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Question 75: 

What is the primary purpose of the Junos CLI operational mode?

A) To configure the device

B) To monitor device status and execute troubleshooting commands

C) To install software updates

D) To manage user accounts

Answer: B

Explanation:

The Junos CLI operational mode is designed primarily for monitoring device status, viewing operational information, and executing troubleshooting commands without making configuration changes to the device. This mode is the default mode users enter when they first log into a Junos device and provides a safe environment for viewing system information and running diagnostic commands without risk of accidentally modifying the device configuration.

In operational mode, administrators can execute commands to view routing tables, interface statistics, system logs, protocol status, and various other operational metrics. Common operational mode commands include show route to display routing information, show interfaces to view interface status and statistics, show log to examine system logs, and ping or traceroute for network connectivity testing. These commands provide essential visibility into device operation and are critical for monitoring network health and troubleshooting issues when they arise.

The operational mode prompt is indicated by a greater-than sign (>) followed by the username or hostname. From operational mode, users can enter configuration mode by typing configure, but operational mode itself does not allow configuration changes. This separation between operational and configuration modes is a key security and operational feature of Junos OS, ensuring that viewing system information and testing connectivity does not inadvertently result in configuration modifications. The operational mode also provides access to various shell commands and system utilities through the start shell command for advanced troubleshooting and system administration tasks.

Option A is incorrect because device configuration is performed in configuration mode, not operational mode. Users must explicitly enter configuration mode by typing configure to make configuration changes.

Option C is incorrect because while software installation commands can be initiated from operational mode using request system software commands, this is not the primary purpose of operational mode, which focuses on monitoring and troubleshooting.

Option D is incorrect because managing user accounts involves configuration changes that must be done in configuration mode, not operational mode. Operational mode is for viewing information rather than making system changes.

Question 76: 

Which command is used to enter configuration mode in Junos OS?

A) config

B) configure

C) edit

D) set config

Answer: B

Explanation:

The configure command is used to enter configuration mode from operational mode in Junos OS. This command transitions the CLI from the operational mode where monitoring and troubleshooting commands are executed to configuration mode where administrators can make changes to the device configuration. Configuration mode is essential for modifying system settings, configuring interfaces, setting up routing protocols, defining security policies, and making any other configuration changes to the Junos device.

When the configure command is executed, the CLI prompt changes from the operational mode prompt (indicated by >) to the configuration mode prompt (indicated by #), providing a clear visual indication of the current mode. In configuration mode, administrators can use various commands including set to add configuration statements, delete to remove configuration, edit to navigate into specific configuration hierarchies, and show to display current configuration settings. Configuration mode also supports features like configuration validation, commit checks, and the ability to review changes before applying them.

Junos OS provides several variations of the configure command for different scenarios. The standard configure command enters configuration mode in exclusive mode on devices that support it, preventing other users from making simultaneous configuration changes. The configure private command creates a private candidate configuration that does not interfere with other users’ configurations. These options provide flexibility for different operational scenarios while maintaining configuration integrity and preventing conflicting changes from multiple administrators.

Option A is incorrect because config is not a valid command in Junos OS for entering configuration mode. The full command configure must be used, although some CLI shortcuts may work depending on context.

Option C is incorrect because edit is used within configuration mode to navigate into specific configuration hierarchies, not to enter configuration mode from operational mode. The edit command changes the current hierarchy level within configuration mode.

Option D is incorrect because set config is not a valid command syntax in Junos OS. The set command is used within configuration mode to add configuration statements, but entering configuration mode requires the configure command.

Question 77: 

What does the commit command do in Junos configuration mode?

A) Saves changes to a backup file

B) Activates and applies configuration changes to the running system

C) Displays pending changes

D) Exits configuration mode

Answer: B

Explanation:

The commit command in Junos configuration mode activates and applies all pending configuration changes to the running system, making them effective immediately. This command is a critical part of the Junos configuration workflow and represents the final step in applying configuration changes after they have been entered and validated. Unlike some network operating systems that apply changes immediately as they are entered, Junos uses a candidate configuration approach where changes are staged first and only become active when explicitly committed.

When the commit command is executed, Junos performs several important operations. First, it validates the candidate configuration to ensure there are no syntax errors, missing required statements, or logical inconsistencies. If validation passes, the system activates the new configuration by copying the candidate configuration to become the active configuration. The previous active configuration is automatically saved as a rollback configuration, allowing administrators to revert changes if problems occur. This commit process provides a safety mechanism that prevents invalid configurations from being activated and allows for easy recovery if issues arise.

Junos supports several commit command variations for different scenarios. The commit check command validates the configuration without actually activating it, allowing administrators to verify changes will work before applying them. The commit confirmed command requires a second commit within a specified time period or the configuration automatically rolls back, providing protection against configuration changes that might lock administrators out of the device. The commit and-quit command commits changes and exits configuration mode in a single operation, streamlining the workflow for simple configuration tasks.

Option A is incorrect because the commit command does not save changes to a backup file. It activates configuration changes and makes them the running configuration. Backup configurations are created automatically as rollback files during the commit process.

Option C is incorrect because displaying pending changes is done with the show command or show | compare command in configuration mode, not the commit command. The commit command applies changes rather than displaying them.

Option D is incorrect because the commit command does not exit configuration mode. After committing, the administrator remains in configuration mode. To exit, the quit or exit command must be used separately after the commit.

Question 78: 

Which Junos configuration hierarchy contains interface settings?

A) [edit system]

B) [edit interfaces]

C) [edit protocols]

D) [edit routing-options]

Answer: B

Explanation:

The [edit interfaces] hierarchy in Junos configuration contains all interface-related settings including physical interface properties, logical unit configurations, IP addressing, VLAN tagging, interface descriptions, and various interface-specific parameters. This hierarchy is fundamental to device configuration as interfaces are the primary connection points for network traffic and must be properly configured for the device to function in the network.

Within the [edit interfaces] hierarchy, configuration is organized by interface name and logical unit number. Physical interfaces are identified by their interface type and slot/port location such as ge-0/0/0 for Gigabit Ethernet or xe-0/0/0 for 10 Gigabit Ethernet. Under each physical interface, administrators configure logical units using the unit statement, with unit 0 being the most common for simple configurations. Each unit can have its own family configuration (such as inet for IPv4 or inet6 for IPv6) with associated IP addresses, and additional parameters like MTU, bandwidth, and various protocol-specific settings.

The interfaces hierarchy supports a wide range of configuration options depending on interface type and purpose. Common configurations include setting interface descriptions for documentation, configuring speed and duplex settings, enabling or disabling interfaces, setting up VLAN tagging, configuring link aggregation, and defining various layer 2 and layer 3 parameters. The hierarchical structure makes it easy to organize and manage interface configurations, with clear separation between physical interface properties and logical unit configurations. Understanding the interfaces hierarchy is essential for any Junos administrator as interface configuration is one of the most common tasks in network device management.

Option A is incorrect because the [edit system] hierarchy contains system-wide settings such as hostname, DNS servers, NTP configuration, user accounts, and system services, not interface-specific settings.

Option C is incorrect because the [edit protocols] hierarchy contains routing protocol configurations such as OSPF, BGP, and IS-IS settings, not interface configuration. While protocols may reference interfaces, the interface definitions themselves are in the interfaces hierarchy.

Option D is incorrect because the [edit routing-options] hierarchy contains routing-related settings such as static routes, route preferences, and routing table options, not interface configuration parameters.

Question 79: 

What is the purpose of the rollback command in Junos?

A) To restart the device

B) To revert to a previous configuration

C) To delete all configurations

D) To upgrade software

Answer: B

Explanation:

The rollback command in Junos is used to revert the candidate configuration to a previous configuration state, providing a powerful mechanism for recovering from configuration errors or undoing unwanted changes. Junos automatically maintains multiple previous configurations as numbered rollback files, allowing administrators to quickly return to known good configurations without manually recreating settings or restoring from external backups.

When configurations are committed, Junos automatically saves the previous active configuration as a rollback file. By default, Junos maintains the last 50 committed configurations numbered from 0 to 49, where rollback 0 is the currently active configuration, rollback 1 is the previous configuration, rollback 2 is the one before that, and so on. Administrators can use the rollback command followed by a number to load any of these saved configurations into the candidate configuration. For example, rollback 1 loads the previous configuration, allowing administrators to review it and commit if desired to restore the previous state.

The rollback feature is invaluable for troubleshooting and recovery scenarios. If a configuration change causes problems, administrators can quickly rollback to the previous working configuration and commit it to restore normal operation. The rollback command can be used multiple times before committing, and administrators can compare different rollback configurations using show | compare rollback commands to see exactly what changed between configuration versions. This capability significantly reduces the risk associated with configuration changes and provides confidence that problems can be quickly resolved by reverting to earlier configurations.

Option A is incorrect because restarting the device is done with the request system reboot command in operational mode, not the rollback command. Rollback affects configuration state, not system operation.

Option C is incorrect because rollback does not delete all configurations. It loads a previous configuration into the candidate configuration, and even then only affects the configuration when committed. To delete configuration, specific delete commands would be used.

Option D is incorrect because software upgrades are performed using request system software commands in operational mode, not the rollback command. Rollback specifically deals with configuration management, not software installation.

Question 80: 

Which command displays the candidate configuration in Junos configuration mode?

A) display config

B) show configuration

C) show

D) list config

Answer: C

Explanation:

The show command in Junos configuration mode displays the candidate configuration or portions of it depending on the current hierarchy level and any additional parameters specified. This command is essential for reviewing configuration settings, verifying changes before committing, and understanding the current configuration state. The show command can be used at any hierarchy level within configuration mode to display relevant configuration statements.

When used without additional parameters at the top level of configuration mode, the show command displays the entire candidate configuration. When used within a specific configuration hierarchy such as [edit interfaces], the show command displays only the configuration statements relevant to that hierarchy level. Administrators can also use show with specific hierarchy paths to view configuration from other parts of the hierarchy without navigating to those locations. For example, show interfaces displays all interface configuration regardless of the current hierarchy position.

The show command supports various options and pipe modifiers that provide powerful filtering and formatting capabilities. The show | compare command displays differences between the candidate configuration and the active configuration, highlighting what changes have been made during the current configuration session. The show | display set command shows configuration in set command format, which is useful for copying configuration or understanding the exact commands needed to recreate configuration statements. Other display options include show | display xml for XML format and show | match or show | except for filtering output based on patterns. These capabilities make the show command an indispensable tool for configuration management and verification.

Option A is incorrect because display config is not a valid command in Junos. The correct command is show, which can use display options through pipe modifiers like show | display set.

Option B is incorrect because while show configuration might seem logical, the actual command in configuration mode is simply show. The word configuration is not required as the context of being in configuration mode makes it clear.

Option D is incorrect because list config is not a valid Junos command. The show command is used to display configuration, and list is not a standard Junos CLI command for viewing configuration.

Question 81: 

What is the function of the set command in Junos configuration mode?

A) To display configuration

B) To add or modify configuration statements

C) To delete configuration

D) To exit configuration mode

Answer: B

Explanation:

The set command in Junos configuration mode is used to add new configuration statements or modify existing configuration settings within the candidate configuration. This command is one of the primary methods for building and changing device configuration in Junos, allowing administrators to specify exactly what configuration elements should be added or changed using a clear and explicit syntax.

The set command follows a hierarchical syntax that mirrors the Junos configuration structure. A complete set command includes the full hierarchy path followed by the configuration statement and any associated values. For example, set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24 adds an IP address to an interface by specifying the complete path through the interfaces hierarchy to the specific setting. This explicit syntax makes set commands self-documenting and easy to understand, as each command clearly shows exactly what is being configured and where in the configuration hierarchy it belongs.

The set command is idempotent, meaning it can be executed multiple times with the same parameters without creating duplicate entries or causing errors. If a set command specifies a configuration statement that already exists with the same value, the command has no effect. If the statement exists with a different value, the set command updates it to the new value. This behavior makes set commands safe to use in scripts and automation tools, as they can be executed repeatedly without concern about the current configuration state. The set command format is also commonly used when displaying configuration with the show | display set command, making it easy to copy configuration or create configuration templates.

Option A is incorrect because displaying configuration is done with the show command, not the set command. The set command is for adding or modifying configuration, not viewing it.

Option C is incorrect because deleting configuration is done with the delete command in configuration mode, not the set command. While set can modify values, it does not remove configuration statements.

Option D is incorrect because exiting configuration mode is done with the exit or quit command, not the set command. The set command operates within configuration mode to make configuration changes.

Question 82: 

Which command deletes configuration statements in Junos?

A) remove

B) delete

C) clear

D) erase

Answer: B

Explanation:

The delete command in Junos configuration mode removes configuration statements from the candidate configuration. This command allows administrators to remove unwanted or incorrect configuration elements, and its syntax mirrors the set command syntax for consistency and ease of use. The delete command is essential for maintaining clean configurations and removing deprecated or unnecessary settings.

The delete command uses the same hierarchical syntax as the set command, specifying the full path to the configuration element that should be removed. For example, delete interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24 removes a specific IP address from an interface. Administrators can delete at various levels of the hierarchy depending on how much configuration should be removed. Deleting at a higher level removes all configuration under that hierarchy, so delete interfaces ge-0/0/0 would remove all configuration for that interface including all units and settings.

The delete command provides flexibility in configuration management. Administrators can delete specific leaf statements like individual IP addresses or routing protocol parameters, or they can delete entire configuration containers to remove branches of the configuration hierarchy. When using delete, it is important to understand the scope of what is being removed, as deleting a container removes everything beneath it in the hierarchy. The show | compare command is useful after using delete to review what configuration will be removed when the changes are committed, helping prevent accidental deletion of important configuration elements.

Option A is incorrect because remove is not a valid Junos configuration command for deleting configuration statements. The correct command is delete, which follows the standard Junos configuration syntax.

Option C is incorrect because clear is not used for deleting configuration in Junos. While clear might be used in operational mode for certain tasks like clearing statistics, configuration deletion requires the delete command.

Option D is incorrect because erase is not a Junos configuration command. The delete command is the standard and correct method for removing configuration statements from the candidate configuration.

Question 83: 

What does the pipe symbol (|) do when used with show commands in Junos?

A) Creates a backup

B) Filters or modifies command output

C) Commits configuration

D) Exits the CLI

Answer: B

Explanation:

The pipe symbol (|) in Junos is used with show commands to filter, modify, or format the command output, providing powerful text processing capabilities that help administrators quickly find relevant information in potentially lengthy output. The pipe symbol redirects command output through various filters and modifiers that can match patterns, exclude patterns, display specific formats, count lines, or perform other text processing operations.

Common pipe modifiers include match and except for pattern-based filtering. The match modifier displays only lines containing a specified pattern, making it easy to find specific information in large outputs. For example, show configuration | match ospf displays only configuration lines containing the word ospf. The except modifier does the inverse, showing all lines except those matching the pattern. Other useful modifiers include display set to show configuration in set command format, display xml for XML output, display json for JSON format, and count to display the number of lines in the output.

The pipe functionality in Junos is similar to Unix/Linux pipe operations and provides powerful capabilities for command-line data processing. Multiple pipe modifiers can be chained together to perform complex filtering and formatting operations. For example, show route | match “172.16” | except inactive shows only routes containing 172.16 but excludes any lines with the word inactive. Understanding and using pipe modifiers effectively is a key skill for Junos administrators as it enables efficient navigation and analysis of device information without requiring external tools or manual searching through large amounts of output.

Option A is incorrect because creating backups is not the function of the pipe symbol. Backups are created automatically during commit operations or manually using specific backup commands, not through pipe operations.

Option C is incorrect because committing configuration is done with the commit command, not with the pipe symbol. The pipe symbol only affects how command output is displayed or filtered.

Option D is incorrect because exiting the CLI is done with the exit or quit commands, not with the pipe symbol. The pipe symbol modifies command output but does not affect CLI session state.

Question 84: 

Which Junos configuration hierarchy contains routing protocol configurations?

A) [edit routing-options]

B) [edit protocols]

C) [edit interfaces]

D) [edit system]

Answer: B

Explanation:

The [edit protocols] hierarchy in Junos contains configurations for routing protocols such as OSPF, BGP, IS-IS, RIP, and other dynamic routing protocols. This hierarchy is where administrators configure protocol-specific parameters including protocol enablement, neighbor relationships, authentication, route policies, timers, and various other protocol behaviors. Understanding the protocols hierarchy is essential for configuring routing in Junos networks.

Within the [edit protocols] hierarchy, each routing protocol has its own sub-hierarchy with protocol-specific configuration options. For example, [edit protocols ospf] contains OSPF configuration including area definitions, interface assignments, and OSPF-specific parameters. Similarly, [edit protocols bgp] contains BGP configuration including autonomous system numbers, peer group definitions, neighbor configurations, and BGP policy settings. Each protocol hierarchy is structured to reflect the logical organization of that protocol’s configuration requirements.

The protocols hierarchy works in conjunction with other configuration hierarchies to provide complete routing functionality. Interface configurations in [edit interfaces] define the physical and logical interfaces that protocols will use. Routing policy configurations that may be referenced in the protocols hierarchy are defined in [edit policy-options]. Global routing settings such as router ID and static routes are configured in [edit routing-options]. This separation of concerns across different hierarchies provides a clean and organized configuration structure that makes complex routing configurations manageable and maintainable.

Option A is incorrect because [edit routing-options] contains global routing settings like static routes, router ID, and routing table options, not dynamic routing protocol configurations. While related to routing, it is separate from protocol configurations.

Option C is incorrect because [edit interfaces] contains interface configuration including IP addresses and interface parameters, not routing protocol configurations. Interfaces are referenced by protocols but the protocol configurations themselves are in the protocols hierarchy.

Option D is incorrect because [edit system] contains system-wide settings like hostname, services, and user accounts, not routing protocol configurations. System settings are separate from routing protocol configurations.

Question 85: 

What is the purpose of the commit check command in Junos?

A) To activate configuration changes

B) To validate configuration syntax without activating changes

C) To display current configuration

D) To create a backup

Answer: B

Explanation:

The commit check command in Junos validates the candidate configuration syntax and logical consistency without actually activating the changes or making them the running configuration. This command is extremely useful for administrators who want to verify that their configuration changes are valid before applying them to the live system, providing a safety mechanism that helps prevent configuration errors from affecting device operation.

When commit check is executed, Junos performs the same validation checks that would occur during a normal commit operation, including syntax verification, checking for required statements, validating references between configuration elements, and ensuring logical consistency of the configuration. If validation fails, commit check displays error messages describing the problems, allowing administrators to correct issues before attempting an actual commit. If validation succeeds, commit check reports success but does not activate the configuration, leaving the candidate configuration unchanged and the active configuration unaffected.

The commit check command is particularly valuable in several scenarios. During initial configuration or major changes, administrators can verify their configuration will work before activating it. When learning Junos or testing new configurations, commit check provides feedback on configuration correctness without risk of disrupting device operation. In change control processes, commit check can be used as a validation step before scheduling actual configuration activation. Many administrators make it a standard practice to always run commit check before commit, especially for complex or critical configuration changes, as it provides an additional verification step that can catch errors before they affect network operation.

Option A is incorrect because activating configuration changes is done with the commit command, not commit check. The commit check command only validates without activating, providing a test mechanism without making changes live.

Option C is incorrect because displaying current configuration is done with the show command, not commit check. The commit check command validates configuration rather than displaying it.

Option D is incorrect because creating backups happens automatically during normal commit operations, not through the commit check command. Commit check only validates configuration without creating backups or changing any files.

Question 86: 

Which command navigates into a specific configuration hierarchy level in Junos?

A) enter

B) edit

C) cd

D) move

Answer: B

Explanation:

The edit command in Junos configuration mode is used to navigate into a specific configuration hierarchy level, changing the current working location within the configuration tree. This command allows administrators to move deeper into the configuration hierarchy, making it easier to work with configuration elements within a specific context without needing to specify the full hierarchy path for every subsequent command.

When the edit command is used with a hierarchy path, the CLI prompt changes to reflect the current location in the configuration hierarchy. For example, from the top level of configuration mode shown as [edit], executing edit interfaces ge-0/0/0 changes the prompt to [edit interfaces ge-0/0/0], indicating the current working location. All subsequent commands are executed relative to this location, so set unit 0 family inet address 192.168.1.1/24 would add the address to ge-0/0/0 without needing to specify the full path.

The edit command is particularly useful when making multiple changes within the same hierarchy level. Instead of typing the full path for each set or delete command, administrators can navigate to the relevant hierarchy location once and then use shorter relative commands. To move back up the hierarchy, the up command moves up one level, or exit can be used to return to the top level. The edit command can also create new hierarchy levels that do not yet exist, making it useful for building new configuration sections. Understanding how to effectively use edit to navigate the configuration hierarchy is an important skill for efficient Junos configuration management.

Option A is incorrect because enter is not a valid Junos command for navigating configuration hierarchies. The correct command is edit, which changes the current hierarchy level in configuration mode.

Option C is incorrect because while cd is used in Unix/Linux file systems for directory navigation, it is not the standard command in Junos configuration mode. The edit command serves the hierarchy navigation function in Junos.

Option D is incorrect because move is not a Junos command for hierarchy navigation. The edit command is the correct tool for changing the current configuration hierarchy level.

Question 87: 

What does the up command do in Junos configuration mode?

A) Increases interface bandwidth

B) Moves up one level in the configuration hierarchy

C) Enables an interface

D) Upgrades software

Answer: B

Explanation:

The up command in Junos configuration mode moves the current hierarchy position up one level toward the root of the configuration tree. This command is used for navigating the configuration hierarchy, allowing administrators to move back to parent levels after using the edit command to navigate into deeper hierarchy levels. Understanding hierarchy navigation commands like up is essential for efficient configuration management in Junos.

When working in a specific configuration hierarchy such as [edit interfaces ge-0/0/0 unit 0], executing the up command changes the current position to the parent level [edit interfaces ge-0/0/0]. Executing up again moves to [edit interfaces], and another up command returns to the top level [edit]. The CLI prompt always displays the current hierarchy location in square brackets, making it easy to track your position in the configuration tree. This navigation capability allows administrators to work efficiently within nested configuration structures without constantly specifying full hierarchy paths.

The up command is particularly useful when making configuration changes across multiple related hierarchy levels or when exploring configuration structure. Combined with the edit command for moving down into the hierarchy and top or exit for returning to the top level, administrators have complete control over their position in the configuration tree. This navigation model mirrors file system directory navigation in Unix/Linux systems, making it intuitive for administrators familiar with those environments. Efficient use of hierarchy navigation commands significantly speeds up configuration tasks and makes working with complex configurations more manageable.

Option A is incorrect because increasing interface bandwidth is a configuration setting that would be done with set commands specifying bandwidth parameters, not with the up command. The up command is for hierarchy navigation only.

Option C is incorrect because enabling an interface involves removing the disable statement or not configuring disable in the first place, not using the up command. Interface state management is separate from hierarchy navigation.

Option D is incorrect because software upgrades are performed using request system software commands in operational mode, not the up command in configuration mode. The up command solely navigates configuration hierarchy levels.

Question 88: 

Which command displays differences between the candidate and active configurations?

A) show changes

B) show diff

C) show | compare

D) compare config

Answer: C

Explanation:

The show | compare command in Junos configuration mode displays the differences between the candidate configuration (the configuration currently being edited) and the active configuration (the currently running configuration on the device). This command is essential for reviewing what changes have been made during a configuration session before committing them, helping administrators verify that only intended changes will be activated and preventing accidental modifications.

When executed, show | compare displays output in a format similar to Unix diff, using plus signs (+) to indicate lines that will be added and minus signs (-) to indicate lines that will be removed when the candidate configuration is committed. This clear visual representation makes it easy to understand exactly what will change when commit is executed. The command shows changes in the context of the full configuration hierarchy, making it clear where in the configuration structure the changes will occur.

The show | compare command is a best practice to use before every commit, especially for complex configuration changes or in production environments where configuration errors could have significant impact. Administrators should review the compare output to ensure all changes are expected and correct. The command can also be used with rollback numbers to compare the candidate configuration with previous configurations, such as show | compare rollback 1 to see differences from the previous configuration. This comparison capability provides powerful configuration change tracking and verification, helping maintain configuration accuracy and preventing unintended changes from being activated.

Option A is incorrect because show changes is not a valid Junos command. The correct command includes the pipe symbol and compare keyword: show | compare.

Option B is incorrect because show diff is not the correct Junos syntax. While diff is a Unix command for comparing files, in Junos the correct command is show | compare.

Option D is incorrect because compare config is not a valid Junos command. Configuration comparison requires the show | compare command which uses the pipe mechanism to process show command output.

Question 89: 

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

A) To commit without validation

B) To require a second commit within a time period or automatically rollback

C) To commit and exit immediately

D) To commit only if no errors exist

Answer: B

Explanation:

The commit confirmed command in Junos activates configuration changes but requires a second confirming commit within a specified time period (default 10 minutes), or the configuration automatically rolls back to the state before the commit confirmed was executed. This safety mechanism protects administrators from configuration changes that might inadvertently lock them out of the device or cause connectivity issues that prevent further configuration access.

When commit confirmed is executed, the new configuration becomes active just like a normal commit, but Junos starts a timer. If the administrator does not execute another commit command (without the confirmed option) before the timer expires, the device automatically reverts to the previous configuration. This automatic rollback ensures that if a configuration change breaks connectivity or causes other problems that prevent the administrator from accessing the device, the device will recover automatically by returning to the known working configuration.

The commit confirmed command is particularly valuable when making changes that affect device management access, such as modifying management interface IP addresses, changing firewall rules that might block access, or altering routing that could affect reachability. The time period can be specified with the commit confirmed minutes syntax, such as commit confirmed 5 for a five-minute confirmation window. If the changes work correctly and the administrator can still access the device, they simply execute another commit command to confirm the changes and prevent the automatic rollback. This provides a reliable safety net that prevents administrators from accidentally locking themselves out of devices during configuration changes.

Option A is incorrect because commit confirmed does perform validation like any commit command. It does not skip validation checks; it simply adds an automatic rollback safety mechanism on top of normal commit behavior.

Option C is incorrect because commit and-quit is a different command that commits and exits configuration mode. Commit confirmed does not exit configuration mode and instead requires a subsequent confirming commit.

Option D is incorrect because all commit commands only proceed if no errors exist. The confirmed aspect relates to requiring a second commit for confirmation, not to error checking which is standard for all commits.

Question 90: 

Which command is used to save the current configuration to a file in Junos?

A) save configuration filename

B) show configuration | save filename

C) export config filename

D) write file filename

Answer: B

Explanation:

The command show configuration | save filename in operational mode (or show | save filename in configuration mode) is used to save the current configuration to a file in Junos. This command redirects the output of the show configuration command through the save pipe modifier, which writes the output to a specified file on the device’s file system. This capability is useful for creating configuration backups, documenting configurations, or preparing configurations for transfer to other devices.

The save modifier writes the configuration to a file in the /var/tmp/ directory by default unless a full path is specified. The filename can be specified with or without a path, and common practice is to use descriptive names that include dates or other identifying information. For example, show configuration | save /var/tmp/backup-config-2024-01-15.txt saves the complete configuration to a timestamped file. The saved file contains the configuration in text format as it would appear in the show configuration output, making it human-readable and suitable for documentation or later reference.

This file save capability is part of the broader pipe functionality in Junos that allows command output to be processed in various ways. In addition to save, other useful pipe modifiers include display set to show configuration in set command format before saving, and match or except to filter what gets saved. The saved configuration files can later be loaded, compared with current configurations, or used as templates for configuring other devices. Understanding how to save and manage configuration files is an important skill for configuration management, backup procedures, and disaster recovery planning in Junos environments.

Option A is incorrect because save configuration filename is not valid Junos syntax. Configuration saving requires using the show command with the pipe and save modifier.

Option C is incorrect because export config filename is not a valid Junos command. The correct method uses the show command with the pipe modifier to save output to a file.

Option D is incorrect because write file filename is not valid Junos syntax. While some network operating systems use write commands, Junos uses the show command with pipe modifiers for saving configuration output.