JN0-106 Junos OS Fundamentals Practice Question
Which THREE actions can be performed in operational mode on a Junos device?
⚠ Common exam trap
The trap here is that candidates familiar with Cisco IOS may mistakenly think that configuration commands like 'commit' or 'set interface' can be executed in operational mode, but Junos strictly enforces the separation between operational and configuration 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
✓
Ping a remote host
In Junos, operational mode is the CLI mode entered after login (prompt user@host>), used for monitoring and controlling device state. Option B (Ping a remote host) is correct because the ping command is an operational-mode command used to test reachability to a remote host. Option D (View system logs) is correct because operational mode provides commands such as show log messages to inspect system log files. Option E (Reboot the chassis) is correct because the request system reboot command is executed from operational mode to restart the device. Options A and C are not operational-mode actions: committing configuration changes (commit) and configuring interface IP addresses (set interfaces ...) are performed in configuration mode, which is entered with the configure command.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Commit configuration changes
Why it's wrong here
In Junos, the commit command is valid only from configuration mode, accessed via the 'configure' command at the CLI. It applies the candidate configuration to the active configuration after validation. Operational mode lacks commit because it is designed for monitoring and operational actions, not for altering configuration state.
- ✓
Ping a remote host
Why this is correct
Pinging a remote host is a standard operational-mode command in Junos, executed as 'ping <address>' from the CLI's operational prompt (user@router>). It sends ICMP echo requests and displays round-trip statistics without changing any system state. Because it performs a connectivity test rather than a configuration change, it is correctly classified as an operational action.
- ✗
Configure interface IP addresses
Why it's wrong here
Assigning IP addresses to interfaces requires entering configuration mode and editing the 'interfaces' hierarchy, for example with 'set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.1/24'. Operational mode only offers read-only visibility of interface settings, such as 'show interfaces terse' or 'show configuration interfaces'. The CLI deliberately separates these modes so that configuration changes are validated and committed atomically, preventing accidental live changes.
- ✓
View system logs
Why this is correct
The 'show log' command family in operational mode displays the contents of syslog files, such as 'show log messages' for the main system log. This is a read-only troubleshooting operation that allows operators to inspect events without modifying configuration. Queries like 'show log interactive-commands' are commonly used for security auditing and are available at the operational prompt.
- ✓
Reboot the chassis
Why this is correct
Issuing 'request system reboot' from the operational mode triggers a controlled restart of the Junos device, allowing for maintenance or applying some kernel-level changes. This is an operational-mode command because it is a runtime action, not a configuration edit; it does not alter the candidate or active configuration. It may require superuser privileges, but the command is still executed from the operational prompt.
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