JN0-106 Operational Monitoring and Maintenance Practice Test 4 — 15 Questions

Question 1

You are troubleshooting an OSPF issue on a Juniper router. The router has a single interface ge-0/0/1 with IP 10.1.1.1/30 connected to a neighbor with IP 10.1.1.2/30. OSPF is configured area 0. The 'show ospf neighbor' command shows no neighbors. 'show interfaces ge-0/0/1 terse' shows the interface is up. 'show configuration protocols ospf' shows:
   area 0.0.0.0 {
       interface ge-0/0/1.0 {
           passive;
       }
   }
What is the problem?

Accepted Answer

The OSPF interface is configured as passive. The 'passive' statement under the OSPF interface configuration prevents the router from sending or processing OSPF Hello packets on that interface. Without Hello packets, the router cannot discover neighbors or form adjacencies, which is why 'show ospf neighbor' returns no neighbors even though the interface is operationally up.

Answer

The hello timer is too slow

Answer

Authentication is missing

Answer

The interface is administratively down

Question 2

A network engineer notices that traffic to a critical server is being dropped intermittently. The server is reachable via a static route on the Juniper router. The engineer checks the routing table and sees the route is present. Which operational command should the engineer use next to isolate the issue?

Accepted Answer

show route forwarding-table destination 10.0.0.1. The `show route forwarding-table destination 10.0.0.1` command displays the actual forwarding entry in the kernel's forwarding table (FIB). Even if the route is present in the routing table (RIB), a mismatch between the RIB and FIB can cause traffic drops. This command directly verifies whether the route has been installed into the forwarding table, isolating the issue to a possible hardware or kernel programming failure.

Answer

show interfaces terse

Answer

show route 10.0.0.1

Answer

show arp

Question 3

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 4

An administrator notices that the routing table is not updating as expected. Which command should be used to verify the routing table contents?

Accepted Answer

show route. The 'show route' command displays the routing table, which contains all active routes learned via static configuration, direct interfaces, or dynamic routing protocols such as OSPF, IS-IS, BGP, and RIP. If the routing table is not updating as expected, this command allows the administrator to verify the current routes, their next hops, and protocol sources to identify missing or incorrect entries.

Answer

show log

Answer

show system storage

Answer

show interfaces

Question 5

To monitor interface traffic in real-time, which operational command is most appropriate?

Accepted Answer

monitor interface. 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.

Answer

show interface traffic

Answer

request system reboot

Answer

show log

Question 6

A network engineer needs to check the system's disk space usage. Which command should be used?

Accepted Answer

show system storage. The 'show system storage' command displays disk space usage on Junos devices, including total, used, and available space for each mounted filesystem. This is the correct command for monitoring storage utilization, as it directly reports on the /, /config, and /var partitions critical for system operation.

Answer

show configuration

Answer

show version

Answer

show system uptime

Question 7

After a software upgrade, a router fails to boot with the new image. The engineer suspects the image is corrupted. What is the recommended method to recover?

Accepted Answer

Insert the rescue media and boot from it, then reinstall the image. When a Junos OS image is corrupted and the router fails to boot, the recommended recovery method is to boot from rescue media (such as a USB flash drive or a pre-configured rescue partition) and then reinstall the correct image. This bypasses the corrupted software on the internal storage and provides a clean environment for recovery, ensuring the router can be restored to a functional state.

Answer

Delete the current configuration and reboot

Answer

Reboot the router multiple times

Answer

Use the request system software add command with the force option

Question 8

An administrator wants to verify that BGP neighbors are established. Which command provides a summary of all BGP peer sessions?

Accepted Answer

show bgp summary. The 'show bgp summary' command is correct because it provides a concise, one-line-per-peer overview of all BGP sessions, including the peer IP address, AS number, state (e.g., Established), and counters for prefixes received. This is the standard command in Junos for quickly verifying that all BGP neighbors are in the Established state without the detailed per-neighbor output.

Answer

show bgp neighbor

Answer

show interfaces terse

Answer

show route protocol bgp

Question 9

A technician is troubleshooting a connectivity issue and needs to see the path packets take to a remote host. Which Junos command is appropriate?

Accepted Answer

traceroute. The `traceroute` command in Junos is the correct tool for tracing the path packets take to a remote host. It sends UDP probes with increasing TTL values and listens for ICMP Time Exceeded messages from intermediate routers, revealing each hop along the route. This directly matches the technician's need to see the path packets take.

Answer

monitor interface

Answer

ping

Answer

show route

Question 10

An administrator observes that the router's CPU utilization is consistently high. Which command helps identify which process is consuming the most CPU?

Accepted Answer

show system processes extensive. 'show system processes extensive', is correct because it displays detailed CPU utilization statistics for each running process on a Junos device, including the percentage of CPU time consumed. This allows the administrator to identify which specific process (e.g., routing protocol daemon, SNMP, or management process) is causing the high CPU load, enabling targeted troubleshooting.

Answer

show log messages

Answer

show system resource

Answer

show chassis routing-engine

Question 11

A network engineer needs to verify the checksum of a downloaded Junos image before installation. Which command is used?

Accepted Answer

file checksum sha256 . The `file checksum sha256 ` command computes the SHA-256 hash of the specified file, allowing the engineer to compare it against the published checksum from Juniper Networks to verify integrity and authenticity before installation. This ensures the image has not been corrupted or tampered with during download.

Answer

compare <filename> original

Answer

request system software validate <filename>

Answer

show system software

Question 12

Which two commands can be used to display real-time interface information? (Choose two.)

Accepted Answer

monitor interface. 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.

Answer

show log

Answer

request system reboot

Answer

show system storage

Question 13

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 14

Which three steps are part of a typical software upgrade process on a Juniper device? (Choose three.)

Accepted Answer

Issue the request system software add command. Option A is correct because the request system software add command is the standard Junos CLI command used to install a new software image onto the device, validating and unpacking it into the alternate partition. Option B is correct because the software image must first be downloaded to the device, and /var/tmp is the conventional directory used for staging the Junos package before installation. Option E is correct because after the new image is added, the device must be rebooted so it boots from the newly installed software on the alternate partition. Option C is not part of the process because interfaces do not need to be manually shut down; the reboot handles the transition. Option D is not required because Junos installs the new image to the alternate partition and the old image can remain, so deleting it beforehand is unnecessary and not a standard step.

Answer

Shut down all interfaces

Answer

Delete the old image before adding the new one

Question 15

Refer to the exhibit. An engineer notices that input drops are increasing. What is the most likely cause?

Accepted Answer

Buffer overflow. Input drops occur when the ingress interface's receive buffer is full and cannot accept more packets, typically due to the ingress rate exceeding the interface's ability to process or forward packets to the internal switch fabric. In Junos, this is often caused by microbursts or sustained oversubscription, not by a speed mismatch (which would show as errors or link flaps) or cable faults (which cause physical-layer errors). Buffer overflow is the correct answer because input drops directly indicate that the packet buffer has been exhausted.

Answer

Speed mismatch

Answer

Cable fault

Answer

CRC errors