Visit here for our full Juniper JN0-105 exam dumps and practice test questions.
Question 136
What is the purpose of the commit synchronize command in Junos OS?
A) To synchronize time between devices
B) To commit configuration changes on both routing engines simultaneously in a dual RE system
C) To synchronize routing tables
D) To backup configuration to a remote server
Answer: B
Explanation:
To expand on your explanation, it is helpful to delve deeper into the operational mechanics, the configuration options to enforce this behavior, and the interaction with other high-availability features.
The commit synchronize process is not merely a copy-paste operation; it involves a strict sequence of checks to ensure database integrity. When the command is issued, the primary Routing Engine (RE) locks the configuration database on both the local and remote engines. This prevents other administrators from making conflicting changes on the backup RE while the synchronization is in progress. The system then validates the syntax on the local RE. If successful, the candidate configuration is transferred to the backup RE, where a commit check is automatically performed. Only if the configuration is syntactically correct on both engines does the actual activation occur. This atomicity is crucial; it prevents a scenario where a configuration is valid on one engine but invalid on the other due to hardware differences or license mismatches.
Because human error is a significant risk—administrators often forget to append the synchronize keyword—Junos allows you to make this the default behavior. By configuring set system commit synchronize, the router treats every standard commit command as a commit synchronize. This is a best practice in production environments using Graceful Routing Engine Switchover (GRES) and Non-Stop Routing (NSR). Without this automation, a manual failover event could result in the backup RE taking over with a configuration that is weeks or months old, potentially dropping OSPF/BGP neighbors or security policies.
There are nuances when the Routing Engines are not in a perfect steady state. For instance, if the backup RE is down or running a different software version that does not support a specific feature, the standard commit synchronize will fail. In such cases, the force option (e.g., commit synchronize force) can be used to push the configuration despite warnings, though this requires careful validation by the administrator. Furthermore, during a Unified In-Service Software Upgrade (ISSU), this synchronization mechanism is temporarily suspended or managed by the upgrade process to ensure that version-dependent configuration syntax does not cause the system to hang.
Question 137
Which routing table contains IPv4 unicast routes in Junos OS?
A)0
B)0
C)0
D)l3vpn.0
Answer: A
Explanation:
In Junos OS, there is a distinct separation between the Control Plane and the Data Plane. The inet.0 table resides in the Routing Information Base (RIB), which is managed by the Routing Engine (RE). The RIB contains all possible routes learned from all protocols. However, the router cannot forward traffic based on the RIB alone because it is optimized for calculation, not speed.
Once the Routing Protocol Daemon (rpd) selects the best active route from inet.0, it pushes that specific route down to the Forwarding Information Base (FIB) on the Packet Forwarding Engine (PFE). This architecture allows the router to continue forwarding packets at line rate via the hardware PFE even if the Routing Engine is busy processing complex BGP updates or is momentarily unresponsive.
When inet.0 receives multiple routes for the exact same destination prefix (e.g., 192.168.1.0/24) from different protocols, it relies on Route Preference (known as Administrative Distance in Cisco IOS) to break the tie. Lower preference values are preferred.
The default hierarchy ensures reliability:
Directly Connected: Preference 0 (Most trusted)
Static Routes: Preference 5
OSPF Internal: Preference 10
BGP (EBGP): Preference 170
For example, if a router learns the path to a server via both OSPF and EBGP, the route remains in inet.0 for both protocols, but only the OSPF route (Preference 10) is marked as “Active” (denoted by an asterisk * in the CLI) and installed into the FIB.
A critical aspect of troubleshooting inet.0 is understanding that not all learned routes appear in the standard output. If a route is rejected by an import policy, or if the next-hop address is unreachable, the route is marked as hidden.
Standard commands will not show these, which can lead to confusion where a neighbor appears up, but routes are missing.
Command: show route hidden
Purpose: This reveals routes that rpd knows about but refuses to use. This is often the “smoking gun” when debugging route filters or recursive lookup failures.
Question 138
What is the purpose of the request system halt command?
A) To restart the device immediately
B) To gracefully shut down the system before powering off
C) To pause system operations temporarily
D) To stop routing protocols only
Answer: B
Explanation:
The request system halt command in Junos OS is used to gracefully shut down the operating system in preparation for powering off the device. Unlike a simple power-off, this command ensures that all processes terminate cleanly, file systems are synchronized, and any cached data is safely written to storage. This orderly shutdown minimizes the risk of data corruption, file system damage, or other issues that could occur if power were removed abruptly while the system is actively writing data.
When request system halt is executed, Junos initiates a controlled shutdown sequence. The operating system stops running processes, closes open files, synchronizes the file system, and unmounts storage partitions. Once the process completes, the system displays a message indicating that it is safe to remove power. This procedure is essential for maintaining the integrity of the device’s software and configuration, ensuring that the system can boot normally during the next startup.
Administrators should always use request system halt before removing power, especially during hardware maintenance, component replacement, or equipment relocation. Failing to do so can lead to file system inconsistencies, prolonged boot times, or even loss of configuration changes that were in memory but not yet written to storage.
Option A is incorrect because request system reboot restarts the device, whereas request system halt prepares it for a complete power-off. Option C is incorrect because there is no pause or temporary stop functionality; the halt command performs a full shutdown of the system. Option D is incorrect because request system halt affects the entire device, not just routing protocols or individual services.
Question 139
Which command shows the hardware components installed in a Junos device?
A) show hardware
B) show chassis hardware
C) display hardware
D) show system hardware
Answer: B
Explanation:
The show chassis hardware command in Junos OS provides a detailed overview of all physical hardware components installed in a device. This includes the chassis model, serial number, installed line cards, routing engines, power supplies, fan trays, and other field-replaceable units (FRUs). The command presents a comprehensive inventory that is essential for maintenance, troubleshooting, asset management, and upgrade planning.
The output of show chassis hardware is organized hierarchically, with the chassis itself at the top level and sub-components listed beneath. Each component entry typically includes part numbers, serial numbers, version information, and descriptions. In addition, the command often indicates the operational status of each component, allowing administrators to quickly identify failed or missing hardware. This makes it a crucial tool when diagnosing hardware-related issues, verifying component compatibility before upgrades, or ensuring proper documentation for network infrastructure management.
For example, if a fan tray fails, show chassis hardware can confirm its presence, model, and serial number, helping to order the correct replacement. Similarly, before performing a line card upgrade, the command allows verification of installed components to ensure the new hardware is compatible with the existing system. When opening support cases with Juniper Networks, providing the output of show chassis hardware ensures the support team has accurate and complete hardware information.
Option A is incorrect because show hardware without the chassis keyword is not valid syntax in Junos. Option C is incorrect because display hardware is not a valid Junos operational command; the display keyword is only used as a pipe modifier to format output. Option D is incorrect because show system hardware is not the proper Junos command for viewing the hardware inventory of chassis components.
In summary, show chassis hardware is essential for managing physical infrastructure, planning upgrades, troubleshooting hardware issues, and maintaining accurate documentation of Junos devices. Proper use of this command helps ensure devices remain operational and maintainable.
Question 140
What is the function of the commit check command?
A) To commit changes immediately
B) To validate configuration syntax without activating changes
C) To compare configurations
D) To rollback configuration
Answer: B
Explanation:
The commit check command validates the syntax and semantic correctness of the candidate configuration without actually activating the changes or modifying the running configuration. This command allows administrators to verify that their configuration changes are valid before committing them, providing an additional safety check in the configuration process.
When commit check is executed, Junos performs the same validation steps that would occur during a normal commit operation including syntax checking, verifying required statements are present, checking for semantic consistency, and ensuring configuration dependencies are satisfied. If any errors are detected, they are reported with explanations, allowing administrators to correct issues before activation.
The commit check command is particularly useful when making complex configuration changes or when multiple administrators are working on configurations simultaneously. By validating changes before committing, administrators can identify and fix errors without affecting the running configuration or causing service disruptions. This is especially valuable in production environments where configuration errors could have significant impact.
Option A is incorrect because commit check validates without committing; the commit command without check is used to activate changes. Option C is wrong as show compare is used to compare configurations, not commit check. Option D is incorrect because rollback commands are used to revert configurations, not commit check which validates proposed changes.
Understanding commit check helps administrators maintain configuration quality and prevent errors from being activated on production devices.
Question 141
Which Junos feature provides automatic failover between redundant routing engines?
A) Graceful Routing Engine Switchover (GRES)
B) Virtual Router Redundancy Protocol (VRRP)
C) Link Aggregation
D) Bidirectional Forwarding Detection (BFD)
Answer: A
Explanation:
Graceful Routing Engine Switchover (GRES) is a Junos high-availability feature that enables automatic failover from a primary routing engine to a backup routing engine without disrupting traffic forwarding or requiring routing protocol adjacencies to be re-established. GRES maintains kernel state synchronization between routing engines so that forwarding continues seamlessly during switchover events.
GRES works by continuously synchronizing critical kernel information from the primary routing engine to the backup routing engine, including forwarding table entries, interface states, and other essential data structures. When a failure occurs on the primary routing engine, the backup immediately assumes control using the synchronized state information, allowing packet forwarding to continue without interruption.
For complete high availability, GRES is typically deployed with Nonstop Active Routing (NSR) which maintains routing protocol state across switchovers, or with helper protocols like BFD or graceful restart capabilities in routing protocols. The combination of these features provides comprehensive protection against routing engine failures with minimal impact on network operations.
Option B is incorrect because VRRP provides gateway redundancy between separate devices, not routing engine redundancy within a single chassis. Option C is wrong as link aggregation provides redundancy for network connections, not routing engine failover. Option D is incorrect because BFD detects failures quickly but does not provide routing engine redundancy; it complements GRES by enabling rapid failure detection.
Understanding GRES capabilities is important for designing and managing high-availability network infrastructures with Junos devices.
Question 142
What is the purpose of the load merge command in Junos configuration mode?
A) To delete the current configuration
B) To merge new configuration statements with existing configuration
C) To replace the entire configuration
D) To validate configuration files
Answer: B
Explanation:
The load merge command in Junos configuration mode merges new configuration statements from a file with the existing candidate configuration, adding new statements while preserving existing configuration that is not explicitly replaced or deleted. This command is useful for applying configuration changes from templates or scripts without removing unrelated existing configuration.
When load merge is executed with a filename, Junos reads the configuration statements from the specified file and integrates them into the candidate configuration. If the file contains configuration for elements that already exist, those elements are updated with the new values. Configuration elements not mentioned in the loaded file remain unchanged, making merge operations safer than replace operations for partial configuration updates.
The load merge command is commonly used in automation scenarios where configuration templates are applied to devices, when restoring partial configurations from backups, or when applying standardized configuration snippets across multiple devices. After loading configuration with merge, administrators can review changes using show compare before committing.
Option A is incorrect because load merge adds to existing configuration rather than deleting it; the load replace command would replace configuration. Option C is wrong as load override replaces entire configuration, not load merge which integrates changes. Option D is incorrect because validation occurs during commit operations, not specifically through load commands, though load commands do perform basic syntax checking.
Understanding load merge helps administrators apply configuration changes efficiently without risking unintended removal of existing configuration.
Question 143
Which command displays real-time interface traffic statistics in Junos OS?
A) show interfaces extensive
B) monitor interface traffic
C) show interface statistics
D) watch interface
Answer: B
Explanation:
The monitor interface traffic command displays real-time, continuously updating interface traffic statistics in Junos OS, providing a dynamic view of packet and byte counters that refresh automatically. This command is invaluable for observing traffic patterns, verifying that traffic is flowing as expected, and troubleshooting connectivity or performance issues.
When monitor interface traffic is executed, Junos displays a screen that continuously updates with current traffic statistics including input and output packet rates, byte rates, and error counters for all interfaces or for specific interfaces if specified. The display updates every second by default, showing administrators immediate feedback about traffic conditions without requiring repeated command execution.
The monitoring display can be filtered to show specific interfaces using syntax like monitor interface traffic ge-0/0/0, or can include additional detail with options. Administrators can exit the monitor mode by pressing Ctrl+C or ‘q’ to return to the normal command prompt. This real-time monitoring capability complements static snapshots provided by show commands.
Option A is incorrect because show interfaces extensive provides detailed statistics but is a static snapshot, not real-time monitoring. Option C is wrong as show interface statistics is not valid Junos syntax for viewing statistics. Option D is incorrect because watch is not a Junos command; monitor is used for real-time displays.
Understanding real-time monitoring commands helps administrators observe network behavior dynamically and respond quickly to traffic anomalies.
Question 144
What is the default behavior of Junos OS when multiple static routes exist to the same destination?
A) Load balancing across all routes
B) Only the route with the lowest metric is installed
C) All routes are installed and load balanced by default
D) Routes are ignored
Answer: B
Explanation:
When multiple static routes exist to the same destination prefix in Junos OS, only the route with the lowest metric value is installed into the forwarding table by default. If multiple static routes have equal metrics, Junos can install multiple routes for load balancing, but this requires equal-cost multipath (ECMP) to be enabled or implicitly supported.
Junos evaluates routes based on preference first (static routes have a default preference of 5), then by metric when preferences are equal. The metric for static routes defaults to a value that varies based on next-hop type, but can be explicitly configured using the metric option in the static route statement. Lower metric values are preferred over higher values.
To enable load balancing across multiple equal-cost static routes, administrators can configure multiple static routes with the same destination and equal metrics. Junos will then install multiple next-hops in the forwarding table and distribute traffic across them. The specific load-balancing behavior can be controlled through routing policies and forwarding options.
Option A is incorrect because automatic load balancing requires routes to have equal metrics; it is not the default for routes with different metrics. Option C is wrong as not all routes are automatically installed and load balanced; metric comparison determines which routes are active. Option D is incorrect because routes are not ignored; Junos follows standard route selection algorithms.
Understanding route selection behavior helps administrators configure routing correctly and predict which paths traffic will follow.
Question 145
Which Junos command displays the ARP table?
A) show arp
B) show ip arp
C) display arp
D) get arp
Answer: A
Explanation:
The show arp command displays the Address Resolution Protocol (ARP) table in Junos OS, showing the mapping between IPv4 addresses and MAC addresses for devices on directly connected networks. The ARP table is essential for Layer 2 to Layer 3 address resolution and is used by the device to determine destination MAC addresses when forwarding packets on local networks.
The show arp output includes columns for IP addresses, MAC addresses, interface names, and flags indicating the type of ARP entry such as permanent or dynamic. The command can be filtered to show ARP entries for specific interfaces using syntax like show arp interface ge-0/0/0, or to search for specific IP addresses. This information is crucial for troubleshooting connectivity issues at Layer 2.
ARP entries are typically learned dynamically as the device communicates with other hosts, but static ARP entries can also be configured. The show arp command displays both types, helping administrators verify that address resolution is working correctly and identify any conflicts or issues with MAC address learning.
Option B is incorrect because show ip arp is Cisco IOS syntax, not Junos; Junos uses simply show arp. Option C is wrong as display arp is not valid Junos syntax; display is used as a pipe modifier. Option D is incorrect because get arp is not proper Junos command syntax.
Understanding how to view the ARP table is fundamental for troubleshooting Layer 2 connectivity and verifying proper address resolution.
Question 146
What is the purpose of the set cli screen-length command?
A) To change the terminal width
B) To set the number of lines displayed before pausing output
C) To adjust font size
D) To configure screen resolution
Answer: B
Explanation:
The set cli screen-length command configures the number of lines that Junos displays before pausing output and presenting a “more” prompt, allowing administrators to control how much information appears on screen at once. This setting helps manage output from commands that produce lengthy results, making it easier to review information without overwhelming the terminal display.
By default, Junos pauses output after displaying a screen full of information, allowing administrators to press space to see the next page, enter to advance one line, or ‘q’ to quit the display. The screen-length setting can be customized to match the administrator’s terminal size or preferences, with values typically ranging from 0 (no pagination) to large numbers for terminals with many visible lines.
Setting screen-length to 0 disables pagination entirely, causing all output to display without pausing. This is useful when capturing output to files or when working with terminal programs that have their own scrollback capabilities. Administrators can set this value per session using set cli screen-length or make it persistent in their user configuration.
Option A is incorrect because terminal width is configured with set cli screen-width, not screen-length which controls vertical display. Option C is wrong as font size is a function of the terminal emulator, not Junos configuration. Option D is incorrect because screen resolution is controlled by the terminal program or operating system, not Junos CLI settings.
Understanding CLI display options helps administrators work more efficiently with command output in various terminal environments.
Question 147
Which file contains the Junos OS configuration that becomes active after a reboot?
A) /config/juniper.conf
B) /var/tmp/config.txt
C) /config/juniper.conf.gz
D) /etc/config/running.conf
Answer: C
Explanation:
The file /config/juniper.conf.gz contains the active Junos OS configuration that is loaded when the device boots. This compressed configuration file stores the last successfully committed configuration and persists across reboots, ensuring that the device maintains its configuration even after power cycles or system restarts.
When administrators commit configuration changes in Junos, the new configuration is written to /config/juniper.conf.gz after successful validation. During the boot process, Junos reads this file, decompresses it, and loads the configuration as the active running configuration. This automatic loading ensures configuration persistence without requiring manual intervention.
The .gz extension indicates that the file is compressed using gzip compression to save storage space. Administrators can view the contents using commands like show configuration or by manually decompressing the file if needed for troubleshooting. Junos also maintains backup configuration files in the /config directory for rollback purposes.
Option A is incorrect because the configuration file is compressed and stored as juniper.conf.gz, not juniper.conf without compression. Option B is wrong as /var/tmp is for temporary files and does not contain the persistent boot configuration. Option D is incorrect because /etc/config/running.conf is not the Junos configuration file location; Junos uses /config/juniper.conf.gz.
Understanding configuration file locations is important for backup procedures, disaster recovery planning, and advanced troubleshooting scenarios.
Question 148
What is the function of the request support information command?
A) To request technical support from Juniper
B) To collect comprehensive system information for troubleshooting
C) To display support contract details
D) To update support software
Answer: B
Explanation:
The request support information command collects comprehensive diagnostic and configuration information from the Junos device and saves it to a file that can be provided to Juniper Networks technical support or used for internal troubleshooting. This command gathers logs, configuration files, system information, and diagnostic output into a single compressed archive.
The collected information includes the active configuration, system logs, routing table information, interface statistics, protocol state information, hardware inventory, and various diagnostic outputs. This comprehensive data collection helps support engineers or administrators analyze issues without needing direct access to the device or requiring multiple separate command executions.
The output file is typically saved in /var/tmp with a filename indicating the hostname and timestamp. Administrators can then transfer this file to support personnel using SCP, FTP, or other file transfer methods. The file name format is typically hostname_timestamp.tgz, making it easy to identify which device and time period the information represents.
Option A is incorrect because the command collects information rather than requesting support; contacting support is a separate process. Option C is wrong as contract details are viewed through the Juniper support portal, not this command. Option D is incorrect because software updates are performed using request system software commands, not request support information.
Understanding information collection capabilities helps administrators provide comprehensive diagnostic data efficiently when troubleshooting issues.
Question 149
Which routing protocol preference value is lowest (most preferred) in Junos OS by default?
A) Static routes (5)
B) OSPF internal routes (10)
C) Direct routes (0)
D) BGP routes (170)
Answer: C
Explanation:
Direct routes have the lowest preference value of 0 in Junos OS, making them the most preferred routes by default. Direct routes are automatically created for networks that are directly connected to the device’s interfaces when those interfaces are configured with IP addresses and brought into an operational state.
The preference value (similar to administrative distance in other operating systems) determines which route source is preferred when multiple routing protocols provide routes to the same destination. Lower preference values are more trusted, with direct routes having the highest trust because they represent networks that are physically connected to the device.
The default preference hierarchy in Junos includes direct routes at 0, static routes at 5, OSPF internal routes at 10, IS-IS Level 1 internal at 15, IS-IS Level 2 internal at 18, OSPF external at 150, and BGP at 170. Administrators can modify these preferences using routing policies when specific route selection behavior is needed for particular network designs.
Option A is incorrect because static routes have preference 5, which is higher (less preferred) than direct routes. Option B is wrong as OSPF internal routes have preference 10, also less preferred than direct routes. Option D is incorrect because BGP routes have preference 170, much less preferred than direct routes.
Understanding preference values is crucial for predicting which routes Junos will select when multiple sources provide routing information for the same destinations.
Question 150
What is the purpose of the archive configuration statement in Junos OS?
A) To compress log files
B) To automatically backup configuration changes to specified locations
C) To delete old configurations
D) To encrypt configuration files
Answer: B
Explanation:
The archive configuration statement in Junos OS enables automatic backup of configuration changes to specified locations such as remote servers via FTP, SCP, or HTTP, or to local file system locations. This feature ensures that configuration history is preserved externally, providing protection against device failure and maintaining an audit trail of configuration changes.
When archive configuration is configured, Junos automatically transfers a copy of the configuration to the specified location after each successful commit operation. Administrators can configure multiple archive destinations, set the number of archived configurations to retain, and specify whether to archive only when configurations change or on every commit.
The archive feature can be configured with transfer-on-commit to upload immediately after commits, or transfer-interval to upload periodically. Authentication credentials for remote servers can be configured, and administrators can specify filename formats that include timestamps or version numbers for easy identification and organization of archived configurations.
Option A is incorrect because log file compression is handled separately from configuration archiving. Option C is wrong as archive preserves configurations rather than deleting them, though retention policies can be configured. Option D is incorrect because encryption is configured separately if needed; archive focuses on backing up configurations to external locations.
Understanding configuration archiving helps organizations maintain proper backup procedures and meet compliance requirements for configuration change tracking.