes are made to the running or candidate configuration. The CLI does not attempt to reinterpret the input or apply any partial configuration.
- ✗
The IP address is configured successfully.
Why it's wrong here
Operational mode in Junos only accepts operational commands like `show`, `ping`, `request`, and `monitor`; configuration commands like `set`, `edit`, and `delete` are not recognized there. Since the CLI checks the current mode's command hierarchy before execution, the parser cannot map `set interfaces ge 0 0` to an IP configuration action. Therefore, no IP address is ever configured, and the command simply fails with an error.
- ✗
The command is queued for later execution.
Why it's wrong here
Junos does not implement any command queuing or deferred execution mechanism for CLI inputs. Commands are processed synchronously: the parser either accepts them and executes them immediately, or rejects them with an error. There is no background queue or delayed processing feature in the CLI, so the idea that the command is queued for later execution is fundamentally unsupported by the architecture.
- ✗
The CLI automatically switches to configuration mode.
Why it's wrong here
The Junos CLI does not automatically switch between operational and configuration modes based on the command entered. Entering configuration mode requires an explicit user action, such as typing `configure` or `edit`, and the prompt changes from `>` to `#`. When a user types `set` in operational mode, the CLI does not infer that they intended to enter configuration mode; it simply reports an error because the command is invalid in the current mode.
About these practice questions
Courseiva writes every JN0-106 question from scratch — 326 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
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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.