JNCIA-JUNOS Operational Monitoring and Maintenance — 20 Questions

Question 1

A network engineer notices that a device is not sending SNMP traps to the NMS. Which operational command should be used to verify SNMP configuration?

Accepted Answer

show snmp. The 'show snmp' command in Junos displays the current SNMP configuration, including community strings, trap destinations, and enabled trap groups. Since the issue is that the device is not sending SNMP traps, this command allows the engineer to verify that trap destinations are correctly configured and that the appropriate trap groups are enabled. Other commands like 'show system uptime' or 'show route' do not provide any SNMP-specific configuration details.

Answer

show system uptime

Answer

show route

Answer

show interfaces terse

Question 2

A network administrator is troubleshooting high CPU usage on a Juniper router. Which command helps identify which process is consuming the most CPU?

Accepted Answer

show system processes extensive. The 'show system processes extensive' command displays detailed information about all running processes, including CPU utilization, memory usage, and process IDs. This allows the administrator to identify which process (e.g., routing protocol daemon, management daemon) is consuming the most CPU cycles, directly addressing the troubleshooting need.

Answer

show log messages

Answer

show system memory

Answer

show interfaces

Question 3

After a software upgrade, BGP sessions are not establishing. The engineer runs 'show bgp summary' and sees that all sessions are in Idle state. What is the most likely cause?

Accepted Answer

The BGP group configuration is missing. The Idle state in BGP indicates that the session has not started the connection process, often because the BGP configuration is incomplete or missing. If the BGP group configuration is missing, the router has no peers to initiate sessions with, so all sessions remain in Idle. This is the most likely cause when all sessions are in Idle after a software upgrade, as configuration elements may be lost or not applied.

Answer

The interface is administratively down

Answer

The router has a full BGP table

Answer

The firewall filter is blocking ICMP

Question 4

A junior engineer needs to collect a snapshot of the current system state, including routing tables, interfaces, and configuration, for a support ticket. Which command achieves this?

Accepted Answer

request support information. The 'request support information' command is the correct choice because it collects a comprehensive snapshot of the current system state, including routing tables, interface details, configuration, logs, and other operational data into a single archive file. This is specifically designed for support tickets, as it bundles all relevant diagnostic information in one step, unlike individual show commands that only capture partial data.

Answer

show configuration

Answer

show interfaces

Answer

show route

Question 5

A network engineer wants to schedule a reboot of a Juniper device at 3:00 AM. Which command should be used?

Accepted Answer

request system reboot at 03:00. Option C is correct because the 'request system reboot at 03:00' command schedules a one-time reboot of the Juniper device at the specified time (3:00 AM). The 'at' parameter allows the engineer to set an absolute time for the reboot, which is the exact requirement for scheduling a reboot at a specific future time.

Answer

request system configuration rescue save

Answer

request system reboot

Answer

load override /config/juniper.conf.gz

Question 6

A router is experiencing intermittent packet loss. The engineer runs 'show interfaces ge-0/0/0 extensive' and notices a high number of input errors but no output errors. What is the most likely cause?

Accepted Answer

A faulty transceiver. A high number of input errors with no output errors on a Juniper interface typically indicates a Layer 1 issue at the receiving end. A faulty transceiver can cause signal degradation, leading to CRC errors, framing errors, or alignment errors, all of which are counted as input errors. Since output errors are absent, the problem is not with the router's transmission but with the incoming signal quality.

Answer

The cable is too long

Answer

MTU mismatch

Answer

The interface is oversubscribed

Question 7

An engineer needs to check the last time the configuration was changed. Which command provides this information?

Accepted Answer

show system commit. The 'show system commit' command displays the commit history, including the date, time, and user for each configuration change. This allows the engineer to see exactly when the last configuration was committed, which is the definitive way to determine the last time the configuration was changed.

Answer

show configuration | display set

Answer

show system alarms

Answer

show system uptime

Question 8

A BGP session is flapping. The engineer runs 'show log messages' and sees 'BGP recv Notification' with error code 'Cease'. What does this indicate?

Accepted Answer

The remote peer closed the connection. A BGP Cease notification indicates that the remote peer has closed the BGP session, often due to an administrative shutdown, configuration change, or error condition on the peer. The 'BGP recv Notification' message means the local router received this notification from the peer, so the remote peer initiated the closure.

Answer

The BGP table is full

Answer

The hold timer expired

Answer

The interface went down

Question 9

Which TWO statements are true about the 'show interfaces ge-0/0/0 extensive' command output?

Accepted Answer

It displays a detailed count of errors. The 'show interfaces ge-0/0/0 extensive' command in Junos OS provides a comprehensive view of the interface, including detailed error counters (e.g., CRC errors, frame errors, giants, runts) and traffic statistics (e.g., input/output bytes, packets, and rates). Option A is correct because the extensive output explicitly lists a detailed count of errors per interface, which is not available in the standard 'show interfaces' output. Option C is correct because traffic statistics such as unicast, multicast, and broadcast packets are included in the extensive output.

Answer

It includes only layer 1 information

Answer

It shows the interface configuration

Answer

It indicates the administrative status

Question 10

Which THREE commands are used for operational monitoring of routing protocols?

Accepted Answer

show isis adjacency. The 'show isis adjacency' command is used to verify the state of IS-IS neighbor adjacencies, which is a core operational monitoring task for the IS-IS routing protocol. It displays the interface, neighbor system ID, level, and adjacency state (e.g., Up, Down, Initializing), allowing an engineer to confirm that IS-IS neighbors are properly established.

Answer

show interfaces terse

Answer

show arp

Question 11

Which TWO statements are correct about the 'monitor interface' command?

Accepted Answer

It displays output in real-time. The 'monitor interface' command in Junos OS displays real-time statistics for the specified interface, updating continuously until the user terminates it. This is why option A is correct: it provides a live, dynamic view of interface counters like packets, errors, and bandwidth utilization.

Answer

It shows a static snapshot

Answer

It requires a 'start' parameter

Answer

It provides historical statistics

Question 12

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. Option C is correct because 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 13

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 14

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. Option D is correct because 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 15

Which THREE statements about the 'request system snapshot' command are true? (Choose three.)

Accepted Answer

It creates a recovery media for the device.. Option A is correct because the 'request system snapshot' command creates a bootable recovery media (e.g., USB or compact flash) that contains a copy of the current Junos OS and configuration. This allows the device to boot from that media in case of a system failure, effectively serving as a recovery tool.

Answer

It compresses the backup to save space.

Answer

It copies the active partition to the alternate partition on the same media.

Question 16

Based on the exhibit, which protocol is enabled on interface ge-0/0/0.0?

Accepted Answer

MPLS. The exhibit shows that interface ge-0/0/0.0 has the 'family mpls' statement configured under it, which enables MPLS on that interface. MPLS is explicitly enabled at the protocol family level, allowing the interface to participate in MPLS label switching.

Answer

IS-IS

Answer

BGP

Answer

OSPF

Question 17

You are the network administrator for a large enterprise with a Juniper MX480 router running Junos 18.2R3. The router has two Routing Engines (RE0 and RE1) in a graceful Routing Engine switchover (GRES) configuration. During a scheduled maintenance window, you need to upgrade the Junos OS to a newer version while minimizing traffic loss. The upgrade process requires a reboot of both REs. You have staged the software on both REs. Which sequence of commands should you use to perform the upgrade with minimal disruption?

Accepted Answer

On RE1 (backup): request system software add re1; request system reboot re1. After reboot, request chassis routing-engine master switch. On RE0 (now backup): request system software add re0; request system reboot re0.. Option D is correct because it performs a hitless upgrade by first upgrading and rebooting the backup RE (RE1), then performing a graceful mastership switch using 'request chassis routing-engine master switch', and finally upgrading and rebooting the former primary (now backup) RE0. This sequence ensures that during each RE reboot, the other RE remains active and continues forwarding traffic, leveraging GRES to maintain state and minimize packet loss.

Answer

On both REs: request system software add <image>; then request system reboot both REs simultaneously.

Answer

On RE0: request system software add re0; on RE1: request system software add re1; then request system reboot both.

Answer

On RE0 (primary): request system software add re0; request system reboot re0. After reboot, on RE1: request system software add re1; request system reboot re1.

Question 18

Which TWO statements correctly describe the use of the 'monitor traffic' command in Junos?

Accepted Answer

It can filter packets using the 'matching' option to capture only specific traffic.. Option B is correct because the 'monitor traffic' command in Junos supports a 'matching' option that allows you to specify a filter (e.g., 'matching "icmp"') to capture only packets that match the given criteria, reducing noise and focusing on specific traffic types. Option C is correct because 'monitor traffic interface <interface-name>' captures packets on a specified interface and displays them in real-time, which is useful for live troubleshooting.

Answer

It captures packets from the Routing Engine only.

Answer

It requires a reboot to start capturing packets.

Answer

It reads packets from a previously saved pcap file.

Question 19

Refer to the exhibit. A network engineer sees repeated 'PFE interrupt error' messages in the log for fpc0. What is the most likely impact and recommended action?

Accepted Answer

Replace the line card (FPC0) as it is experiencing hardware failures causing traffic loss.. The 'PFE interrupt error' message indicates a hardware-level failure on the Packet Forwarding Engine (PFE) of FPC0. Since the PFE is responsible for forwarding packets, such errors typically cause traffic loss or drops. The recommended action is to replace the line card (FPC0) because persistent PFE interrupt errors are symptomatic of a hardware fault that cannot be resolved by software resets or upgrades.

Answer

Remove and reinsert the PIC on FPC0 to reseat the connection.

Answer

Restart the PFE process using 'restart pfe' command.

Answer

Perform a software upgrade on the router to fix a known bug.

Question 20

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.