JN0-106 Operational Monitoring and Maintenance Practice Test 5 — 15 Questions

Question 1

Which TWO methods can be used to restore a previous configuration on a Juniper device? (Select two.)

Accepted Answer

load override /config/rescue.conf. The 'load override /config/rescue.conf' command replaces the entire candidate configuration with the contents of the rescue configuration file, effectively restoring a previously saved baseline configuration. The rescue configuration is a special, manually saved configuration that persists across reboots and can be used to recover from configuration errors.

Answer

commit confirmed

Answer

load replace previous

Answer

rollback 0

Question 2

You are a network administrator for a large enterprise. The Juniper EX4300 switch that serves as the distribution layer for the finance department is experiencing high CPU utilization. Users are complaining of slow network performance. You have accessed the switch via console and notice that the CPU load is consistently above 90%. You need to identify the process causing the high CPU usage. Which command should you use?

Accepted Answer

'show system processes' to list all processes and their CPU usage.. The 'show system processes' command displays a list of all running processes along with their CPU and memory usage, allowing you to identify which process is consuming excessive CPU resources. This is the direct method to pinpoint the offending process on a Juniper EX4300 switch running Junos OS.

Answer

'show task summary' to see kernel task CPU usage.

Answer

'show system resources' to check memory and CPU.

Answer

'show system statistics' to view overall system stats.

Question 3

A Juniper SRX300 firewall is deployed at a branch office. The firewall's disk space on /var is critically low, causing logs to stop writing and system performance degradation. You need to free up space quickly without deleting logs (they are required for compliance). Which action should you take?

Accepted Answer

Compress old log files using 'request system storage compress'.. The 'request system storage compress' command compresses inactive log files on the /var partition, freeing up disk space without deleting any logs. This preserves the logs for compliance requirements while immediately alleviating the low disk space condition. The command targets files that are not currently being written to, such as rotated or archived logs, and compresses them using gzip.

Answer

Increase the /var partition size using LVM.

Answer

Enable log rotation with smaller retention to prevent future growth.

Answer

Move logs to an NFS mount using 'file copy' and delete local copies.

Question 4

A service provider has two MX routers (R1 and R2) connected via two separate physical links. Both links are in an aggregated Ethernet bundle (ae0). The ae0 interface is configured with LACP active on both sides. Recently, a fiber cut occurred on one of the member links, and the aggregated interface continued working. However, after the fiber was repaired, the network operator noticed that the restored link is not being re-added to the bundle. 'show lacp interfaces' indicates the link is in a 'detached' state. The operator checks 'show interfaces diagnostics optics' and finds that the optical parameters are normal. Which action should the operator take to restore the link to the bundle without affecting traffic?

Accepted Answer

Remove and re-add the member link from the ae0 configuration. The 'detached' state indicates LACP negotiation failed or is stuck, even though the physical link is up. The proper fix is to reinitialize LACP on that member link. In Junos, 'clear lacp interfaces' accomplishes this, but that command is not offered as an option. Option B, removing and re-adding the member link from the ae0 configuration, forces the interface to be re-created and LACP to restart. Because the link is already detached and not forwarding traffic, this action does not affect active traffic on the bundle.

Answer

Reboot the router to clear all LACP states

Answer

Issue the 'clear lacp statistics' command on the interface to reset LACP negotiation on that link

Answer

Replace the SFP module on the restored link

Question 5

An engineer needs to check for packet errors on an interface. Which two commands provide error counter information? (Choose two.)

Accepted Answer

show interfaces extensive. The correct commands are 'show interfaces extensive' (Option C) and 'show interfaces errors' (Option D). 'show interfaces extensive' provides detailed interface statistics, including error counters like CRC errors, frame errors, etc. 'show interfaces errors' displays a summary of error counts for all interfaces. Option A ('show interfaces diagnostics') is used for optical diagnostics, not packet errors. Option B ('show interface errors') uses incorrect syntax (singular 'interface'); the correct command uses the plural form. Option E ('show interfaces terse') shows a brief interface status without error details.

Answer

show interfaces diagnostics

Answer

show interface errors

Answer

show interfaces terse

Question 6

Refer to the exhibit. A network administrator notices intermittent connectivity issues. Based on the log messages, what is the most likely cause?

Accepted Answer

The interface ge-0/0/0 is experiencing a physical layer issue causing it to flap.. The log shows rapid down/up events (flapping) on interface ge-0/0/0. This pattern typically indicates a physical layer problem such as a faulty cable or transceiver. Option B is plausible but the traps are symptoms, not the cause. Option C is less likely because the adjacency recovers quickly. Option D is unsupported by the logs.

Answer

The ISIS protocol has a configuration error that prevents adjacency.

Answer

An SNMP trap is causing a loop in the network.

Answer

The router's MIB is corrupted causing false logs.

Question 7

A company runs Juniper MX routers in a data center. They have a monitoring server that polls SNMP every 5 minutes. Recently, the monitoring server reported that interface ge-0/0/1 on router R1 has been down for 3 hours, but the network operations center says that no alarms were triggered and the link appears up from their end. The administrator logs into R1 and runs 'show interfaces ge-0/0/1' and sees that the interface is up with no errors, but the output shows 'Last flapped: 3 hours ago', which matches the monitoring downtime. Further investigation reveals that the interface has been administratively disabled and re-enabled at that time by an automated script that was later rolled back. The monitoring server uses ifAdminStatus and ifOperStatus OIDs. Which action would most reliably prevent this false positive in the future?

Accepted Answer

Monitor ifLastChange OID along with ifOperStatus to detect administrative flapping.. To prevent false positives from administrative interface down events, the monitoring system should correlate ifAdminStatus with ifOperStatus and suppress alarms when ifAdminStatus is down. ifLastChange only reflects changes to ifOperStatus and cannot indicate whether a down event was caused by an administrative action. The provided explanation incorrectly claims ifLastChange can detect administrative flapping.

Answer

Use 'show interfaces extensive' to confirm interface status.

Answer

Change the SNMP polling interval to 1 minute.

Answer

Disable the automated script that caused the administrative disable.

Question 8

You are managing a Juniper MX router that serves as a BGP route reflector for multiple customer VPNs. The router has two routing engines (RE0 and RE1) in a graceful switchover (GRES) configuration. During a routine maintenance window, you need to upgrade the Junos OS from version 18.1R1 to 20.2R2. The upgrade must minimize traffic disruption. You have already staged the new image on both REs. Which sequence of commands ensures minimal impact?

Accepted Answer

On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot. It performs a non-disruptive upgrade by first upgrading the backup RE (RE1), then switching mastership to the upgraded RE, and finally upgrading the original master RE. This sequence leverages Graceful Routing Engine Switchover (GRES) to maintain BGP sessions and VPN forwarding during the upgrade, minimizing traffic disruption.

Answer

On RE0: request system software add jinstall-20.2R2.tgz reboot; then on RE1 same command

Answer

On RE0: request system reboot (without adding software)

Answer

On both REs: request system software add jinstall-20.2R2.tgz reboot

Question 9

You are managing a Juniper MX240 router at a small ISP. The router has been operating normally for months. This morning, a customer reports intermittent packet loss on their connection, which is served by interface ge-0/0/2. You SSH into the router and run 'show interfaces ge-0/0/2 extensive'. The output shows input errors increasing rapidly, including CRC errors and frame errors. The interface is up/up. You also notice that the interface statistics show a high number of carrier transitions. The cable connecting the router to the customer's CPE was recently replaced by the customer's technician. What is the most likely cause of the errors and the correct action to resolve the issue?

Accepted Answer

Replace the cable with a known good one because CRC and frame errors indicate a physical layer problem such as a damaged cable or loose connector.. CRC and frame errors increasing rapidly, combined with a high number of carrier transitions, are classic symptoms of a physical-layer issue. Since the cable was recently replaced by the customer's technician, the most likely cause is a faulty cable or a loose connector. Replacing the cable with a known good one directly addresses the physical layer problem, which is the root cause of these errors.

Answer

Clear the MAC address table on the router to fix possible MAC flapping issues.

Answer

Administer a 'shutdown' and 'no shutdown' on the interface to reset the line protocol.

Answer

Change the interface speed and duplex settings to auto-negotiate because the errors are due to a mismatch between the router and CPE.

Question 10

Which two events typically trigger a change to the routing table? (Choose two.)

Accepted Answer

Interface state change. An interface state change (up/down) directly affects the reachability of directly connected networks. When an interface goes up, Junos adds the corresponding directly connected route to the routing table; when it goes down, the route is removed. Similarly, a BGP neighbor reset causes the BGP session to be torn down and re-established, which triggers the withdrawal and re-advertisement of all BGP routes, thereby modifying the routing table.

Answer

System uptime

Answer

Log file rotation

Answer

Configuration commit

Question 11

A network administrator wants to see the current CPU load average over the last 1, 5, and 15 minutes on a Juniper device. Which command displays this information?

Accepted Answer

show system uptime. The 'show system uptime' command displays the system's uptime along with the load averages for the last 1, 5, and 15 minutes. This is the standard Junos command for viewing CPU load averages, which are calculated based on the number of processes in the run queue over those time intervals.

Answer

show chassis routing-engine

Answer

show system processes

Answer

show system statistics

Question 12

A technician notices that the /var partition is filling up on a Juniper device. Which action would be most appropriate to free up space while preserving critical logs?

Accepted Answer

Run 'request system storage cleanup'. The 'request system storage cleanup' command is the correct action because it safely removes non-essential files such as old log files, core dumps, and temporary files that are no longer needed, while preserving critical logs and configuration files. This command performs a controlled cleanup without risking the deletion of important operational data, making it the most appropriate method for freeing up space on the /var partition.

Answer

Delete core files manually

Answer

Reboot the device

Answer

Delete all files in /var/log

Question 13

A network operator needs to upgrade the Junos OS on the backup RE (re1) of a dual-RE system. Which procedure ensures that only the backup RE is upgraded and rebooted without affecting the forwarding plane?

Accepted Answer

Use 'request system software add re1' and then 'request system reboot re1'. The 'request system software add re1' command installs the Junos OS image only on the backup Routing Engine (RE1), and the subsequent 'request system reboot re1' reboots only that RE. In a dual-RE system, this procedure isolates the upgrade to the backup RE, ensuring the forwarding plane remains active on the primary RE (RE0) and no traffic disruption occurs.

Answer

Use 'request system software add <image> both' and then 'request system reboot both'

Answer

Use 'request system software add <image> re0' and then 'request system reboot re0'

Answer

Copy the image to both REs and reboot the backup RE with 'request system reboot slice 1'

Question 14

Which command displays the status of all configured interfaces, including administrative and operational status?

Accepted Answer

show interfaces terse. The 'show interfaces terse' command displays a concise summary of all interfaces, including their administrative status (up or down) and operational status (up or down), along with protocol states. This makes it the correct choice for quickly viewing the status of all configured interfaces in a single output.

Answer

show configuration interfaces

Answer

show chassis hardware

Answer

show interface statistics

Question 15

A network engineer suspects a hardware issue on an interface. Which command provides the most detailed hardware error counters, including CRC errors, framing errors, and runts?

Accepted Answer

show interfaces extensive. The 'show interfaces extensive' command provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command displays per-interface statistics at the physical layer, such as input errors, output errors, and specific error types like frame, runts, giants, and CRC errors, which are essential for diagnosing hardware issues.

Answer

show interfaces diagnostics optics

Answer

show interfaces detail

Answer

show log messages