JN0-106 Junos OS Fundamentals — 25 Questions

Question 1

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?

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

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 2

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 3

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 4

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 5

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 6

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 7

Which THREE of the following statements are true regarding Junos OS commit operations?

Accepted Answer

The 'commit check' command validates the candidate configuration without activating it.. Option A is correct because 'commit check' performs a syntax and semantic validation of the candidate configuration against the schema without making it the active configuration, so errors are reported but nothing is activated. Option B is correct because the 'commit' command merges the candidate configuration into the active configuration and activates it on the device. Option C is correct because 'commit confirmed' activates the candidate configuration but starts a rollback timer (default 10 minutes); if the operator does not issue a confirming 'commit' before the timeout, Junos automatically reverts to the previous active configuration. Option D is not marked correct because although Junos supports commit scripts, they are configured and executed as part of the commit process rather than being run multiple times arbitrarily during a single commit. Option E is not marked correct because 'rollback' reverts the candidate configuration to a previously committed configuration (rollback 0 being the current active one), not to the current active configuration itself.

Answer

You can run multiple commit scripts during a single commit operation.

Answer

The rollback command reverts to the current active configuration.

Question 8

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 9

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 10

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 11

Order the steps to configure a user account with a password in Junos.

Accepted Answer

Set the class (set system login user class ), then set the authentication method to plain-text-password (set system login user authentication plain-text-password), then commit the configuration.. The correct order to configure a user account in Junos involves setting both the class and authentication before committing. Options A and B are both valid sequences because the order of setting the class and authentication does not matter; the configuration is applied only upon commit. Option C is wrong because committing before setting the authentication leaves the user without a password. Option D is wrong because committing before setting the class results in an incomplete user configuration with no privilege level.

Answer

Set the class, commit the configuration, then set the authentication method to plain-text-password.

Answer

Set the authentication method to plain-text-password, commit the configuration, then set the class.

Question 12

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 13

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 14

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 15

Refer to the exhibit. How many commits have been made on this device?

Accepted Answer

3. The exhibit shows the output of the 'show system commit' command, which lists each commit made on the device. The output displays three entries, each with a unique commit number (0, 1, 2), indicating that three commits have been performed. Therefore, option A is correct.

Answer

1

Answer

2

Answer

0

Question 16

Which TWO statements are true about the Junos OS boot process?

Accepted Answer

The routing engine initializes after the kernel loads.. Option A is correct because in the Junos OS boot sequence, the kernel is loaded and started first, and only after the kernel initializes does the Routing Engine (RE) software, including the Junos daemons such as mgd and rpd, begin to initialize. Option D is correct because the boot loader (for example, the U-Boot or BIOS/GNU GRUB stage depending on platform) is responsible for locating and loading the kernel image from the boot device (such as the internal flash or disk) into memory before execution is handed to the kernel. Options B, C, and E are not correct: the forwarding engine (PFE) is initialized after the kernel and RE come up, not before the kernel; the configuration is loaded from /config by the Junos management daemon after the kernel and RE software are running, not before the kernel starts; and while the kernel does mount the root file system, that statement is not one of the two marked correct answers for this question.

Answer

The forwarding engine is initialized before the kernel.

Answer

The configuration is loaded from /config before the kernel starts.

Answer

The kernel mounts the root file system.

Question 17

Which operational command displays the system's current time and date?

Accepted Answer

show system uptime. The correct command to display the system's current time and date in Junos is 'show system uptime'. This command outputs the current time and date, along with how long the system has been running (uptime), the number of users, and the load averages. It is the standard operational command for checking the system clock on Juniper devices.

Answer

show system time

Answer

show system inventory

Answer

show system processes

Question 18

A device is configured with multiple routing instances. An engineer needs to view the ARP table for a specific routing instance. Which command should be used?

Accepted Answer

show arp instance . The `show arp instance ` command is the Junos OS syntax to display the ARP table for a specific routing instance. In Junos, routing instances create separate forwarding tables, and the ARP cache is per-instance; this command targets the instance's ARP entries directly.

Answer

show arp routing-instance <instance-name>

Answer

show arp

Answer

show route table <instance-name>.inet.0

Question 19

Which TWO statements about the Junos commit model are true?

Accepted Answer

A commit makes the candidate configuration the active configuration.. Option A is correct because in the Junos commit model, the commit command merges the candidate configuration into the active configuration (the running config used by the device), making the candidate the active configuration. Option C is correct because the rollback command reverts the active configuration to a previously committed configuration (e.g., rollback 1 restores the last committed config, rollback 0 restores the current active config), which is a core part of Junos configuration recovery. Option B is wrong because discarding changes is done with the 'rollback 0' or 'rollback' command (or 'discard' in some contexts), not commit; commit applies changes. Option D is wrong because commit validation is not automatic before every commit—validation is performed when you run 'commit check' or when using 'commit and-quit' with validation, but a standard commit does not automatically run a separate validation step. Option E is wrong because Junos supports only one candidate configuration at a time per routing instance; multiple candidates cannot be active simultaneously.

Answer

The commit command is used to discard changes.

Answer

A commit validation is performed automatically before commit.

Answer

Multiple candidates can be active simultaneously.

Question 20

Which THREE steps are typically part of a Junos OS upgrade process?

Accepted Answer

Add the image using the request system software add command.. Option B is correct because the Junos upgrade begins by loading the new software image onto the device with the request system software add command, which installs the package into the alternate partition or the requested partition. Option D is correct because after adding the image you validate it, typically with request system software validate, to confirm the package is intact and compatible before rebooting. Option E is correct because the new image only becomes active after a reboot, which switches the device to the newly installed software. Option A is not a typical upgrade step, since the previous image is normally retained for rollback rather than removed. Option C is not part of the upgrade itself, because committing the configuration applies configuration changes, not the software image installation.

Answer

Remove the previous image.

Answer

Commit the configuration.