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JN0-105 Juniper Practice Test Questions and Exam Dumps

Question No 1:

Which two statements are correct regarding Layer 2 network switches? (Choose two.)

A Switches flood broadcast traffic.
B Switches are susceptible to traffic loops.
C Switches do not learn MAC addresses.
D Switches create a single collision domain.

Correct Answer: A, B

Explanation:

Layer 2 network switches operate at the Data Link Layer of the OSI model, primarily responsible for forwarding Ethernet frames based on MAC addresses. They are essential in managing traffic within a local area network (LAN). Let’s examine the correct and incorrect statements about Layer 2 switches:

A. Switches flood broadcast traffic
This is a correct statement. When a switch receives a broadcast frame, it floods the frame to all ports except the port on which the frame was received. This behavior is necessary because the switch does not initially know where the destination device is located within the network. Broadcasting ensures that all devices in the network segment receive the frame. Broadcast frames are typically used for operations like ARP requests, where the sender does not know the destination MAC address.

B. Switches are susceptible to traffic loops
This is also correct. Layer 2 switches are vulnerable to traffic loops if there are multiple active paths between switches. This can occur in networks with redundant links, which, if not properly managed, can lead to loops in the network. These loops result in broadcast storms, where broadcast traffic circulates endlessly, consuming bandwidth and potentially causing network outages. To prevent this, Spanning Tree Protocol (STP) is often implemented to detect and eliminate loops by blocking redundant paths.

Now let’s look at the incorrect statements:

C. Switches do not learn MAC addresses
This is incorrect. One of the core functionalities of Layer 2 switches is to learn MAC addresses. When a switch receives a frame, it examines the source MAC address and records the port from which it came in its MAC address table (also called a forwarding table). This enables the switch to forward frames to the correct port in the future, improving network efficiency by reducing unnecessary flooding of frames.

D. Switches create a single collision domain
This is also incorrect. Switches segment collision domains rather than creating a single collision domain. Each port on a switch represents its own collision domain. This means that devices connected to different ports of the same switch do not experience collisions with each other. Switches are designed to isolate traffic between devices, so a collision domain exists only on the shared medium before a switch (like a hub or network segment), not after the switch. This helps to eliminate collisions that are common in hubs.

In summary, the correct statements are that switches flood broadcast traffic (A) and switches are susceptible to traffic loops (B). These are important aspects of switch operation that network administrators need to understand and manage, especially in larger or more complex network topologies.

Question No 2:

Which two attributes are characteristics of the UDP protocol? (Choose two.)

A UDP is best effort.
B UDP is always slower than TCP.
C UDP is connectionless.
D UDP is more reliable than TCP.

Correct answer: A and C

Explanation:

The User Datagram Protocol (UDP) is one of the core transport layer protocols in the Internet Protocol Suite, primarily known for its simplicity and low overhead. To understand the correct attributes of UDP, let’s examine each option:

A. UDP is best effort: This is true. UDP operates on a "best-effort" basis, meaning it does not guarantee delivery of packets, nor does it perform error checking or correction beyond a simple checksum. It sends packets without establishing a connection, and it does not attempt to recover lost packets. This is in contrast to protocols like TCP, which offer reliability through retransmissions, acknowledgment, and flow control. UDP’s "best-effort" nature makes it suitable for applications where speed is crucial and occasional data loss is acceptable, such as streaming, VoIP, and online gaming.

B. UDP is always slower than TCP: This is incorrect. In fact, UDP is often faster than TCP due to its lack of connection establishment, error recovery, and congestion control mechanisms. TCP’s overhead, which includes managing connections, ensuring reliable delivery, and reordering packets, can slow it down compared to UDP, which has minimal protocol overhead and no reliability features. Therefore, UDP’s performance advantage typically comes from its lightweight nature, which is why it’s preferred in real-time applications.

C. UDP is connectionless: This is true. UDP is a connectionless protocol, meaning it does not require a connection to be established between the sender and receiver before data transmission begins. Each UDP packet (datagram) is sent independently, and there is no formal session or handshake as there is with TCP. This connectionless nature allows UDP to transmit data with less overhead, making it suitable for applications that need fast transmission of data without waiting for acknowledgments.

D. UDP is more reliable than TCP: This is incorrect. UDP is not more reliable than TCP; in fact, it is considered less reliable because it does not guarantee that data will be delivered to the destination or that it will arrive in the correct order. It does not perform any error checking beyond the checksum or provide mechanisms for retransmitting lost packets. In contrast, TCP ensures reliability by performing error detection, acknowledging received data, and retransmitting lost packets, which makes it a more reliable protocol for critical applications.

In summary, the two correct attributes of the UDP protocol are that it is best effort (A) and connectionless (C). These characteristics make UDP well-suited for applications where speed is a priority and occasional data loss can be tolerated, such as live video streaming or online gaming.

Question No 3:

You are unable to remotely access your Juniper device using the CLI. Given the exhibit, which command would you add to the existing configuration to enable remote CLI access?

A set system services ssh
B load factory-default
C set system login idle-timeout 20
D set system root-authentication plain-text-password

Correct Answer: A

Explanation:

In this scenario, the issue involves enabling remote CLI access to the Juniper device. When we talk about enabling remote CLI access over a network, the most common and secure way is to use SSH (Secure Shell), which allows for encrypted and secure management of network devices.

• A (set system services ssh): This is the correct command to enable SSH on a Juniper device. It configures the device to accept remote management via SSH, which is necessary for remote CLI access. Without this, you will not be able to securely access the device remotely using the command-line interface.

Here’s why the other options are not suitable for this specific purpose:

• B (load factory-default): This command is used to reset the Juniper device to its factory default settings. While this might resolve configuration issues by wiping out any previous configurations, it does not directly address enabling remote CLI access and may not be appropriate unless you're starting fresh with a new configuration.

• C (set system login idle-timeout 20): This command configures the idle timeout for the login session, meaning that if no activity occurs for 20 minutes, the session will be terminated. While this command can help control how long an idle session remains active, it does not enable remote CLI access itself.

• D (set system root-authentication plain-text-password): This command sets the root password for authentication, but using plain-text passwords is not recommended due to security concerns. This command is related to authentication but does not enable remote access by itself. It may help in ensuring the root account is configured correctly, but SSH must still be enabled for remote access.

Therefore, A (set system services ssh) is the correct command to add to your configuration in order to enable remote access via SSH to the Juniper device’s CLI. After executing this command, the device will be ready to accept secure remote connections over the network, which is the standard method for remote management.

Question No 4:

You are trying to diagnose packet loss at interface ge-0/0/3. Which command would help you view error statistics in real time?

A monitor interface ge-0/0/3
B show interface ge-0/0/3
C show interface terse
D monitor interface traffic

Correct answer: A

Explanation:

When diagnosing network issues such as packet loss, it's important to view interface statistics in real time to understand the health and performance of the interface. The following analysis of each option will help identify the correct approach:

Option A: monitor interface ge-0/0/3
This command provides real-time monitoring of the specified interface (ge-0/0/3 in this case). By using the monitor interface command, you can observe live traffic on the interface, including error statistics such as packet loss, discards, and other performance metrics. It continuously displays the current status, which is particularly useful for diagnosing transient issues such as packet loss that may not be evident in static outputs. Therefore, this is the most appropriate command for viewing error statistics in real time.

Option B: show interface ge-0/0/3
The show interface command displays detailed information about the interface, such as operational status, traffic statistics, and errors. While this command is useful for diagnosing network issues and provides error statistics, it is not real-time; it provides a snapshot of the current interface status at the moment the command is run. For continuous, real-time monitoring, monitor interface is the better option.

Option C: show interface terse
The show interface terse command gives a summarized view of interface statistics across the device, providing a high-level summary of status and traffic. However, it doesn't provide real-time monitoring or the level of detail needed for diagnosing packet loss at a specific interface. It can be helpful for quickly viewing the overall health of interfaces, but it is not designed for real-time error tracking.

Option D: monitor interface traffic
This command is not typically used in standard network device configurations. While it might appear to be a useful option for traffic monitoring, it's not the correct command for error statistics or real-time monitoring of interface issues such as packet loss.

In summary, Option A, monitor interface ge-0/0/3, is the best choice for real-time monitoring of error statistics on the interface. It allows you to continuously observe the behavior of the interface and diagnose packet loss as it occurs, making it the most suitable command for this scenario.

Question No 5:

Which prompt indicates that you are using configuration mode?

A >
B $
C #
D %

Correct answer: C

Explanation:

In networking devices such as Cisco routers and switches, the prompt character displayed at the command line interface (CLI) indicates the mode in which the device is currently operating. When you are in configuration mode, the prompt will display a # symbol. This prompt is seen after you enter global configuration mode from the privileged EXEC mode.

Here's a breakdown of what each prompt represents:

A – >:
This symbol typically represents the user EXEC mode on Cisco devices. In this mode, you have limited access to the system’s configuration and can execute basic commands, such as checking device status. It is a restrictive mode that does not allow for configuration changes.

B – $:
The $ symbol is not a standard prompt used on Cisco devices. It is more commonly seen in Unix-like operating systems (such as Linux) or in certain script environments. This is not associated with network device configuration modes.

C – #:
The # symbol indicates that the device is in global configuration mode or a more specific configuration mode, such as interface configuration mode. In this mode, you can make changes to the configuration of the device, such as modifying routing protocols, interface settings, or security configurations.

D – %:
The % symbol is typically seen in user EXEC mode on Cisco devices, but in some cases, it can also appear in certain error messages. It is not used to indicate that the device is in configuration mode.

Therefore, when you see the # prompt, you know that the device is in configuration mode, and you can begin making changes to the device’s configuration. This is the defining characteristic of global configuration mode. Thus, the correct answer is C.

Question No 6:

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

A It processes CoS marked traffic.
B It processes management traffic.
C It maintains routing tables.
D It forwards transit traffic.

Correct Answer: B and C

Explanation:

A Routing Engine (RE) plays a crucial role in the overall function of a router or network device, performing key tasks related to network management, routing, and control-plane operations.

• B. It processes management traffic: The Routing Engine is responsible for handling control and management tasks, including processing management traffic. This traffic typically includes administrative tasks such as configurations, monitoring, and maintenance commands sent to the device. The RE ensures that the management plane, such as SNMP or CLI interactions, is processed correctly.

• C. It maintains routing tables: One of the primary responsibilities of the Routing Engine is to maintain and update the routing tables. The Routing Engine receives and processes routing information from routing protocols like OSPF, BGP, or RIP, and stores the best paths in the routing tables. These tables are then used to determine how data packets should be forwarded across the network.

Let’s break down the other options:

• A. It processes CoS marked traffic: CoS (Class of Service) marked traffic is generally managed by the Forwarding Engine (FE), not the Routing Engine. The FE is responsible for making forwarding decisions based on the routing information and Quality of Service (QoS) markings, such as CoS or DSCP. The Routing Engine focuses more on control-plane tasks like maintaining routing information, not on forwarding data based on CoS markings.

• D. It forwards transit traffic: Transit traffic (data being forwarded across the network) is handled by the Forwarding Engine, not the Routing Engine. The Routing Engine is involved in control-plane operations, while the Forwarding Engine handles the data-plane tasks, such as forwarding packets based on the routing information provided by the RE.

Thus, B and C are the correct answers because they accurately reflect the responsibilities of the Routing Engine in maintaining routing tables and processing management traffic, both of which are core control-plane functions.

Question No 7:

What are two methods for navigating to configuration mode from an operational mode prompt? (Choose two.)

A. Use the quit command
B. Use the configure command
C. Use the exit command
D. Use the edit command

Correct answer: B, D

Explanation:

In many network devices, particularly those running Junos OS (such as Juniper routers and switches), users interact with the device through two primary modes: operational mode and configuration mode. Transitioning between these modes is essential for both monitoring the system (in operational mode) and making configuration changes (in configuration mode).

• Use the configure command (option B) is the most common method for navigating from the operational mode to the configuration mode in Junos OS. When you enter the configure command at the operational prompt, the system switches to configuration mode, allowing you to make configuration changes to the device.

• Use the edit command (option D) is another method, often used in a slightly different context. The edit command is typically used in some platforms or CLI configurations (such as Junos) to move to a specific hierarchical level within the configuration structure. By using the edit command, you enter the configuration mode and start editing specific configuration branches. This is another valid method of entering configuration mode, particularly when you need to go directly to a certain part of the configuration hierarchy.
  
  

The other options, quit (option A) and exit (option C), are used to navigate away from configuration or operational modes, not to enter configuration mode:

• Quit command (option A) is used to exit out of various sub-menus or lower levels within the system, but it does not transition you to configuration mode. It is often used to exit from the configuration mode or return to a higher-level prompt.

• Exit command (option C) is similar to quit and is used to leave configuration mode or a sub-mode, returning to the operational mode or higher-level prompt. It also doesn't serve to enter configuration mode.

Thus, the correct methods for navigating to configuration mode from the operational mode prompt are B and D.

Question No 8:

Which statement is correct concerning exception traffic processing?

A. Exception traffic is discarded by the PFE.
B. Exception traffic is rate-limited to protect the RE.
C. Exception traffic is always dropped during congestion.
D. Exception traffic is never forwarded.

Correct Answer: B

Explanation:

Exception traffic refers to traffic that cannot be handled in the normal forwarding path by the router's Packet Forwarding Engine (PFE). This type of traffic typically requires special handling by the Routing Engine (RE) due to its unique characteristics, such as errors, specific control traffic, or packets that need to be processed by software rather than hardware.

Let's break down each option:

A. Exception traffic is discarded by the PFE.
This statement is incorrect. Exception traffic is typically forwarded to the RE for further processing rather than being discarded outright by the PFE. The PFE handles normal traffic forwarding but may route exception traffic to the RE for software-based processing if necessary.

B. Exception traffic is rate-limited to protect the RE.
This statement is correct. Exception traffic is often rate-limited to protect the RE, which has a much lower processing capacity than the PFE. If the RE were overwhelmed with exception traffic, it could degrade the performance of the router. Rate-limiting ensures that the RE can handle the load without being overwhelmed, and that critical functions of the router continue to operate efficiently.

C. Exception traffic is always dropped during congestion.
This statement is not correct. While it's true that network congestion can lead to packet drops, exception traffic is not automatically dropped during congestion. The router may choose to drop some traffic, but this decision depends on the router's policies and configurations, not an inherent property of exception traffic.

D. Exception traffic is never forwarded.
This is incorrect. Exception traffic is forwarded to the RE for processing. It is not typically dropped or ignored unless configured to do so under specific conditions, such as severe congestion or intentional blocking based on security policies.

Thus, the correct answer is B, as exception traffic is rate-limited to protect the RE, ensuring that it is not overwhelmed by traffic that needs to be processed in software.

Question No 9:

In the Junos OS, which keyboard shortcut allows you to move to the start of the line?

A. Ctrl+e
B. Ctrl+a
C. Ctrl+k
D. Ctrl+w

Correct Answer: B

Explanation:

In the Junos OS, as in many other Unix-like operating systems, keyboard shortcuts are designed to help users navigate and edit the command line efficiently. The shortcut that allows a user to move to the start of the line is Ctrl+a. This shortcut is commonly used in command-line interfaces to quickly return to the beginning of the current command or line.

Let's go through the other options to clarify why they are incorrect:

• A. Ctrl+e: This shortcut moves the cursor to the end of the line, not the beginning. It’s a common shortcut used to quickly navigate to the end of the current command line, which can be useful for editing at the end of a long command.

• C. Ctrl+k: This keyboard shortcut is used to delete everything from the cursor position to the end of the line. It is useful for clearing out unwanted text to the right of the cursor, but it does not move the cursor to the start of the line.

• D. Ctrl+w: This shortcut deletes the word before the cursor. It is used for quick text editing when you want to remove a whole word to the left of the cursor. It doesn't affect the cursor's position relative to the start of the line.

Thus, Ctrl+a is the correct shortcut to move the cursor to the start of the line in the Junos OS.

Question No 10:

Which two statements apply to the Routing Engine functions? (Choose two.)

A. It does not process routing updates.
B. It responds to ping and traceroute commands.
C. It maintains the routing tables.
D. It processes the transit traffic.

Correct Answer: B, C

Explanation:

The Routing Engine (RE) is an essential component in network devices such as routers. It handles a variety of tasks related to network management, routing, and control. Let’s go through the statements to understand which ones apply to its functions.

• A. It does not process routing updates: This statement is incorrect. The Routing Engine is responsible for processing routing updates. It handles the dynamic routing protocols (such as OSPF, BGP, or RIP), which includes learning, updating, and maintaining the routing information. The statement suggests the RE does not handle routing updates, but that is actually one of its core tasks.

• B. It responds to ping and traceroute commands: This statement is correct. The Routing Engine does indeed respond to diagnostic commands like ping and traceroute. These commands help administrators check the status and connectivity of the network. The RE manages the administrative control and can respond to such requests.

• C. It maintains the routing tables: This statement is correct. The Routing Engine maintains and updates the routing tables. These tables are used to determine the most efficient paths for routing traffic within the network. The RE plays a critical role in this process, keeping the routing tables up to date based on the latest routing protocol updates.

• D. It processes the transit traffic: This statement is incorrect. The Routing Engine does not process transit traffic. Transit traffic refers to the data packets that pass through the router as part of the forwarding process. The Packet Forwarding Engine (PFE) is responsible for this task, not the RE. The RE is more focused on routing control and administrative functions, while the PFE handles the actual packet forwarding.

In summary, the Routing Engine's main functions include responding to network diagnostic commands (such as ping and traceroute) and maintaining the routing tables, making options B and C the correct answers.