JN0-106 Junos OS Fundamentals — 50 Questions

Question 1

A network engineer is configuring a new Juniper device and needs to ensure that the configuration is saved persistently across reboots. Which command should be used?

Accepted Answer

commit. The `commit` command activates the candidate configuration and saves it to the active configuration database, ensuring it persists across reboots. Without a commit, any changes made in candidate mode are lost when the device restarts.

Answer

save

Answer

request system reboot

Answer

show configuration

Question 2

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 3

A Juniper device is experiencing high CPU utilization due to a routing protocol process. The engineer suspects a specific BGP peer is causing the issue. Which operational command can be used to collect diagnostic information about the routing protocol processes?

Accepted Answer

show system processes extensive. 'show system processes extensive' displays detailed CPU and memory usage for each individual process, including routing protocol daemons like bgpd. This allows the engineer to see which routing protocol process (e.g., bgpd) is consuming excessive CPU resources. However, it does not identify a specific BGP peer; further investigation with commands like 'show bgp neighbor' would be needed to isolate the peer.

Answer

request support information

Answer

show bgp summary

Answer

monitor traffic interface

Question 4

An engineer needs to view the current active configuration on a Juniper device. Which command will display the configuration that is currently running?

Accepted Answer

show configuration. The 'show configuration' command displays the current active configuration that is committed and running on a Juniper device. Unlike Cisco's 'show running-config', Junos uses a commit model where the candidate configuration is activated only after a 'commit' operation, and 'show configuration' shows that committed, active configuration.

Answer

show chassis hardware

Answer

show interfaces terse

Answer

show system commit

Question 5

During a maintenance window, an engineer needs to apply a series of configuration changes that are stored in a text file. Which command sequence should be used to load and apply the changes from the file?

Accepted Answer

configure; load merge /var/tmp/changes.txt; commit. The engineer needs to enter configuration mode (configure) and then use the 'load merge' command to merge the contents of the text file into the candidate configuration without replacing the entire configuration. The 'commit' command then activates the changes. This is the standard Junos workflow for applying incremental changes from a file.

Answer

request system configuration rescue save

Answer

load override /var/tmp/changes.txt; commit

Answer

configure; load patch /var/tmp/changes.txt; commit

Question 6

An engineer notices that a Juniper device is not saving configuration changes across reboots. What is the most likely cause?

Accepted Answer

The candidate configuration was not committed.. In Junos OS, configuration changes are stored in a candidate configuration and only become active and persistent across reboots after a 'commit' operation. Without a commit, the changes remain in the candidate buffer and are discarded upon reboot, causing the device to revert to the last committed configuration.

Answer

The rescue configuration is not set.

Answer

The device is booting from factory-default configuration.

Answer

The command 'request system reboot' was used instead of 'commit'.

Question 7

Which TWO statements are true about the Junos OS candidate configuration model? (Choose two.)

Accepted Answer

The candidate configuration can be modified without affecting the active configuration.. The Junos OS candidate configuration model allows modifications to be made to a separate candidate configuration file without affecting the active configuration currently running on the device. This ensures that changes can be staged, reviewed, and validated before being committed, providing a safe and non-disruptive way to manage configuration changes.

Answer

Each change is applied incrementally to the active configuration.

Answer

The candidate configuration is stored in a separate file from the active configuration.

Answer

After a commit, the candidate configuration is automatically discarded.

Question 8

Which THREE commands are valid Junos operational mode commands for monitoring network diagnostics? (Choose three.)

Accepted Answer

traceroute. The 'traceroute' command in Junos operational mode sends a series of UDP packets with increasing TTL values to discover the path a packet takes to a destination, which is a standard network diagnostic tool. It is a valid operational mode command used for monitoring network connectivity and path analysis.

Answer

show configuration

Answer

request system reboot

Question 9

Which TWO statements correctly describe the function of the 'commit' command in Junos OS? (Choose two.)

Accepted Answer

It validates the candidate configuration for syntax errors.. The 'commit' command in Junos OS first validates the candidate configuration for syntax errors before applying it. If syntax errors are found, the commit fails and the candidate configuration is not applied, ensuring the device does not enter an inconsistent state. This validation step is a core part of Junos's transactional configuration model, where changes are staged in a candidate configuration and then committed atomically.

Answer

It schedules the configuration to be applied at a later time.

Answer

It discards the candidate configuration after saving.

Answer

It automatically reboots the device to apply the changes.

Question 10

Based on the exhibit, what is the most likely reason for the ping failure?

Accepted Answer

The neighbor device is not configured or is unreachable.. The ping failure is most likely due to the neighbor device not being configured or unreachable because the output shows the interface is up (Physical link is Up) and the unit is enabled (Unit 0 is enabled), but there is no neighbor discovery or ARP entry. Without a valid next-hop or neighbor reachability, ICMP echo requests cannot be forwarded, resulting in ping failure.

Answer

A firewall filter is blocking ICMP traffic.

Answer

The interface is disabled at the unit level.

Answer

The interface is administratively down.

Question 11

You are a network engineer at a service provider. You have a Juniper MX router that serves as a BGP route reflector for a large number of customer routes. Recently, the router has been experiencing high CPU utilization, and the BGP process (rpd) is consuming excessive memory. You suspect that the router is receiving too many routes from a specific BGP peer, causing the routing table to grow beyond the available memory. You need to diagnose the issue without affecting production traffic. Which course of action should you take?

Accepted Answer

Use the 'show bgp summary' command to check the number of prefixes per peer.. The 'show bgp summary' command displays the number of prefixes received from each BGP peer, allowing you to identify which peer is advertising an excessive number of routes. This directly addresses the suspicion of a specific peer and is non-disruptive to production traffic.

Answer

Immediately shut down all BGP peers to stop the influx of routes.

Answer

Configure a prefix limit on all BGP peers.

Answer

Use the 'show route summary' command to check the routing table size and memory usage.

Question 12

A network engineer notices that a Junos device is not forwarding traffic for a specific subnet. The routing table shows the route for that subnet, but traffic is still not being forwarded. Which command should the engineer use to verify whether the firewall filter is dropping the traffic?

Accepted Answer

show firewall filter. To verify whether a firewall filter is dropping traffic, you need to inspect the packet counters for each filter term. The command 'show firewall filter' displays all firewall filter statistics, including packet/byte counts for terms with a discard action, allowing you to see if the drop counter is incrementing. 'show firewall filter log' is not a standard Junos command; the correct command for logs is 'show firewall log', and logs are only generated if the filter term explicitly includes a 'log' action. Therefore, the correct answer is C, not D.

Answer

show interfaces terse

Answer

show firewall filter counter

Answer

show firewall filter log

Question 13

Refer to the exhibit. An engineer wants to verify that static routes for 10.0.1.0/24 and 10.0.2.0/24 are present in the routing table. Based on the output, which statement is true?

Accepted Answer

Both routes are active and have the same preference value.. The output shows both 10.0.1.0/24 and 10.0.2.0/24 as static routes with a preference of 5. Since the preference value is the same and both are listed as active (the 'A' flag is present in the routing table), both routes are installed and active in the forwarding table. In Junos, a static route's default preference is 5, and any route with a lower preference is preferred; here both have equal preference, so they coexist as active routes.

Answer

Both routes have a preference of 0.

Answer

Only the 10.0.1.0/24 route is active.

Answer

Both routes use the same next-hop IP address.

Question 14

A network engineer needs to check the operational status of all interfaces on a Juniper device. Which command provides a summary of interface status including link state, protocol state, and error counters?

Accepted Answer

show interfaces. The 'show interfaces' command provides a detailed summary of all interfaces, including administrative status, link state, protocol state, and error counters. It displays a comprehensive view of interface operational status, which meets the engineer's requirement for error counters. Option C (show interfaces terse) gives a concise summary but does not include error counters.

Answer

show configuration interfaces

Answer

show interfaces terse

Answer

show interface descriptions

Question 15

Refer to the exhibit. How many next hops are configured for the 192.168.1.0/24 route?

Accepted Answer

2. The route 192.168.1.0/24 has two next hops configured: one via 10.0.0.2 and another via 10.0.0.3. This is a case of equal-cost multipath (ECMP) routing, where Junos installs multiple next hops for the same prefix to load-balance traffic across multiple paths.

Answer

0

Answer

3

Answer

1

Question 16

Match each Junos file system directory to its content.

Accepted Answer

/config: Contains active configuration files. These are key directories in the Junos file system. Correct matches: /config (configuration), /var (variable data), /tmp (temporary). Common confusions involve /altroot and /packages.

Answer

/altroot: Contains software packages

Answer

/packages: Backup root filesystem

Question 17

Which command displays the current hostname of a Junos device?

Accepted Answer

show system host-name. The command 'show system host-name' is the correct operational mode command to display the current hostname configured on a Junos device. It retrieves the hostname from the active configuration and displays it in the output, confirming the device's identity on the network.

Answer

show chassis hardware

Answer

show configuration system host-name

Answer

show system uptime

Question 18

An administrator needs to grant a user read-only access to the device via SSH. Which configuration should be applied?

Accepted Answer

set system login user guest class read-only. The 'read-only' class in Junos provides exactly the required level of access: users can view configuration and operational data but cannot make any changes. The 'set system login user guest class read-only' command assigns the predefined 'read-only' login class to the user 'guest', which permits SSH login with read-only privileges. This matches the administrator's requirement precisely.

Answer

set system login user admin class operator

Answer

set system login user readonly class super-user

Answer

set system login user guest class operator

Question 19

Which command is used to view the terminal history of commands entered by the user?

Accepted Answer

show cli history. The 'show cli history' command displays the list of previously entered CLI commands in the current session, allowing users to recall and re-execute them. This is a Junos-specific command that provides a terminal history feature, distinct from the commit history or system logs.

Answer

show system commit

Answer

show configuration

Answer

show log messages

Question 20

An engineer suspects that a recent software upgrade caused a compatibility issue. Which command should be used to revert the Junos OS to the previous version?

Accepted Answer

request system software rollback. The 'request system software rollback' command is the correct method to revert the Junos OS to the previously installed version. This command triggers a reboot and loads the previous software set from the /altroot partition, effectively undoing the upgrade while preserving the configuration.

Answer

rollback 0

Answer

request system reboot

Answer

request system software delete jinstall-*.tgz