JN0-106 Operational Monitoring and Maintenance Practice Test 6 — 15 Questions

Question 1

An operator wants to monitor the temperature and voltage sensors on a Juniper chassis. Which command displays current sensor readings?

Accepted Answer

show chassis environment. The 'show chassis environment' command displays real-time sensor readings for temperature, voltage, and fan status on Juniper devices. It is the standard operational command for monitoring chassis environmental health, directly matching the operator's requirement to check temperature and voltage sensors.

Answer

show chassis hardware

Answer

show system health

Answer

show log messages | match temperature

Question 2

A technician needs to view the last 50 log messages from the system log file. Which command accomplishes this?

Accepted Answer

show log messages | last 50. The 'show log messages | last 50' command displays the last 50 lines from the /var/log/messages file on a Junos device. The pipe to 'last' is a Junos CLI filter that outputs only the final N lines of the command output, which is exactly what is needed to view the most recent log entries.

Answer

show system log messages

Answer

monitor start messages

Answer

show system syslog

Question 3

Which command is used to verify that the current active configuration is the same as the candidate configuration?

Accepted Answer

show | compare. The command `show | compare` displays the differences between the candidate configuration and the active (committed) configuration. If there are no differences, the candidate configuration is identical to the active configuration. This is the correct way to verify whether the candidate configuration matches the active configuration in Junos.

Answer

commit check

Answer

show configuration

Answer

show system configuration

Question 4

Which TWO commands can be used to monitor system log messages in real-time?

Accepted Answer

monitor start messages. The 'monitor start messages' command streams the contents of the /var/log/messages file in real-time, allowing you to monitor system log messages as they are generated. 'monitor start interactive-commands' (Option D) monitors logs specific to interactive CLI commands, not general system log messages, so it does not satisfy the stem. The other options ('show log messages | last 100', 'show system log messages', 'show configuration system syslog') either display historical data or configuration, not real-time system log monitoring.

Answer

show log messages | last 100

Answer

show system log messages

Answer

show configuration system syslog

Answer

monitor start interactive-commands

Question 5

Which TWO commands can be used to view the current routing table entries for IPv4 unicast routes?

Accepted Answer

show route table inet.0. `show route table inet.0` explicitly displays the IPv4 unicast routing table (inet.0) in Junos. Option D is correct because `show route` without any filter defaults to showing all routes in the inet.0 table, which is the primary IPv4 unicast routing table.

Answer

show route protocol static

Answer

show forwarding-table

Answer

show route table inet6.0

Question 6

Refer to the exhibit. An administrator notices the /var partition is nearly full. Which command can be used to safely reclaim disk space?

Accepted Answer

request system storage cleanup. The 'request system storage cleanup' command safely removes old log files, core dumps, and other temporary files that are no longer needed, freeing up space on the /var partition without risking system stability. This is the recommended Junos method for reclaiming disk space because it targets only files that can be safely deleted.

Answer

request system reboot

Answer

delete /var/log/messages

Answer

request system software delete

Question 7

Refer to the exhibit. Based on the log messages, what is the most likely cause of the interface flapping?

Accepted Answer

Faulty SFP module. The log messages show repeated link up/down events (interface flapping). In Junos, interface flapping is most commonly caused by a faulty SFP module, as physical layer issues like degraded optics or loose connections trigger continuous link transitions. The logs typically show 'link up' followed by 'link down' without any protocol-level errors, pointing to a hardware fault rather than configuration mismatches.

Answer

MTU mismatch

Answer

Duplicate IP address

Answer

Spanning tree topology change

Question 8

Refer to the exhibit. Which interface has a physical layer connectivity problem?

Accepted Answer

ge-0/0/1. Interface ge-0/0/1 shows 'Physical link is Down' in the output, which directly indicates a physical layer connectivity problem. The 'Device present' field is also 'No', confirming that no transceiver or cable is detected, which is a Layer 1 issue.

Answer

ge-0/0/2

Answer

ge-0/0/0

Answer

ge-0/0/3

Question 9

An engineer needs to check if the device has any pending changes that have not been committed. Which operational command should they run?

Accepted Answer

show configuration | compare. The 'show configuration | compare' command displays the differences between the candidate configuration (changes made but not yet committed) and the active configuration. This allows the engineer to see any pending changes that have not been committed, which is exactly what the question asks.

Answer

show system configuration

Answer

show system rollback

Answer

show system commit

Question 10

An administrator is asked to check the system log files for any error messages related to interface failures. Which command would be most efficient?

Accepted Answer

show log messages. 'show log messages' is the standard JUNOS command to display the contents of the /var/log/messages file. While it does not include a filter, it is the only valid command among the options that allows the administrator to view existing system log messages. The other options are either invalid commands (B and D) or used for real-time monitoring (A), which is not efficient for checking historical log files.

Answer

monitor start messages | match "error"

Answer

show log file messages | match "error"

Answer

show system syslog messages

Question 11

Which TWO commands can be used to view the system log messages on a Juniper device? (Select two.)

Accepted Answer

show log messages. 'show log messages' displays the contents of the default system log file, /var/log/messages, which contains kernel, daemon, and system-level messages. Option C is correct because 'monitor start messages' provides a real-time tail of the same /var/log/messages file, allowing live monitoring of system log entries as they are written.

Answer

show log dcd

Answer

show log file

Answer

show system messages

Question 12

Your company runs a Juniper MX480 router as the core gateway. The router has been experiencing intermittent connectivity issues with a remote site over a point-to-point OC3 link. Users report that the link goes down for a few seconds several times a day. You suspect that the issue might be related to physical layer errors or framing. You need to determine the cause and collect relevant data to present to the service provider. Which course of action should you take first?

Accepted Answer

Run 'monitor interface so-0/0/0' and observe for any CRC errors or alarms over a period of time.. 'monitor interface so-0/0/0' provides real-time, continuous display of interface counters and alarms, allowing you to observe CRC errors, framing errors, or alarms (e.g., LOS, LOF) as they occur. This is the most direct way to capture transient physical-layer issues on a SONET/SDH OC3 link without disrupting service, making it the appropriate first step before escalating to the service provider.

Answer

Perform a loopback test on the interface using 'test interface so-0/0/0'.

Answer

Review the system syslog file using 'show log messages' and search for interface down messages.

Answer

Immediately replace the serial interface card to rule out hardware failure.

Question 13

You are a junior network engineer tasked with upgrading the Junos OS on a pair of EX3400 switches that are in a Virtual Chassis. You have downloaded the new software image to the primary switch. Before performing the upgrade, you must verify the image's integrity and check the current version. Which sequence of commands should you use?

Accepted Answer

Run 'show version' and then 'request system software validate /var/tmp/junos-new.tgz'.. 'show version' displays the current Junos OS version running on the switch, which is necessary to confirm the starting point before an upgrade. Then 'request system software validate /var/tmp/junos-new.tgz' performs a checksum verification and package integrity check on the image file without installing it, ensuring the image is not corrupted. This sequence directly addresses the two tasks: verifying the image's integrity and checking the current version.

Answer

Run 'show system uptime' and then 'request system software add /var/tmp/junos-new.tgz'.

Answer

Run 'show system software' and then 'request system software add validate'.

Answer

Run 'show configuration system software' and then 'file checksum sha256 /var/tmp/junos-new.tgz'.

Question 14

Which two commands can be used to monitor real-time interface statistics and errors on a Junos device?

Accepted Answer

show interfaces extensive ge-0/0/0 | refresh 1. The 'show interfaces extensive ge-0/0/0 | refresh 1' command displays detailed interface statistics and errors, and the 'refresh 1' pipe modifier automatically updates the output every second, enabling real-time monitoring. Option D is correct because the 'monitor interface ge-0/0/0' command is specifically designed for real-time monitoring of interface counters and errors, refreshing the display at a default interval of 1 second. Both commands provide live views of interface statistics such as input/output packets, errors, drops, and CRC errors.

Answer

show interfaces terse

Answer

show interfaces ge-0/0/0

Answer

monitor security log

Question 15

A network administrator notices that the CPU utilization on an MX240 router has been consistently above 90% for the past hour. Users are reporting intermittent connectivity issues. The administrator logs in and runs 'show system processes extensive' which shows the Routing Protocol Daemon (rpd) consuming 70% of the CPU. Further investigation reveals that the router has over 5000 BGP prefixes from multiple peers. The administrator suspects that the high CPU is due to continuous route processing. What should the administrator do to immediately reduce CPU load while maintaining network stability?

Accepted Answer

Apply a prefix-limit on each BGP session to restrict the number of prefixes received. Applying a prefix-limit on each BGP session immediately restricts the number of prefixes the router will accept from peers. This prevents the Routing Protocol Daemon (rpd) from processing excessive BGP updates, reducing CPU load while maintaining network stability by keeping existing sessions and routes intact. The prefix-limit action (e.g., with a teardown threshold) ensures the router does not accept more prefixes than it can handle, directly addressing the root cause of high CPU usage.

Answer

Perform a 'show log messages' to check for errors before taking action

Answer

Bounce all BGP sessions by clearing them with 'clear bgp neighbor *'

Answer

Disable BGP multipath to reduce route processing