JN0-106 Junos OS Fundamentals Practice Test 6 — 15 Questions

Question 1

Refer to the exhibit. An administrator wants to see authentication-related logs like SSH logins. In the current configuration, which log file contains this information?

Accepted Answer

messages. In Junos, authentication-related logs such as SSH login attempts are recorded by default in the 'messages' log file. This file captures syslog messages for various system events, including authentication successes and failures. The 'interactive-commands' log file only logs user-executed CLI commands after successful login, not the authentication process itself. The 'security' log is intended for firewall and security policy events, and 'utmp' is for user accounting. Therefore, option D is correct.

Answer

utmp

Answer

interactive-commands

Answer

security

Question 2

A company wants to implement best practice for password recovery on Juniper devices to avoid service disruption. Which of the following is the recommended method?

Accepted Answer

Boot the device into single-user mode from the console and reset the root password. Booting the device into single-user mode from the console is the standard, secure method for password recovery on Juniper devices. This process allows an administrator with physical console access to reset the root password without affecting the running configuration or causing service disruption, as the device boots with a minimal kernel and does not load the full configuration.

Answer

Perform a factory reset to default configuration

Answer

Use SNMP to modify the password field in the configuration

Answer

Contact JTAC to remotely reset the password

Question 3

An administrator notices that after committing a configuration change on a Juniper MX router, the device loses connectivity to the management network. The management interface is part of a dedicated management routing instance. Which of the following is the most likely cause?

Accepted Answer

The routing instance for the management interface was accidentally removed. The management interface is part of a dedicated management routing instance (often named mgmt_junos). If this routing instance is accidentally removed during a commit, the management interface loses its routing context and becomes unreachable, causing loss of connectivity to the management network. This is a common misconfiguration when an administrator modifies routing instance configurations without realizing the management interface depends on it.

Answer

A firewall filter was applied to the management interface that blocks all traffic

Answer

NTP was configured with an incorrect server address

Answer

A syslog server was configured that is unreachable

Question 4

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 5

What is the purpose of the 'commit confirmed' command in Junos OS?

Accepted Answer

It allows the administrator to test a configuration change with automatic rollback if confirmation is not received. The 'commit confirmed' command in Junos OS applies a candidate configuration change and starts a confirmation timer (default 10 minutes). If the administrator does not issue a 'commit' command before the timer expires, the system automatically rolls back to the previous active configuration. This allows safe testing of changes, especially over remote connections, preventing lockout if the change breaks connectivity.

Answer

It compares the candidate configuration with the active configuration

Answer

It permanently saves the candidate configuration to the startup configuration

Answer

It confirms that a previous commit was successful

Question 6

Which TWO statements about the Junos OS configuration hierarchy are correct? (Choose two.)

Accepted Answer

Configuration is organized in a hierarchical structure with levels. Option C is correct because Junos OS stores its configuration in a hierarchical tree structure organized into levels (such as system, interfaces, protocols), which is the defining characteristic of the Junos configuration model. Option E is correct because within that hierarchy, each level can hold one or more statements or values, allowing multiple configuration elements to be nested under a given hierarchy node. Option A is incorrect because Junos does not store configuration as a flat file with line numbers; that describes a line-oriented format, not the Junos hierarchy. Option B is incorrect because the Junos configuration is not assembled by merging multiple configuration files at boot; it is maintained as a single hierarchical candidate/active configuration. Option D is incorrect because inheritance in Junos flows from parent levels down to child levels, not automatically from the root level to all statements.

Answer

All configuration is stored in a flat file with line numbers

Answer

The hierarchy is stored in multiple configuration files that are merged at boot

Answer

Configuration values are inherited from the root level automatically

Question 7

Which THREE statements about the Junos OS file system are true? (Choose three.)

Accepted Answer

The active configuration is stored in the /config directory. Option C is correct because the active Junos configuration is saved as juniper.conf.gz in the /config directory, which is a separate partition from the root file system. Option D is correct because Junos OS writes its log files, such as messages and interactive-commands, into the /var/log directory. Option E is correct because the Junos OS file system is a FreeBSD-based, UNIX-like hierarchy containing standard directories including /, /var, and /config. Option A is incorrect because /etc holds system configuration files, not log files, which reside in /var/log. Option B is incorrect because /altroot is a backup root partition used for alternate boot images, not for user-uploaded files, which are typically placed in /var/tmp or /var/home.

Answer

The /etc directory contains all log files

Answer

The /altroot directory is used for user-uploaded files

Question 8

You are a network engineer at a company that operates a pair of Juniper SRX firewalls in an active/passive cluster (Chassis Cluster). The cluster has been running Junos 15.1X49-D100 for over a year. Management has mandated an upgrade to a newer version to address security vulnerabilities. You follow the recommended upgrade procedure and successfully upgrade the primary node (node0) first, then failover to make node0 the backup, and upgrade the new primary (node1). After the upgrade, both nodes have the same version and appear to be in the cluster, but you notice that the backup node (node0) is stuck in 'ineligible' state and does not synchronize configuration changes. What is the most likely cause?

Accepted Answer

The cluster control link is down or misconfigured on the backup node. The backup node being stuck in 'ineligible' state after a chassis cluster upgrade indicates that the cluster control link (control port) is not functioning correctly. In a Juniper SRX active/passive cluster, the control link is used for heartbeat and cluster state synchronization; if it is down or misconfigured on the backup node, the node cannot participate in the cluster election process and remains ineligible. This is a common issue after upgrades if the control link interfaces are not properly re-established or if the cable is faulty.

Answer

The backup node has not been configured with 'commit synchronize'

Answer

The 'set chassis cluster reth-count' statement is missing on the backup node

Answer

The 'monitor interface' configuration is causing a mis-match between nodes

Question 9

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 10

You are a network administrator for a service provider that uses Juniper MX series routers to provide MPLS VPN services to customers. Management has requested that you implement a secure out-of-band management (OOBM) solution for all MX routers to ensure that management traffic is isolated from the production network, reducing the risk of unauthorized access and management plane attacks. You are tasked with designing the OOBM solution using a dedicated management interface (me0) and a separate management routing instance. Which of the following best practices should you follow?

Accepted Answer

Create a dedicated routing instance for management, assign me0 to it, and apply a firewall filter to restrict access. It follows Juniper's best practice for OOBM: creating a dedicated management routing instance (e.g., mgmt_junos) and assigning the me0 interface to it. This ensures management traffic is completely isolated from the production routing table (inet.0), preventing management plane attacks and unauthorized access. Applying a firewall filter on the me0 interface further restricts access to only authorized management hosts, aligning with security hardening guidelines.

Answer

Place me0 in the inet.0 routing table and rely on static routes

Answer

Enable VLAN tagging on me0 to separate management traffic into different subnets

Answer

Configure the me0 interface in the default routing instance with a simple ACL

Question 11

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 12

Which two statements correctly describe Junos OS login classes? (Choose two.)

Accepted Answer

They are defined under the [edit system login class] hierarchy.. Option B is correct because login classes are configured at the [edit system login class class-name] hierarchy in Junos OS, where you define permissions and other login parameters. Option D is correct because a login class can include or exclude the configure permission, thereby restricting whether a user can enter configuration mode. Options A, C, and E are incorrect: login classes do not force operational-mode-only access (that depends on permissions such as configure), they are not automatically assigned to all users by default (each user must be associated with a class, otherwise the default class applies), and they can be modified or deleted after creation.

Answer

They allow users to enter only operational mode.

Answer

They are automatically assigned to all users by default.

Answer

They cannot be modified after creation.

Question 13

A junior network administrator is setting up a Juniper MX router for the first time. After powering on the device, the administrator notices that the LED on the front panel blinks amber and the device does not complete the boot process. The console displays messages reporting file system errors. The administrator has no previous configuration changes and the device was shipped with factory defaults. Which action should the administrator take to resolve the boot issue?

Accepted Answer

Boot into single-user mode and run file system checks.. The amber blinking LED and file system errors indicate a corrupted file system, which is common on factory-default devices if the flash memory was not properly initialized. Booting into single-user mode (option A) allows the administrator to run 'fsck' (file system check) to repair the root file system without loading the full Junos OS, which is the standard recovery procedure for such boot failures.

Answer

Perform a password recovery procedure to gain access.

Answer

Use the 'request system software add' command from the boot loader.

Answer

Reinstall the Junos OS using a USB flash drive with the software image.

Question 14

A network engineer made several configuration changes on a Juniper QFX switch to implement new VLANs. After committing the changes, the engineer realized that the new configuration caused a critical loss of connectivity to the management network. The engineer needs to revert to the previous configuration that was working. The switch is still accessible via the console port, and the engineer has privilege level access. The previous configuration was committed two commits ago, and the current active configuration is the problematic one. Which action should the engineer take to restore the previous working configuration?

Accepted Answer

Execute 'rollback 2' followed by 'commit'.. The working configuration was committed two commits ago. The 'rollback 2' command loads the configuration from two commits prior into the candidate configuration. After that, 'commit' makes it active, restoring connectivity. Note that 'rollback 1' would load the intermediate commit, which is also problematic, and 'rollback 0' refers to the current active configuration.

Answer

Use 'load override /config/juniper.conf.1.gz' followed by 'commit'.

Answer

Use 'delete system' to remove all configuration and then commit.

Answer

Execute 'rollback 0' followed by 'commit'.

Question 15

Which TWO statements are correct regarding the Junos OS configuration hierarchy?

Accepted Answer

The 'show | compare' command displays differences between the candidate and active configurations.. Option C is correct because the 'show | compare' command in Junos displays the differences between the candidate configuration and the active (committed) configuration, allowing operators to review pending changes before committing. Option E is correct because the 'set' command is used in configuration mode to modify the candidate configuration, adding or changing statements in the hierarchy. Option A is incorrect because 'commit check' only validates the candidate configuration for syntax and semantic errors without applying it; the 'commit' command applies it to the active configuration. Option B is incorrect because 'load replace' replaces the entire candidate configuration with the contents of a file, whereas 'load merge' merges a file into the candidate configuration. Option D is incorrect because 'rollback 0' reverts the candidate configuration to the currently active configuration, discarding uncommitted changes; 'rollback 1' reverts to the previous committed configuration.

Answer

The 'commit check' command applies the candidate configuration to the active configuration.

Answer

The 'load replace' command merges a configuration file into the candidate configuration.

Answer

The 'rollback 0' command reverts the candidate configuration to the previous state.