JN0-106 Practice Test 2 — 25 Questions

Question 1

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?

Choose an answer to begin — your selection is scored in the full session.

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

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 15

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

Question 16

An administrator is asked to check the system log files for any error messages related to interface failures. Which command would be most efficient?

Accepted Answer

show log messages. 'show log messages' is the standard JUNOS command to display the contents of the /var/log/messages file. While it does not include a filter, it is the only valid command among the options that allows the administrator to view existing system log messages. The other options are either invalid commands (B and D) or used for real-time monitoring (A), which is not efficient for checking historical log files.

Answer

monitor start messages | match "error"

Answer

show log file messages | match "error"

Answer

show system syslog messages

Question 17

A network administrator accidentally deleted a vital part of the configuration while in configuration mode. They need to revert to the previous configuration without losing recent changes that are correct. Which action should they take?

Accepted Answer

rollback 0. The 'rollback 0' command reverts the candidate configuration to the most recently committed configuration (the current active configuration), discarding any uncommitted changes. This allows the administrator to undo the accidental deletion without affecting any recently committed correct changes, as those are already part of the active configuration. Option B, 'rollback 1', would revert to the previous commit, which could remove recently committed correct changes if they were made in the most recent commit. Therefore, 'rollback 0' is the safer choice when you want to preserve correct changes that have already been committed.

Answer

deactivate

Answer

rollback 1

Answer

delete

Question 18

An engineer configures two static routes to 172.16.0.0/16 with next-hops 10.0.1.1 and 10.0.2.1, both with the same preference and same metric. How does Junos handle traffic to this prefix?

Accepted Answer

It load balances via ECMP.. Junos uses Equal-Cost Multipath (ECMP) when multiple static routes to the same destination prefix have identical preference (administrative distance) and metric. Since both routes to 172.16.0.0/16 have the same preference (default 5 for static routes) and metric (0 by default), Junos installs both in the forwarding table and load-balances traffic across the two next-hops (10.0.1.1 and 10.0.2.1) per-flow or per-packet depending on the configured hash algorithm.

Answer

It uses active/passive selection.

Answer

It uses only the first configured route.

Answer

It drops traffic due to ambiguity.

Question 19

An administrator wants to drop traffic destined to the 10.10.10.0/24 network without sending an ICMP unreachable message back to the source. Which static route option should be used?

Accepted Answer

discard. The 'discard' static route option silently drops traffic destined to the 10.10.10.0/24 network without generating any ICMP unreachable message. This is in contrast to the 'reject' option, which drops traffic but sends an ICMP unreachable back to the source. The 'discard' route is ideal for blackholing unwanted traffic while avoiding unnecessary network feedback.

Answer

reject

Answer

next-table

Answer

resolve

Question 20

Refer to the exhibit. Why is the route via 10.0.0.1 selected as the active route?

Accepted Answer

It has a lower preference. In Junos, the active route is selected based on the route preference value, where a lower preference is preferred. Since the route via 10.0.0.1 has a lower preference than the other route, it is chosen as active. This is a fundamental Junos routing decision process, distinct from metrics which are used within a single routing protocol.

Answer

It has a lower metric

Answer

It has a lower cost

Answer

It is an older route