Juniper JN0-105 Junos - Associate (JNCIA-Junos) 2025 Exam Exam Practice Test

To recover the root password on a Junos router without losing the configuration, you should (A) enter and commit the new root password once you have gained access to the system, (D) hit the space bar to interrupt the boot process and enter recovery mode when prompted during the boot process, and (E) use a console connection to reboot the device and access the bootloader prompt. These steps allow you to reset the root password while preserving the existing configuration.

When you enter ? at the command-line prompt in Junos OS, the system provides assistance in two significant ways. Firstly, it lists the available commands and options that can be used at the current point in the command hierarchy, aiding users in understanding what commands they can execute next. Secondly, it displays summary information about those commands and options, providing brief descriptions or additional context that can help users understand the function of each command or option. This feature is particularly useful for learning the command structure or for quick reference when specific command syntax is forgotten.

When configuring the system-related settings for the current date and time on a Junos device, especially for a specific time zone like America/Los_Angeles, and the time does not automatically adjust, two effective actions can be taken. Firstly, setting the date and time manually allows for immediate correction of the system clock. This can be done via the CLI with the appropriate set date and time command. Secondly, configuring the device to use an NTP server can provide ongoing synchronization with an accurate time source, ensuring that the device maintains the correct time and date automatically in the future, even in the case of restarts or minor drifts in the internal clock.

The Packet Forwarding Engine (PFE) in Junos OS performs several key functions, including implementing firewall filters (A) and forwarding transit traffic (C). The PFE applies firewall filter rules to incoming and outgoing traffic and is responsible for the high-speed forwarding of packets based on the information in the forwarding table.

Implementing Class of Service (CoS) in a network provides numerous benefits, particularly in managing traffic based on its importance, source, or type. CoS enables network administrators to manage traffic congestion by applying various queuing techniques and policies to ensure that critical services remain unaffected during high congestion periods. Additionally, CoS allows for the prioritization of latency-sensitive traffic such as voice and video, ensuring that these services maintain quality despite varying network conditions.

In the default configuration of a Junos device, the primary system log file is "messages" (B). This log file contains a wide range of system messages, including operational status changes, system errors, and other critical information, making it a key resource for troubleshooting and monitoring the system's health.

In a Juniper Networks device, the Packet Forwarding Engine (PFE) processes unicast traffic by forwarding it according to the existing entries in the forwarding table. When the PFE encounters unicast traffic destined for an address that has a corresponding entry in the forwarding table, it directs the traffic through a specific outgoing interface or port toward its destination. This process is based on the most efficient path determined by the routing protocols in use, ensuring that the packet reaches its intended destination through a singular path, unless specific configurations such as load balancing are in place.

The forwarding table in a network device requires specific information to efficiently forward traffic toward its destination. This includes the next hop IP address, which indicates the next router or device in the path to the destination. The outgoing interface name identifies the physical or logical interface through which the packet should be sent to reach the next hop. Lastly, the next hop MAC address is crucial for Layer 2 forwarding decisions, allowing the device to encapsulate the IP packet in a frame that can be understood by Ethernet or other Layer 2 protocols. OSPF metric values and BGP local preference values are used in the routing decision process to select the best path and populate the forwarding table but are not directly used by the forwarding table to forward traffic.

Traceoptions in Junos OS are used for detailed debugging and troubleshooting of protocols and processes within the system. They are not enabled by default due to the potential performance impact and volume of data generated. Instead, traceoptions are enabled through specific configuration settings under the relevant protocol or process hierarchy. This allows administrators to target their troubleshooting efforts and control the scope of logging. By default, the output generated by traceoptions is stored in files located in the /var/log directory, with the file name typically specified in the traceoptions configuration. This structured approach to logging and debugging helps in diagnosing complex issues without overwhelming the system or the administrator with irrelevant data.

In Junos OS, remote access to the device's CLI is commonly facilitated through Secure Shell (SSH), a protocol providing secure command-line access over an insecure network. The given exhibit indicates an attempt to set a root authentication password but does not show configuration for enabling remote access services. To enable SSH, which is not shown in the configuration snippet, you need to configure the device to accept SSH connections. This is done by enabling the SSH service within the system services hierarchy of the configuration. The correct command to add to the existing configuration for enabling remote CLI access via SSH is set system services ssh. This command activates the SSH service, allowing secure remote logins to the device.

MAC (Media Access Control) addresses are unique identifiers assigned to network interfaces for communications at the data link layer of a network segment. MAC addresses are used to identify the physical hardware on a network. In the context of Ethernet switches, the destination MAC address in incoming frames is used to determine the appropriate output port for forwarding the frame towards its final destination. The switch does not change the destination MAC address; it uses the MAC address to make forwarding decisions within the local network segment.

Referring to the firewall filter configuration in the exhibit, when a packet matches the specified term limit-icmp, two actions are defined in the then statement: count count-icmp and discard. The count count-icmp action means that each time a packet matches this term, a counter named count-icmp will be incremented, providing a tally of how many packets have matched the term. The discard action means that the packet will be dropped and not forwarded through the device. This effectively prevents the packet from reaching its intended destination. There is no action specified that would cause an ICMP destination unreachable message to be returned, nor is there any action that would allow the packet to be forwarded.

Transit traffic that traverses the forwarding plane of a Layer 3 router includes both unicast and multicast traffic types. Unicast traffic is directed from a single source to a single destination, while multicast traffic is sent from one source to multiple destinations that are part of a multicast group. These types of traffic are efficiently routed through the network by leveraging the router's forwarding plane capabilities. Exception traffic, which requires special handling by the control plane, and broadcast traffic, which is typically limited to a single broadcast domain and not usually forwarded by Layer 3 routers, are not considered standard types of transit traffic for the forwarding plane of a router.

Class of Service (CoS) in Junos OS provides tools for managing traffic congestion and ensuring that latency-sensitive traffic is given priority over less time-critical data. By implementing CoS, network administrators can classify traffic into different priority levels, apply scheduling policies to ensure that high-priority traffic is transmitted first, and use congestion management techniques such as queue buffers and drop profiles. This helps in maintaining the quality of service for critical applications, especially during periods of high network congestion. However, CoS does not eliminate congestion entirely nor does it inherently make the network faster; it provides a mechanism for better managing and controlling traffic flows according to their importance and time sensitivity.

When creating a new policy to accept and redistribute routes into your Interior Gateway Protocol (IGP), the route-filter match criteria is used to identify the route prefixes to select. The route-filter statement specifies which prefixes should be matched in a policy. This allows for precise control over which routes are accepted and redistributed, facilitating efficient and secure routing policies within the network.

References:

"show | display set | match ge-0/0/2" indicating command examples and match criteria from Useful Juniper Commands.txt​​.

Juniper official documentation: Routing Policy and Firewall Filters Configuration Guide.

In Juniper Networks devices, firewall filters are used to control packet flow through the device. The default action for packets that do not match any of the specified criteria in the firewall filter is to discard them, enhancing network security by ensuring that only explicitly allowed traffic can pass through. Furthermore, it is possible to configure multiple firewall filters on a device, allowing for granular control over traffic based on various criteria such as source, destination, and protocol type.

Layer 2 network switches are crucial components in local area networks (LANs), providing multiple functions for data packet forwarding and network segmentation. One inherent characteristic of switches is their susceptibility to traffic loops, especially in networks with redundant paths. Without proper loop prevention protocols like Spanning Tree Protocol (STP), loops can cause broadcast storms and network instability. Additionally, switches inherently flood broadcast traffic to all ports within the broadcast domain, except the port on which the broadcast was received. This is because broadcast frames are meant to be delivered to all devices within the VLAN, and the switch ensures this by flooding these frames to all ports in the VLAN, except the source port.

Junos OS can store up to 50 rollback configuration files, making B the correct answer. These rollback files allow administrators to revert to previous configurations, providing a safety net that facilitates recovery from configuration errors or undesired changes

In Junos OS, when creating a new user account, the minimum required fields are the username and the login class. The username is the identifier for the account, while the login class specifies the level of access or permissions the user has on the device. Login classes allow for the differentiation between various roles, such as read-only access or full administrative rights. Other information, such as full name or user ID, is optional and not strictly necessary for the creation of a functional user account.

In Junos OS, the management daemon (mgd) is responsible for handling all the device management tasks, including processing CLI commands and handling commit operations. The mgd daemon interacts with the Junos OS configuration database and provides the necessary logic to ensure that configuration changes are syntactically correct and do not conflict with each other. When a user commits a configuration, mgd validates the changes, applies them to the running configuration, and ensures that the necessary daemons are notified of the changes to apply them accordingly.

In Junos OS routing policy evaluation, "next policy" (A) and "next term" (C) are common actions that affect the flow of policy evaluation. "Next policy" directs the evaluation to the next policy in the sequence, whereas "next term" moves the evaluation to the next term within the current policy, allowing for granular control over routing decisions.

Operating an Interior Gateway Protocol (IGP) within an Autonomous System (AS) provides several benefits, including determining the optimal paths for data transmission (B), reacting quickly to network changes (D), and learning all about the subnets and best paths within the network (E). IGPs are designed to manage routing within a single AS efficiently, adapting to changes and ensuring data is routed through the best available paths.

To advertise a default static route into OSPF on router R1, a routing policy should be configured. This policy would typically include a statement to match the default route (0.0.0.0/0) and then apply an action to set the route as an OSPF external type, which would then be redistributed into the OSPF domain. The routing policy is a set of conditions and actions that determine how routes are imported into or exported from the routing table and how routes are shared between routing instances or routing protocols. After defining the policy, it must be applied to OSPF under the export section of the OSPF configuration on R1. This process will allow R1 to announce the default route to other OSPF routers in the network, which then can use it as a gateway of last resort to reach the Internet or other networks not explicitly known to the OSPF domain.

The Routing Engine (RE) in Junos OS has several critical functions, including processing all management traffic (A) and running the Junos operating system (B). The RE handles system management tasks, user interfaces, system services, and routing protocol processes. It does not directly process transit traffic or evaluate firewall filters for transit traffic, as these tasks are handled by the Packet Forwarding Engine (PFE).

Junos OS selects routes based on the route preference (also known as administrative distance). Static routes typically have a lower route preference than OSPF routes, meaning they are more preferred. Since the static route to 192.168.36.1/32 is shown with a preference of 5, it will be selected over the OSPF route for packet forwarding, assuming no other factors such as route filters or policies affect the routing decision.

In Junos OS, when a user issues the configure exclusive command, it locks the candidate configuration for that user, preventing other users from making concurrent configuration changes. This exclusive lock ensures that configuration changes are managed in a controlled manner, reducing the risk of conflicting changes. As a result, while one user is in exclusive configuration mode, other users are prevented from entering configuration mode until the lock is released, either by the user committing the changes or exiting configuration mode.

The routing table and forwarding table play distinct roles in a Junos OS device. The correct answers are A and D. The routing table (A) is used by the Routing Engine (RE) to select the best route among all the learned routes, while the routing table (D) stores all routes and prefixes learned from all routing protocols. The forwarding table, in contrast, contains only the active routes chosen by the RE and is used by the Packet Forwarding Engine for actual packet forwarding.

The Routing Protocol Daemon (rpd) in Junos OS is responsible for maintaining routing protocols and tables. It handles all routing information, including the calculation of routes and the population of the routing table, making it crucial for dynamic routing operations.

The Packet Forwarding Engine (PFE) in Junos OS is responsible for maintaining the forwarding table. The PFE processes incoming packets, performs route lookups in the forwarding table, and forwards packets based on this information, offloading these tasks from the Routing Engine to ensure efficient packet forwarding.

If you've committed a configuration and then need to revert to the previous configuration, the rollback command is used. Since the incorrect IP address has not been committed, as indicated by the commit check command being successful, issuing rollback 1 will undo the changes made in the current session, which includes the accidental entry of the IP address.