JNCIA-JUNOS Operational Monitoring and Maintenance Practice Test 6 — 15 Questions

Question 1

An administrator suspects that an interface is flapping but the router is remote and the connection is intermittent. The administrator wants to monitor the interface status without maintaining an SSH session. Which approach should be used?

Accepted Answer

Configure event-options to trigger on interface down and send syslog. Option A is correct because Junos event-options allows you to define an event policy that triggers on a specific event, such as an interface down transition, and then executes an action like sending a syslog message. This enables asynchronous monitoring without requiring an active SSH session, making it ideal for intermittent connectivity scenarios.

Answer

Use 'monitor interface ge-0/0/0' and rely on terminal persistence

Answer

Use 'monitor start' to capture logs

Answer

Schedule a cron job to run 'show interfaces ge-0/0/0' every minute and log output

Question 2

A Juniper device is running out of disk space on the /var partition. Which command can be used to check disk usage?

Accepted Answer

show system storage. The correct command to check disk usage on a Juniper device is 'show system storage'. This command displays detailed information about disk partitions, including total, used, and available space, as well as the percentage of usage for each mounted filesystem, such as /var. It is the standard operational mode command for monitoring storage utilization in Junos OS.

Answer

show system disk-space

Answer

show system memory

Answer

show system resource

Question 3

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

Accepted Answer

show log messages. Option B is correct because '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 4

Which THREE operational commands are used to monitor interface statistics and status? (Select three.)

Accepted Answer

show interfaces terse. Option A is correct because 'show interfaces terse' provides a concise summary of all interfaces, including their administrative and operational status (up/down) and protocol states, making it ideal for a quick health check. Option B is correct because 'monitor interface' is a real-time operational command that continuously displays interface statistics and status updates, useful for live traffic observation. Option C is correct because 'show interfaces' displays detailed interface statistics, including packet counts, errors, and operational status, which is the primary command for in-depth interface monitoring.

Answer

show log interfaces

Answer

show interfaces diagnostics

Question 5

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

Accepted Answer

load override /config/rescue.conf. Option A is correct because 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 6

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.. Option A is correct because '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 7

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 8

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'.. Option D is correct because 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 9

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'.. Option C is correct because '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 10

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. Option C is correct because 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 11

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

Question 12

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

Issue the 'clear lacp statistics' command on the interface to reset LACP negotiation on that link. Option C is correct because the 'detached' state in LACP indicates that the link is physically up but LACP negotiation has failed or is stuck. The 'clear lacp statistics' command resets the LACP state machine on the specified interface, forcing it to re-initiate LACP PDUs and renegotiate with the peer. This restores the link to the bundle without disrupting active traffic on other member links.

Answer

Reboot the router to clear all LACP states

Answer

Remove and re-add the member link from the ae0 configuration

Answer

Replace the SFP module on the restored link

Question 13

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. Option B, 'show interfaces errors', provides a concise view of error counters per interface. Option C, 'show interfaces extensive', includes detailed error statistics. Option A shows a brief summary without errors. Option D is invalid syntax (singular 'interface'). Option E shows optical diagnostics, not packet errors.

Answer

show interfaces diagnostics

Answer

show interface errors

Answer

show interfaces terse

Question 14

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 15

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.. Option D is correct because ifLastChange provides the timestamp of the last state change. By cross-referencing ifLastChange with ifOperStatus, the monitoring system can detect that the 'down' event was administrative (ifAdminStatus changed) rather than a true link failure. Option A reduces polling interval but does not distinguish administrative changes. Option B disables the script, which is a temporary fix and not a monitoring improvement. Option C relies on manual verification, which is not automated.

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.