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Juniper JN0-106 Exam Prep
Junos, Associate (JNCIA-Junos) (Page 6 )

Updated On: 5-Oct-2026
Page 2 of 13
PDF with 98 Questions

Which statement accurately describes the purpose of route preference in Junos OS?

  1. It sets the metric for forwarding traffic through the Packet Forwarding Engine.
  2. It determines which route is selected as active when multiple routes to the same destination exist.
  3. It controls the redistribution of routes between routing instances.
  4. It determines the maximum number of routes that can be installed in the routing table.

Answer(s): B

Explanation:

In the Junos OS architecture, the routing table often receives prefix information from various sources, including direct connections, static configurations, and multiple dynamic interior and exterior gateway protocols. Route preference, frequently referred to as administrative distance in other vendor environments, serves as the primary tie-breaking mechanism used by the Routing Engine to select a single "active" route when multiple entries for the exact same destination prefix exist from different protocol sources. Each routing source is assigned a default numerical value, where a lower numerical value indicates a more preferred or "trustworthy" source. For instance, a direct route typically carries a preference of 0, while OSPF internal routes default to 10 and BGP routes default to 170.
The selection process evaluates these values; the route with the lowest preference is installed in the forwarding table and used for transit traffic. If preferences are equal, Junos secondary tie-breakers like local preference or metric are considered. Understanding this hierarchy is critical for traffic engineering and ensuring predictable routing behavior across the fabric. Modification of these default values via routing policy allows administrators to influence path selection without altering the underlying protocol metrics themselves.


Reference:

Routing Fundamentals, Route Preference Selection.



What is the purpose of an ARP packet?

  1. to determine the MPLS label of a given IP address
  2. to determine the IP address of a given URL
  3. to determine the MAC address of a given IP address
  4. to determine the IP address of a given MAC address

Answer(s): C

Explanation:

The Address Resolution Protocol (ARP) is a fundamental Layer 2 utility used within the IPv4 suite to resolve a known network-layer (Layer 3) address to its corresponding physical media access control (MAC) or hardware address (Layer 2). In a typical Ethernet environment, when a Junos device needs to forward a packet to a next-hop on a local subnet, the Packet Forwarding Engine (PFE) requires the destination MAC address to properly encapsulate the frame.
The process begins with an ARP Request, which is broadcast to all hosts on the segment asking, "Who owns this IP address?" The host assigned that specific IP responds with an ARP Reply containing its MAC address. The Junos device then stores this mapping in its ARP cache (viewable via the show arp command) to avoid repeated broadcasts for subsequent packets. This resolution is essential because while IP addresses facilitate end-to-end logical routing, the actual delivery of data across a physical wire or switch fabric relies entirely on hardware addresses. Without successful ARP resolution, the device cannot complete the Layer 2 header, and the traffic will be dropped as "encapsulation failed."


Reference:

Networking Fundamentals, Ethernet and Address Resolution Protocol.



Which protocol provides secure remote CLI access to a Junos device?

  1. FTP
  2. SNMP
  3. Telnet
  4. SSH

Answer(s): D

Explanation:

Securing the management plane is a core requirement for any Junos OS deployment. Secure Shell (SSH) is the industry-standard protocol used to provide encrypted, authenticated remote access to the Junos Command Line Interface (CLI). Unlike Telnet, which transmits both administrative credentials and command data in cleartext, SSH utilizes public-key cryptography to establish a secure tunnel, protecting the session from eavesdropping, man-in-the-middle attacks, and unauthorized interception.
In Junos OS, SSH is typically enabled within the [edit system services] hierarchy. Once active, it allows administrators to perform operational and configuration tasks with the assurance that their management traffic remains confidential. Beyond simple terminal access, SSH serves as the transport mechanism for other secure management functions, such as the NETCONF XML management protocol and Secure Copy (SCP) for file transfers. For high-security environments, Junos supports advanced SSH features including key-based authentication, strong cipher suites, and multi-factor authentication integration. Disabling insecure protocols like Telnet and FTP in favor of SSH and SFTP/SCP is a foundational best practice for hardening the Routing Engine against external threats.


Reference:

User Interfaces, Accessing the Junos CLI, System Services.



You want to automatically back up your Junos device configuration to an external server every time you commit a configuration change. In this scenario, which command would accomplish this task?

  1. set system commit synchronize
  2. set system archival configuration transfer-interval
  3. set system archival configuration transfer-on-commit
  4. set system archival configuration archive-sites

Answer(s): C

Explanation:

Junos OS provides robust automation features for configuration management, specifically through the system archival utility.
When an administrator needs to ensure that every successful configuration change is mirrored to an off-box repository for disaster recovery or auditing, the transfer-on-commit statement is the appropriate tool. This command instructs the Junos device to initiate an automated upload process immediately following the validation and activation of a commit command.
To fully implement this, the administrator must also define the archive-sites, which specify the destination URIs (using protocols such as FTP, SCP, or HTTP) and the necessary credentials for the external server.
While transfer-interval can be used to back up configurations on a chronological schedule (e.g., every 60 minutes), transfer-on-commit is superior for tracking specific change events as they happen. This ensures that the external backup is always synchronized with the current active configuration on the device. Once configured, the device handles the background transfer, allowing the administrator to maintain a historical record of configuration states without manual intervention, which is essential for large-scale operational environments.


Reference:

Configuration Basics, Managing Configurations, System Archival.



Which statement describes the primary purpose of a routing policy in Junos OS?

  1. It controls which routes are accepted or advertised by a routing protocol. B. It determines the physical interface used for forwarding traffic. C. It sets the maximum number of routes in the routing table. D. It enables automatic rollback of routing changes.

Answer(s): A

Explanation:

In Junos OS, a routing policy is a powerful tool used to manage the flow of routing information between the Routing Information Base (RIB) and routing protocols. Unlike forwarding decisions, which are handled by the Packet Forwarding Engine, routing policies function within the control plane on the Routing Engine. Their primary purpose is to define specific criteria for importing routes into the routing table from neighbors or exporting routes from the routing table to neighbors.
Routing policies consist of terms containing from (match) and then (action) statements. They allow administrators to filter prefixes (e.g., denying specific BGP routes), modify route attributes (e.g., changing OSPF metrics or BGP communities), and manipulate path selection behavior. For example, an export policy might be used to ensure that only specific internal subnets are advertised to an ISP via BGP, preventing the accidental leakage of private infrastructure addresses. By default, Junos applies "default policies" for each protocol (such as OSPF accepting all OSPF routes), but custom policies allow for granular control over how the device interacts with the rest of the network. This ensures that the routing table contains only the desired paths for optimal traffic engineering.


Reference:

Routing Policy and Firewall Filters, Policy Framework.



According to HPE Juniper Networking, when should you use the replace pattern command instead of the rename command?

  1. You want to create a private candidate configuration.
  2. You want to disable a physical interface.
  3. You need to edit a single component name in the configuration.
  4. You want to globally replace all occurrences of a specific string.

Answer(s): D

Explanation:

In Junos OS configuration management, the rename and replace pattern commands serve distinct roles for modifying the candidate configuration. The rename command is used when an administrator needs to change the identifier of a specific, single configuration object—such as changing an interface name or a policy-term name—while keeping the underlying properties of that object intact. In contrast, the replace pattern command is a powerful utility designed for bulk modifications across the configuration hierarchy. It utilizes string matching or regular expressions to find every occurrence of a specific text string and substitute it with another.
This is particularly useful in scenarios involving mass updates, such as migrating an entire subnet across multiple interface descriptions, firewall filters, and routing policy terms simultaneously.
While rename acts locally on a specific path, replace pattern can be applied globally from the root of the configuration or constrained to a specific sub-hierarchy. As a Senior Architect, it is critical to understand that replace pattern does not just change names; it can modify any part of the statement text, making it an essential tool for efficient large-scale configuration refactoring without the need for manual, line-by-line edits. Reference:
Configuration Basics, Modifying Configuration, Command Line Editing.



Which two statements are correct about a Routing Engine? (Choose two.)

  1. It processes management traffic.
  2. It processes CoS marked traffic.
  3. It forwards transit traffic.
  4. It maintains routing tables.

Answer(s): A,D

Explanation:

The architecture of a Junos device is bifurcated into two primary functional planes: the Control Plane, managed by the Routing Engine (RE), and the Data Plane, managed by the Packet Forwarding Engine (PFE). The Routing Engine serves as the "brain" of the device. One of its primary responsibilities is the processing of management traffic, which includes handling CLI sessions (SSH, Telnet), SNMP requests, and system logging. Because the RE runs the Junos OS kernel, it provides the environment for all administrative tasks and system management utilities.
Additionally, the Routing Engine is responsible for the intelligence of the network, which involves running routing protocols (such as OSPF, BGP, or IS-IS) and maintaining the master routing tables. It populates the Routing Information Base (RIB) with all learned paths and then calculates the best paths to build the Forwarding Information Base (FIB). This FIB is then pushed to the PFE for hardware-level packet switching. It is a common misconception that the RE handles transit traffic; however, the RE only handles "exception traffic" or traffic destined for the device itself. This separation ensures that the control plane remains stable and responsive even during periods of heavy transit load on the forwarding plane. Reference:
Junos OS Fundamentals, Architectural Overview, Control Plane vs. Forwarding Plane.



After the factory default configuration is loaded, which configuration object must be created prior to the first commit?

  1. host name
  2. loopback IP address
  3. out-of-band connectivity
  4. root authentication

Answer(s): D

Explanation:

When a Junos device is initialized with its factory default configuration, it essentially exists in a "blank slate" state with minimal operational parameters. The most critical security requirement imposed by Junos OS during this initial setup phase is the mandatory configuration of a root-level password. Specifically, the root-authentication object must be defined within the [edit system] hierarchy before the system will allow the candidate configuration to be successfully committed for the first time.
This is a built-in safety mechanism designed to prevent the device from being deployed in an insecure state with an empty administrative password. If an administrator attempts to execute a commit command without having set the root password, the Junos OS parser will return an error and fail the commit process.
While setting a host name or configuring management interfaces are best practices for operational readiness, they are not strictly required by the Junos commit-check logic. Only the root-authentication (typically a plain-text password or an encrypted string) is a hard prerequisite to transition the device from the factory-default state to an active, running configuration. Reference:
Configuration Basics, Initial Configuration, Security Requirements.



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