Monitor Interface in Junos: Real-Time Statistics and Errors
Which two commands can be used to monitor real-time interface statistics and errors on a Junos device?
Quick Answer
The correct commands are monitor interface ge-0/0/0 and show interfaces extensive ge-0/0/0 | refresh 1, as both provide real-time interface statistics and errors on a Junos device. The monitor interface command is purpose-built for live tracking, automatically refreshing interface counters like input/output packets, drops, and CRC errors every second by default, while the show interfaces extensive command combined with the refresh 1 pipe modifier achieves the same effect by forcing a one-second update cycle. On the JNCIA-Junos exam, this topic tests your ability to distinguish between static show commands and dynamic monitoring tools, often appearing in questions about operational monitoring or troubleshooting link issues. A common trap is confusing the standard show interfaces command, which gives a single snapshot, with the real-time variants; remember that without refresh or the monitor keyword, you are not seeing live data. For a quick memory tip, think “monitor for motion, show for a photo” — the monitor command keeps the screen moving with fresh statistics, while show captures a static moment.
⚠ Common exam trap
A common mix-up: candidates confuse static 'show interfaces' commands (which provide a point-in-time snapshot) with real-time monitoring commands, leading them to select option B instead of the correct real-time options C and D.
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 extensive ge-0/0/0 | refresh 1
Option C, 'show interfaces extensive ge-0/0/0 | refresh 1', is correct because the 'extensive' keyword displays detailed statistics including error counters, and the '| refresh 1' pipe re-runs the command every second, giving real-time monitoring of a specific interface. Option D, 'monitor interface ge-0/0/0', is correct because the 'monitor interface' command is Junos's dedicated real-time interface statistics viewer, continuously updating counters such as packets, bytes, and errors for the named interface. Option A, 'show interfaces terse', only gives a one-time summary of interface status and addresses without error detail or refresh, so it is not real-time monitoring. Option B, 'show interfaces ge-0/0/0', provides a single snapshot of standard statistics and does not refresh or emphasize error counters. Option E, 'monitor security log', streams security log messages rather than interface statistics and errors, so it does not meet the requirement.
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
Why it's wrong here
'show interfaces terse' gives a one-line static summary per interface, not continuously refreshed real-time statistics or error counters. It is tempting because it does display interface state and counters, but real-time monitoring requires the 'monitor interface' command, which refreshes output at intervals.
- ✗
show interfaces ge-0/0/0
Why it's wrong here
'show interfaces ge-0/0/0' returns a single static snapshot of one interface's counters, not continuously refreshed real-time statistics. It is tempting because it does display error counters for that interface, but real-time monitoring requires 'monitor interface ge-0/0/0', which updates the display at set intervals.
- ✓
show interfaces extensive ge-0/0/0 | refresh 1
Why this is correct
The `| refresh 1` pipe re-runs the command every second, giving continuous real-time interface statistics and error counters for ge-0/0/0, which satisfies the monitoring requirement. The `extensive` keyword adds detailed error and counter data beyond the default summary output.
- ✓
monitor interface ge-0/0/0
Why this is correct
`monitor interface ge-0/0/0` streams live per-interface counters, refreshing every second, which satisfies the stem's real-time requirement. It displays input/output errors, drops and packet rates directly, unlike `show interfaces` snapshots or `show log messages`. Targeting a single interface keeps the output focused on the ge-0/0/0 statistics requested.
- ✗
monitor security log
Why it's wrong here
'monitor security log' streams security log entries, not interface statistics or error counters. It is tempting because 'monitor' commands do provide real-time streaming output, but this one targets security events; interface monitoring uses 'monitor interface', which refreshes counters continuously.
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Same concept, more angles
2 more ways this is tested on JN0-106
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. To monitor interface traffic in real-time, which operational command is most appropriate?
easy- A.show interface traffic
- B.request system reboot
- C.show log
- ✓ D.monitor interface
Why D: The 'monitor interface' command in Junos provides real-time, continuous display of interface statistics and traffic counters, updating every second by default. This is the correct operational command for live traffic monitoring, as it refreshes the output dynamically without requiring manual re-entry.
Variation 2. Which two commands can be used to display real-time interface information? (Choose two.)
easy- ✓ A.monitor interface
- ✓ B.monitor traffic
- C.show log
- D.request system reboot
- E.show system storage
Why A: Option A, `monitor interface`, is correct because it provides a real-time, continuously updating view of interface statistics such as traffic counters, errors, and link state on Juniper devices. Option B, `monitor traffic`, is correct because it captures and displays live packet-level traffic on an interface, showing real-time data as packets traverse the interface. Option C, `show log`, is incorrect because it displays stored log file contents rather than live interface information. Option D, `request system reboot`, is incorrect because it reboots the device and does not display interface data. Option E, `show system storage`, is incorrect because it reports disk and filesystem usage, not real-time interface information.
JA
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.