JN0-106 Practice Exam 2 — 20 Questions

Question 1

An administrator wants to see the differences between the candidate configuration and the active configuration. Which command should be used?

Accepted Answer

show | compare. The 'show | compare' command displays the differences between the candidate configuration and the active (committed) configuration. This is the standard Junos method for reviewing uncommitted changes before committing them, as it outputs a diff-style output showing lines added, deleted, or modified.

Answer

show | display set

Answer

run show configuration

Answer

show configuration

Question 2

A junior admin tries to commit a configuration but receives a 'commit error: syntax error' message. They suspect a missing closing brace. Which CLI command helps identify the exact line with the error?

Accepted Answer

commit check. The 'commit check' command validates the candidate configuration for syntax errors without committing it. When a syntax error like a missing closing brace is present, commit check outputs the exact line number and file where the error occurs, allowing the admin to locate and fix the issue before attempting a commit again.

Answer

rollback 0

Answer

load merge

Answer

show configuration

Question 3

An engineer wants to view system log messages as they are generated in real-time. Which command should they use?

Accepted Answer

monitor log messages. The 'monitor log messages' command in Junos OS provides a real-time view of system log messages as they are generated, similar to the 'tail -f' command on Unix systems. It streams new log entries to the terminal without requiring manual refresh, making it ideal for live monitoring of events.

Answer

start log messages

Answer

request system log

Answer

show log messages

Question 4

A user wants to see all available commands starting with 'show'. Which key should they press after typing 'show'?

Accepted Answer

?. In the Junos CLI, pressing the '?' key after typing a partial command like 'show' displays a list of all available commands or options that start with that string. This is the standard context-sensitive help feature in Junos, which is distinct from other CLI behaviors.

Answer

Space

Answer

Tab

Answer

Ctrl-P

Question 5

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

Question 6

A technician is troubleshooting a device that has an inconsistent configuration. They need to revert to the configuration that was committed exactly two commits ago. Which command sequence accomplishes this?

Accepted Answer

rollback 2 followed by commit. The `rollback 2` command reverts the candidate configuration to the state it was in two commits ago, but the change is not applied until a `commit` is issued. This two-step sequence (rollback followed by commit) is required to make the reverted configuration active. Without the commit, the device continues running the current active configuration.

Answer

rollback 2

Answer

commit confirmed 2

Answer

rollback 3

Question 7

A network engineer needs to analyze NTP synchronization status and offset. Which command provides detailed NTP peer information including delay, offset, and jitter?

Accepted Answer

show ntp associations. The 'show ntp associations' command displays detailed NTP peer information, including delay, offset, and jitter, which are essential for analyzing synchronization status. This command lists all configured NTP peers and their current state, providing the specific metrics needed to assess clock accuracy and stability.

Answer

show ntp statistics

Answer

show ntp status

Answer

show ntp peer

Question 8

Refer to the exhibit. A frame with destination MAC 00:0c:29:2a:3b:4d arrives on interface ge-0/0/0. What action will the switch take?

Accepted Answer

Forward the frame out of ge-0/0/2 only. The switch learns MAC addresses and their associated VLANs from incoming frames. Since the destination MAC 00:0c:29:2a:3b:4d is already in the MAC address table and mapped to interface ge-0/0/2 within the same VLAN, the switch forwards the frame only out of ge-0/0/2. This is the fundamental behavior of transparent bridging: unicast frames are forwarded only to the port where the destination MAC was last seen.

Answer

Flood the frame to all ports except ge-0/0/0

Answer

Drop the frame because the VLAN does not match

Answer

Forward the frame out of both ge-0/0/1 and ge-0/0/2

Question 9

Refer to the exhibit. What will happen if the engineer commits this configuration?

Accepted Answer

The interface will support both IPv4 and IPv6 traffic.. The configuration shown includes both `family inet` and `family inet6` under the same interface. Junos allows multiple address families to coexist on a single interface, enabling the interface to process both IPv4 and IPv6 traffic simultaneously. This is a standard feature of Junos, not an error.

Answer

The interface will have two primary IP addresses.

Answer

The configuration will fail because inet and inet6 cannot coexist.

Answer

Only the family inet will be applied.

Question 10

Which command saves the current operational state information to a file that can be provided to Juniper support for troubleshooting?

Accepted Answer

request support information. The 'request support information' command collects a comprehensive snapshot of the current operational state, including configuration, logs, routing tables, and interface statistics, and packages it into a file (e.g., /var/tmp/support-info-date-time.tgz) that can be directly provided to Juniper support for troubleshooting. This is the standard Junos method for gathering diagnostic data.

Answer

monitor traffic

Answer

show system information

Answer

file copy

Question 11

You are troubleshooting an OSPF adjacency issue between two Juniper MX series routers, R1 and R2, both running Junos 18.2. They are directly connected via a Gigabit Ethernet link. R1's interface ge-0/0/0 is configured with IP 192.168.1.1/24, and R2's ge-0/0/0 is configured with IP 192.168.1.2/24. Both interfaces are in OSPF area 0.0.0.0. The physical connectivity is confirmed up, and both interfaces are administratively enabled. You have checked that the hello and dead intervals match (hello 10, dead 40), the area IDs are identical, and the subnet masks are /24. No firewall filters are blocking OSPF. The OSPF configuration on R1 includes 'authentication-type md5' and 'authentication-key juniper123' under the interface. On R2, the configuration also includes 'authentication-type md5' but the key is 'juniper321'. Both routers have loopback addresses as router IDs: 1.1.1.1 for R1 and 2.2.2.2 for R2. No explicit OSPF network type is set, so the default is broadcast. Despite these configurations, the OSPF adjacency state on both routers remains in INIT. What is the most likely cause of this issue?

Accepted Answer

The OSPF authentication keys do not match.. OSPF authentication keys must match exactly for the adjacency to form. R1 uses key 'juniper123' while R2 uses 'juniper321', causing the MD5 digest computed on each Hello packet to differ. Since OSPF authentication is validated per-packet, mismatched keys prevent the routers from moving past the INIT state.

Answer

The interface MTU size is mismatched.

Answer

The OSPF network type is mismatched.

Answer

The router IDs are not properly configured.

Question 12

Which TWO statements about the Junos CLI are correct?

Accepted Answer

The pipe character (|) can be used to filter command output.. Option B is correct because the pipe character (|) in the Junos CLI is used to filter or manipulate the output of show commands, for example with match, except, find, count, or display set. Option C is correct because from configuration mode the run command (or its abbreviation run) executes operational mode commands without leaving configuration mode, e.g., run show interfaces terse. Option A is incorrect because commit confirmed applies the candidate configuration temporarily and automatically rolls back after 10 minutes unless confirmed with a second commit, so it does not save permanently. Option D is incorrect because set cli screen-length 0 disables paging of output, not command-line editing features. Option E is incorrect because rollback 0 loads the currently active committed configuration, while rollback 1 reverts to the previous committed configuration.

Answer

The `commit confirmed` command saves the configuration permanently.

Answer

The `set cli screen-length 0` command disables command-line editing features.

Answer

The `rollback 0` command reverts to the previous committed configuration.

Question 13

During a network traffic storm, a Juniper EX switch's CPU utilization spikes to 100%. Which command would best help identify the cause?

Accepted Answer

monitor traffic interface ge-0/0/0. The 'monitor traffic interface' command captures live packet headers on the specified interface, allowing you to see the type and source of traffic causing the CPU spike. During a traffic storm (e.g., broadcast storm), this command reveals excessive broadcast, multicast, or unknown unicast frames, which are typically the root cause of high CPU utilization on Juniper EX switches.

Answer

show spanning-tree bridge

Answer

show ethernet-switching table

Answer

show interfaces extensive ge-0/0/0

Question 14

An administrator needs to quickly revert all uncommitted configuration changes and return the device to the last committed configuration. Which command accomplishes this?

Accepted Answer

rollback 0. The command 'rollback 0' reverts all uncommitted configuration changes and returns the device to the last committed configuration. In Junos, the rollback command uses a numeric argument to specify which previous configuration to load, with 0 always referring to the most recently committed configuration. This effectively discards any pending changes in the candidate configuration without requiring a commit.

Answer

delete configuration

Answer

load override

Answer

rollback 1

Question 15

An engineer is implementing VLAN trunking between two Juniper EX switches. Which statement about native VLANs on a trunk is correct?

Accepted Answer

Untagged frames arriving on a trunk port are assigned to the native VLAN.. On Juniper EX switches, a trunk port can accept both tagged and untagged frames. Untagged frames received on a trunk port are automatically assigned to the native VLAN, which by default is VLAN 1. This behavior is defined by the IEEE 802.1Q standard, where the native VLAN is the only VLAN that can carry untagged traffic on a trunk link.

Answer

The native VLAN cannot be changed after initial configuration.

Answer

Frames in the native VLAN are always tagged with the VLAN ID on the trunk.

Answer

The native VLAN must be the same as the management VLAN.

Question 16

Which TWO commands can be used to view the current operational state of an interface? (Choose two.)

Accepted Answer

show interfaces extensive. The 'show interfaces extensive' command displays detailed operational state information, including current status, errors, and statistics. The 'show interfaces terse' command provides a concise operational view showing interface names, administrative status, link status, and protocol families. Both commands query the current operational state of interfaces from the Junos OS kernel.

Answer

show log

Answer

show configuration interfaces

Answer

show route

Question 17

A network engineer needs to view the operational status of all interfaces on a Junos device, including those that are disabled. Which command should be used?

Accepted Answer

show interfaces terse. The 'show interfaces' command displays detailed information for all interfaces, including those that are administratively disabled. However, 'show interfaces terse' provides a concise, one-line-per-interface summary that is more efficient for quickly viewing the operational status of all interfaces, including disabled ones. For the JNCIA exam, 'show interfaces terse' is the recommended command for this purpose because it offers a clear and compact overview of interface status across the device.

Answer

show interfaces

Answer

show configuration interfaces

Answer

monitor interface traffic

Question 18

What is the primary function of the fxp0 interface on a Juniper device?

Accepted Answer

Management interface. The fxp0 interface is a dedicated out-of-band management Ethernet port on Juniper devices, used exclusively for management traffic such as SSH, SNMP, and syslog. It is separate from the data plane and control plane forwarding interfaces, ensuring administrative access remains available even if the routing or forwarding planes are disrupted.

Answer

Internal routing

Answer

Loopback testing

Answer

Data plane forwarding

Question 19

An enterprise uses OSPF across multiple areas. To reduce routing table size in the backbone area, the engineer wants to advertise a single summary route for all subnets in area 2. Which configuration is appropriate?

Accepted Answer

Configure 'area 2 area-range 10.0.0.0/16' on the ABR. The 'area-range' command on an Area Border Router (ABR) allows you to summarize a set of routes from a specific area into the backbone (area 0) by advertising a single aggregate route (e.g., 10.0.0.0/16) instead of all individual subnets. This reduces the routing table size in area 0 while still providing reachability to all subnets in area 2.

Answer

Configure a virtual-link between area 2 and area 0

Answer

Configure a default route from area 2 using 'default-metric'

Answer

Use a static route for the summary and redistribute it into OSPF

Question 20

A network administrator configures a default route using 'set routing-options static route 0.0.0.0/0 next-hop 10.0.0.1 preference 10' and later enables OSPF which also advertises a default route with default preference 150. Which route becomes active in the routing table?

Accepted Answer

Static route to 0.0.0.0/0 with next-hop 10.0.0.1. The static route has a preference of 10, which is lower than OSPF's default preference of 150. Junos uses the route with the lowest preference value as the active route in the routing table. Therefore, the static default route becomes active.

Answer

Neither route becomes active due to conflicting protocols

Answer

Both routes are active for ECMP load balancing

Answer

OSPF route to 0.0.0.0/0