JN0-106 Practice Test 5 — 25 Questions

Question 1

A network engineer is troubleshooting a connectivity issue and wants to see the active routes in the routing table. Which Junos CLI command should they use?

Accepted Answer

show route. The 'show route' command displays the active routing table entries, including directly connected, static, and dynamic routes learned via protocols like OSPF, BGP, or IS-IS. This is the correct command to view the active routes the device uses for forwarding traffic.

Answer

show log messages

Answer

show configuration

Answer

show interface

Question 2

While in configuration mode, an administrator wants to see the difference between the candidate configuration and the active configuration. Which command accomplishes this?

Accepted Answer

show | compare. The 'show | compare' command, when executed in configuration mode, displays the differences between the candidate configuration and the active (committed) configuration. This pipe filter compares the current candidate configuration against the last committed configuration, highlighting additions, deletions, and changes, which is the exact requirement for seeing the difference.

Answer

show configuration

Answer

run show configuration

Answer

show system commit

Question 3

A network operator needs to backup the current configuration to a file on the local flash. Which command accomplishes this?

Accepted Answer

show configuration | save /var/tmp/backup.conf. The correct command to backup the current configuration from operational mode is `show configuration | save /var/tmp/backup.conf`. This pipes the active configuration to the save command, writing it to the specified file. Option B (`save /var/tmp/backup.conf`) is a configuration mode command and will not work in operational mode. Option A saves the rescue configuration, not the active configuration. Option C commits the configuration and exits but does not save to a file.

Answer

request system configuration rescue save

Answer

save /var/tmp/backup.conf

Answer

commit and-quit

Question 4

Your enterprise network uses Juniper EX4300 switches in a collapsed core design with RSTP (802.1w) as the Layer 2 loop prevention protocol. You add a new EX2300 switch to an access closet and connect it to two different core switches using two uplink interfaces configured in an LACP LAG. After connecting the new switch, you notice intermittent connectivity issues across the entire network, with some devices reporting temporary packet loss. The issue occurs sporadically, especially during configuration changes or when links flap. You suspect the problem is related to RSTP. Upon investigation, you see that the new switch's uplink interfaces are both in the forwarding state, but occasionally one of them transitions to blocking and then back to forwarding. What is the most likely cause of the intermittent issues?

Accepted Answer

The LAG is not recognized as a single logical link by RSTP, causing RSTP to see two separate links and create a loop. B is correct because the two uplinks are connected to two different core switches. A standard LACP LAG requires both links to terminate on the same remote switch. Since they terminate on different switches, the LAG does not form and RSTP sees two separate physical links. This creates a loop between the EX2300 and the core (via the core switches' interconnection), so RSTP blocks one link. When configuration changes or link flaps occur, RSTP recalculates and the blocked port can temporarily transition to forwarding, causing intermittent packet loss.

Answer

The LACP system priority is set too low on the new switch, causing it to lose LACP negotiations

Answer

The uplink interfaces are configured as alternate ports instead of root ports

Answer

The new switch has a different root bridge priority, causing it to become the root and disrupting topology

Question 5

A Junos device has multiple configuration files saved. Which command shows the available rollback configurations?

Accepted Answer

show system commit. The 'show system commit' command displays a list of all committed configuration revisions, including their commit IDs and timestamps, which are used to roll back to a previous configuration. The rollback feature in Junos relies on these stored commit files, and the command explicitly shows the available rollback points.

Answer

show system configuration

Answer

show system rollback

Answer

show configuration | display rollback

Question 6

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 7

You are a network administrator for a large enterprise. You have a Juniper SRX firewall that is used as the primary internet gateway. Users are reporting that they are unable to access certain external websites. You check the device and find that the security policies appear correct, and the routing is in place. You suspect that the issue might be related to the DNS resolution. You want to verify that the device can resolve DNS names and that the DNS server configuration is correct. Which command should you use to test DNS resolution from the Juniper device?

Accepted Answer

ping <external website FQDN>. The `ping` command with a fully qualified domain name (FQDN) forces the Juniper device to perform a DNS resolution before sending ICMP echo requests. If the device cannot resolve the FQDN, the ping will fail with a 'hostname not found' error, directly indicating a DNS configuration or reachability issue. This tests both the DNS server configuration and the device's ability to resolve names, which is essential for verifying DNS functionality.

Answer

show system connections

Answer

traceroute <external website FQDN>

Answer

show dns name-server

Question 8

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 9

Your data center uses Juniper QFX5110 switches as leaf nodes in a Virtual Chassis Fabric (VCF) topology with QFX5100 as spine nodes. You are adding a new QFX5110 leaf node to the fabric. The new switch is physically connected to all spine nodes as per the cabling guidelines. However, after powering on the new switch, it does not automatically join the fabric. The existing fabric shows the new switch's member ID as 8, but it remains in 'standalone' state. The VCF has been operational for several months without issues. You check the configuration on the existing VC and notice that the 'virtual-chassis' configuration does not include the new member. What is the most likely reason the new switch does not join?

Accepted Answer

The new switch does not have the same virtual-chassis ID configured as the existing fabric. In a Virtual Chassis Fabric (VCF), all member switches must share the same virtual-chassis ID to be recognized as part of the same fabric. The existing fabric has a configured virtual-chassis ID, but the new QFX5110, by default, has a different or no virtual-chassis ID set. Without a matching virtual-chassis ID, the new switch cannot join the fabric and remains in 'standalone' state, even though it is physically connected and assigned a member ID.

Answer

The new switch is running a different version of Junos that is not compatible with the fabric

Answer

The new switch is only connected to one spine node, and VCF requires full mesh connections to all spines

Answer

The new switch has 'set virtual-chassis no-split-detection' enabled, preventing it from joining

Question 10

A router has two ISIS adjacencies to the same router, both with equal metrics. The router installs both routes in the routing table and performs load balancing. The network team wants to verify that both next-hops are being used for a particular destination. Which command provides this information?

Accepted Answer

`show route forwarding-table destination 10.0.0.0/24`. The `show route forwarding-table destination 10.0.0.0/24` command displays the actual forwarding entries in the Packet Forwarding Engine (PFE), including all next-hops used for load balancing. Unlike the routing table, the forwarding table shows which next-hops are actively installed and used for forwarding traffic, making it the definitive command to verify equal-cost multipath (ECMP) usage.

Answer

`show route 10.0.0.0/24 extensive`

Answer

`show route protocol isis`

Answer

`show route 10.0.0.0/24 detail`

Question 11

A network engineer is troubleshooting connectivity between two directly connected Juniper routers. The interface on Router A shows 'up' but no packets are being received from Router B. Which command should the engineer use on Router A to check if the interface is expecting to receive a specific encapsulation type?

Accepted Answer

show interfaces extensive. The 'show interfaces extensive' command displays detailed interface information, including the encapsulation type configured on the interface. If Router A expects a specific encapsulation (e.g., PPP, HDLC, or Ethernet) that does not match what Router B is sending, the interface will show 'up' but will not receive packets. This command allows the engineer to verify the configured encapsulation type. Option B is incorrect because 'show interfaces terse' provides a concise summary (name, status, protocol, and address) but does not include encapsulation details.

Answer

show interfaces terse

Answer

show configuration interfaces

Answer

monitor traffic interface

Question 12

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 13

Your Juniper router is running OSPF with multiple neighbors. You have a prefix 10.10.10.0/24 that is being learned via OSPF from two different routers: Router A with metric 30 and Router B with metric 20. The OSPF route from Router B is active. You want to ensure that traffic to 10.10.10.0/24 uses the path through Router A instead, even though it has a higher metric. You cannot change the OSPF metric on Router A. Which action should you take?

Accepted Answer

Use a routing policy to increase the preference of the OSPF route from Router B.. In JUNOS, route preference (administrative distance) determines which route is installed in the routing table when multiple protocols or sources provide the same prefix. By default, OSPF internal routes have a preference of 10. You can use a routing policy to increase the preference of the OSPF route from Router B (making it less preferred), which will cause the route from Router A (with its default preference of 10) to become active, even though its metric is higher. This approach does not require changing the OSPF metric or removing the route from Router A.

Answer

Increase the metric on Router B for that prefix.

Answer

Use a routing policy to reject the OSPF route from Router A.

Answer

Configure a static route to 10.10.10.0/24 pointing to Router A.

Question 14

A static route to 10.0.0.0/8 has next-hop 192.168.1.1. The route is not installed in the routing table. Which condition must be met for the route to become active?

Accepted Answer

The next-hop 192.168.1.1 must be reachable via an active route (e.g., a direct or OSPF route).. For a static route to be installed in the Junos routing table, its next-hop must be reachable via an active route in the routing table. This is because Junos performs recursive next-hop resolution: it looks up the next-hop IP address (192.168.1.1) in the routing table and requires a valid, active route (e.g., a directly connected or OSPF-learned route) to that address. Without this, the static route remains hidden and is not installed.

Answer

The static route must have a lower preference than any dynamic route to the same prefix.

Answer

The next-hop must have an ARP entry in the ARP table.

Answer

The metric of the static route must be lower than that of any other route to the same prefix.

Question 15

A network engineer is troubleshooting OSPF adjacencies between two Juniper routers. The routers are directly connected and have matching OSPF configurations except for the router IDs. Router A has router-id 10.0.0.1, Router B has router-id 10.0.0.2. The adjacency remains in the EXSTART state. What is the most likely cause?

Accepted Answer

The MTU on the interface is mismatched.. The EXSTART state indicates that the routers have progressed past the 2-Way state and are attempting to exchange Database Description (DBD) packets. A common cause for getting stuck in EXSTART is an MTU mismatch, because OSPF uses the interface MTU to determine the maximum size of DBD packets. If Router A's MTU is larger than Router B's, Router B will drop the oversized DBD packet and the adjacency will remain in EXSTART.

Answer

The router IDs are not the same.

Answer

The area ID is not configured.

Answer

The hello and dead intervals are mismatched.

Question 16

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 17

A technician notices that the /var partition on a Junos device is 95% full. Which action will immediately free up disk space without affecting device operation?

Accepted Answer

Clear log files using 'clear log messages'. The 'clear log messages' command immediately removes the contents of the active log files (e.g., messages, interactive-commands) without requiring a reboot or affecting running processes. This directly frees up space in /var/log, which is a primary consumer of the /var partition, while leaving the directory structure intact so logging continues normally.

Answer

Delete unused software packages using 'request system software delete'

Answer

Reboot the device

Answer

Remove the /var/log directory

Question 18

A network administrator notices that traffic between two VLANs is not reaching its destination. The switch has an IRB interface configured with an IP address in each VLAN's subnet. What is the most likely missing configuration?

Accepted Answer

The VLANs are not defined on the switch.. The IRB interface provides Layer 3 routing between VLANs, but it requires the VLANs themselves to be defined on the switch. If the VLANs are not defined, the switch cannot associate the IRB interface with the correct broadcast domains, and traffic will not be forwarded between them. Option C correctly identifies this missing configuration.

Answer

The IRB interface does not have an IP address configured.

Answer

The VLANs are on different switches.

Answer

The switch ports are not configured for VLAN tagging.

Question 19

A network administrator is configuring a new interface and wants to ensure that the interface is enabled and can pass traffic. Which configuration element is required?

Accepted Answer

set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24. In Junos, an interface is administratively enabled by default (no explicit 'enable' command is needed), but to pass traffic it requires a logical unit with a configured protocol family and an IP address. The command 'set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24' creates unit 0, assigns the IPv4 address, and implicitly enables the interface for traffic forwarding. Without an address under a family, the interface cannot pass IP traffic even if it is administratively up.

Answer

set interfaces ge-0/0/0 enable

Answer

set interfaces ge-0/0/0 unit 0 family inet

Answer

set interfaces ge-0/0/0 disable

Question 20

What happens when a user issues the 'request system reboot' command without any options?

Accepted Answer

The device prompts for confirmation.. When a user issues the 'request system reboot' command without any options, Junos OS prompts for confirmation before proceeding. This is a safety mechanism to prevent accidental reboots, as the command does not automatically reboot the device immediately or schedule a delayed reboot by default.

Answer

The device reboots after the current commit.

Answer

The device reboots immediately.

Answer

The device schedules a reboot in 5 minutes.