Juniper JN0-105 Exam Dumps & Practice Test Questions

Question 1:

Which two statements accurately describe the behavior and characteristics of Layer 2 switches? (Choose two.)

A Switches forward broadcast frames to all ports.
B Switches can experience network loops without safeguards.
C Switches do not maintain a MAC address table.
D Switches create one large collision domain for all connected devices.

Answer: A, B

Explanation:

Layer 2 switches operate at the Data Link layer of the OSI model and play a fundamental role in forwarding Ethernet frames within a LAN based on MAC addresses. Understanding their operational characteristics is critical for network design and troubleshooting.

A. Switches forward broadcast frames to all ports:
This statement is correct. When a Layer 2 switch receives a broadcast frame, it does not know the destination device’s exact location and therefore floods the broadcast frame out of all ports except the one it came from. This flooding behavior ensures that all devices in the broadcast domain receive the frame. Broadcast traffic is common for protocols such as ARP (Address Resolution Protocol), which relies on broadcasts to resolve IP addresses to MAC addresses.

B. Switches can experience network loops without safeguards:
This is also correct. Because switches often have redundant links for fault tolerance, multiple active paths between switches can cause loops at Layer 2. These loops result in broadcast storms, where broadcast frames circulate endlessly, overwhelming network bandwidth and causing serious outages. To prevent this, protocols like Spanning Tree Protocol (STP) are used to detect and block redundant paths, eliminating loops and stabilizing the network.

C. Switches do not maintain a MAC address table:
This is false. Switches learn MAC addresses by inspecting the source address of incoming frames and recording which port they arrive on. This MAC address table enables switches to forward unicast frames efficiently, reducing unnecessary flooding.

D. Switches create one large collision domain for all connected devices:
This is also false. Switches segment collision domains by creating a separate collision domain for each switch port. Unlike hubs, which share a single collision domain, switches isolate devices to prevent collisions, improving network performance.

In summary, the correct descriptions are that Layer 2 switches flood broadcast traffic and are vulnerable to loops if proper protocols are not in place. These behaviors are foundational to how switches manage LAN traffic.

Question 2:

Which two characteristics accurately describe the User Datagram Protocol (UDP)? (Choose two.)

A UDP delivers packets on a best-effort basis without guaranteed delivery.
B UDP is slower than TCP due to lack of error handling.
C UDP is a connectionless transport protocol.
D UDP provides more reliable data delivery than TCP.

Answer: A, C

Explanation:

UDP is a core transport layer protocol used for applications where speed and low overhead are prioritized over reliability. Understanding UDP’s properties helps in choosing the right protocol for specific network applications.

A. UDP delivers packets on a best-effort basis without guaranteed delivery:
This is correct. UDP does not provide acknowledgments, retransmissions, or error correction mechanisms beyond a basic checksum. It sends datagrams without ensuring they reach the destination or arrive in order. This “best-effort” delivery model is suitable for applications like live streaming, VoIP, and gaming, where timely delivery is more important than perfect accuracy.

C. UDP is a connectionless transport protocol:
This is also correct. Unlike TCP, UDP does not establish a connection or session before transmitting data. Each UDP packet is sent independently, and there is no handshake or formal connection setup. This reduces latency and protocol overhead, enabling faster data transmission.

Now, why the other options are incorrect:
B. UDP is slower than TCP due to lack of error handling:
This is false. UDP is typically faster than TCP because it avoids the overhead of connection setup, acknowledgments, retransmissions, and flow control that TCP requires. TCP’s reliability features add delay and processing time, making it slower in comparison.

D. UDP provides more reliable data delivery than TCP:
This is incorrect. UDP does not guarantee data delivery, sequencing, or retransmission of lost packets. TCP is designed for reliability, ensuring data is delivered intact and in order.

In conclusion, UDP’s best-effort and connectionless nature make it ideal for time-sensitive applications that can tolerate some data loss, whereas TCP is preferred when reliability is critical.

Question 3:

You cannot access your Juniper device remotely through the command-line interface (CLI). Based on the provided configuration, which command should be added to enable remote CLI access securely?

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:

When you need to remotely manage a Juniper device via its CLI, enabling a secure remote access method is essential. The standard, secure protocol for this purpose is SSH (Secure Shell), which encrypts communication and prevents unauthorized access or interception.

The command set system services ssh activates the SSH service on the Juniper device. This means the device will start accepting incoming SSH connections, allowing administrators to securely connect to the CLI from remote locations. Without enabling SSH, remote CLI access is not possible or secure, making this the fundamental step for remote management.

Now, let’s understand why the other options don’t fit this need:

• load factory-default (B) resets the device’s configuration to its original factory state. While useful for troubleshooting or starting fresh, it does not specifically enable remote access. Also, it can erase valuable configurations, so it is not recommended just to enable remote CLI access.

• set system login idle-timeout 20 (C) configures an idle timeout, automatically disconnecting inactive sessions after 20 minutes. Although important for security, it does not enable or facilitate remote access itself.

• set system root-authentication plain-text-password (D) sets the root password, but in plain text, which is insecure. While authentication is necessary, this command alone won’t enable remote connections, and it’s best practice to use encrypted authentication methods.

In summary, to allow secure remote CLI access to a Juniper device, enabling the SSH service via set system services ssh is the correct and necessary step. This command ensures encrypted, secure remote connections, making it the essential command in this context.

Question 4:

You suspect packet loss on interface ge-0/0/3 and want to monitor error statistics live. Which command provides real-time statistics for that interface?

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:

Diagnosing packet loss effectively requires live monitoring of interface performance to capture transient errors and traffic abnormalities as they happen. The command monitor interface ge-0/0/3 provides continuous, real-time feedback about the interface status, including error counts, packet drops, and traffic rates.

Real-time monitoring is crucial because packet loss may be sporadic or intermittent, and static snapshots from other commands might miss these brief events. This command continuously streams updates, giving network engineers instant insight into any problems on the specified interface.

Looking at the other options:

• show interface ge-0/0/3 (B) displays detailed interface statistics and error counters at the moment the command is run. It’s a snapshot of the current state, useful for diagnosis, but it does not update continuously, so it might miss short-lived issues.

• show interface terse (C) offers a brief summary of all interfaces on the device. While helpful for a quick status check, it lacks detail and real-time tracking, making it unsuitable for deep troubleshooting of a specific interface experiencing packet loss.

• monitor interface traffic (D) is not a recognized command for standard Juniper interface monitoring. It does not provide the necessary detailed or real-time error statistics.

Therefore, the best command for diagnosing packet loss with live updates on interface ge-0/0/3 is monitor interface ge-0/0/3. It offers continuous monitoring of errors and traffic, enabling effective identification and troubleshooting of packet loss problems as they occur.

Question 5:

Which command-line prompt indicates that you are currently in configuration mode on a network device?

A. >
B. $
C. #
D. %

Correct Answer: C

Explanation:

When working with Cisco networking devices like routers or switches, the command-line interface (CLI) prompt provides an important visual cue about the current mode of operation. Each prompt symbol corresponds to a different privilege level or mode, helping users understand what commands are available.

The # prompt specifically indicates that the device is in configuration mode. This mode is entered from the privileged EXEC mode and allows the user to make changes to the device’s configuration—such as modifying routing protocols, setting up interfaces, or applying security policies. For example, after typing configure terminal in privileged EXEC mode, the prompt changes from Router# to Router(config)#, signaling configuration mode.

To clarify the other options:

• A (>) represents the user EXEC mode, which offers limited access to commands primarily for viewing status and basic diagnostics. You cannot make configuration changes in this mode.

• B ($) is not a Cisco prompt. It is commonly seen in Unix-like operating systems such as Linux or macOS terminals, and is unrelated to Cisco device modes.

• D (%) is sometimes seen in Cisco devices as part of error or warning messages but does not signify any operational mode like configuration mode.

Understanding the prompt symbol is crucial because it indicates whether you can view information or make configuration changes. Seeing the # means you have the necessary privilege level to configure the device, making it a key indicator for network administrators. Therefore, C is the correct answer since the # prompt confirms that the device is in configuration mode.

Question 6:

Which two statements accurately describe the functions of a Routing Engine? (Choose two.)

A. It handles traffic marked with Class of Service (CoS).
B. It manages processing of control and management traffic.
C. It is responsible for maintaining and updating routing tables.
D. It forwards data packets through the network.

Correct Answers: B and C

Explanation:

The Routing Engine (RE) is a vital component within routers or similar network devices, responsible primarily for control-plane operations. Its duties focus on managing routing protocols, system management tasks, and maintaining the logical structure of the routing information.

First, B is correct because the Routing Engine processes management traffic. This includes handling administrative tasks such as configuration commands, SNMP queries, and other control-plane communications necessary for network device management. The RE ensures these management operations are performed accurately and efficiently, supporting overall device stability.

Second, C is also correct because maintaining and updating the routing tables is a core function of the Routing Engine. It receives routing updates from protocols like OSPF, BGP, or RIP, processes them to determine optimal paths, and stores this information in the routing table. This routing data guides the device in making forwarding decisions but the actual forwarding happens elsewhere.

The other options clarify what the Routing Engine does not do:

• A is incorrect because traffic marked with Class of Service (CoS) is typically handled by the Forwarding Engine (FE), which processes data-plane operations and prioritizes packets based on QoS policies. The RE does not manage packet forwarding or CoS marking directly.

• D is incorrect because forwarding transit traffic is the responsibility of the Forwarding Engine, not the Routing Engine. The RE focuses on control-plane functions and routing logic, while the FE handles high-speed data forwarding.

In summary, the Routing Engine manages management traffic and maintains routing tables (control-plane functions), whereas forwarding and CoS processing are delegated to the Forwarding Engine. Therefore, the correct answers are B and C.

Question 7:

Which two commands can be used to switch from operational mode to configuration mode in network devices like Juniper routers? (Select two.)

A. quit
B. configure
C. exit
D. edit

Correct Answer: B, D

Explanation:

In network devices running Junos OS, such as Juniper routers and switches, users work within two main modes: operational mode and configuration mode. Operational mode is primarily used for monitoring and troubleshooting, while configuration mode allows users to modify device settings. Switching between these modes is fundamental for managing the device effectively.

The two correct ways to enter configuration mode from operational mode are the configure and edit commands:

• The configure command (Option B) is the standard and most common method to transition from operational mode to configuration mode. Typing this command at the operational prompt initiates a switch to configuration mode, enabling the user to start making changes to the device’s settings.

• The edit command (Option D) also brings the user into configuration mode but allows more granularity. It lets users enter directly into a specific section or hierarchical level of the configuration tree. This command is useful when a user wants to work on a particular part of the configuration without starting at the root level, streamlining the editing process.

On the other hand, the other options are incorrect because they serve to exit or move out of modes rather than enter configuration mode:

• The quit command (Option A) is used to back out of sub-modes or return to a higher prompt level. It doesn’t initiate entry into configuration mode.

• The exit command (Option C) functions similarly to quit, allowing users to leave configuration or operational modes, not to enter configuration mode.

In summary, to move from operational mode to configuration mode in Junos devices, users should employ the configure or edit commands, making options B and D the correct choices.

Question 8:

Which statement accurately describes how exception traffic is handled in a router?

A. Exception traffic is discarded by the Packet Forwarding Engine (PFE).
B. Exception traffic is rate-limited to protect the Routing Engine (RE).
C. Exception traffic is always dropped when the router is congested.
D. Exception traffic is never forwarded anywhere.

Correct Answer: B

Explanation:

Exception traffic refers to packets that cannot be processed by the router’s high-speed hardware forwarding plane, the Packet Forwarding Engine (PFE). These packets require special treatment by the Routing Engine (RE), which performs software-based processing. This type of traffic often includes control packets, error messages, or packets that need deeper inspection beyond normal forwarding.

Reviewing each option clarifies how exception traffic is handled:

• Option A: The claim that exception traffic is discarded by the PFE is false. The PFE does not simply drop exception traffic; instead, it forwards it to the RE for software processing. Discarding such traffic without processing would disrupt essential router functions.

• Option B: This is the correct statement. Exception traffic is rate-limited to protect the RE. Since the RE operates at a slower processing speed than the PFE, flooding it with too much exception traffic could overwhelm it, degrading the router’s overall performance. Rate-limiting ensures that exception packets are delivered in manageable amounts so the RE can handle them effectively without being overloaded.

• Option C: The idea that exception traffic is always dropped during congestion is incorrect. While congestion may lead to packet drops, exception traffic is not automatically discarded. Routers apply policies and controls, and only drop traffic if necessary.

• Option D: Saying exception traffic is never forwarded is wrong because exception traffic must be forwarded to the RE for necessary processing. Without forwarding, important control functions and error handling could fail.

In conclusion, exception traffic is carefully managed by rate-limiting it to safeguard the RE, making Option B the accurate description.

Question 9:

Which keyboard shortcut in Junos OS moves the cursor to the beginning of the current command line?

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

Correct Answer: B

Explanation:

In Junos OS, as well as many Unix-like systems, command-line efficiency is enhanced by using keyboard shortcuts that help users quickly navigate and edit commands. One important shortcut allows you to jump directly to the start of the command line without having to use arrow keys repeatedly. This shortcut is Ctrl+a.

The Ctrl+a shortcut is widely recognized in command-line environments to reposition the cursor at the very beginning of the line. This function is particularly useful when you need to edit or review something at the start of a long command string quickly.

Now, let’s analyze why the other options are not correct:

• Ctrl+e (Option A) moves the cursor to the end of the command line. This is the opposite of Ctrl+a and is helpful when you want to jump to the line’s end to append or modify the command.

• Ctrl+k (Option C) deletes all characters from the current cursor position to the end of the line. This is a useful editing shortcut but does not move the cursor to the start.

• Ctrl+w (Option D) deletes the word immediately before the cursor. This shortcut assists in quick text editing by removing words but does not reposition the cursor to the beginning of the line.

Using keyboard shortcuts like Ctrl+a significantly increases efficiency in network device management by allowing quick cursor movement and reducing reliance on arrow keys. This reduces typing effort and accelerates the configuration or troubleshooting processes.

Therefore, Ctrl+a is the correct choice as it moves the cursor to the start of the line in Junos OS command-line interface.

Question 10:

Which two functions are performed by the Routing Engine (RE) in a router? (Select two.)

A. It does not handle routing updates.
B. It replies to ping and traceroute commands.
C. It manages and updates the routing tables.
D. It forwards transit traffic packets.

Correct Answer: B, C

Explanation:

The Routing Engine (RE) is a vital part of a router responsible for managing control-plane operations, including routing protocols, administrative tasks, and network diagnostics. To understand its roles, it’s important to examine each option carefully.

• Option A states that the RE does not process routing updates, which is incorrect. The RE is deeply involved in receiving, processing, and managing routing updates from dynamic routing protocols such as OSPF, BGP, or RIP. These updates allow the RE to learn about network topology changes and build accurate routing information.

• Option B is correct. The Routing Engine handles administrative and control functions, including responding to diagnostic commands like ping and traceroute. These commands test connectivity and network health, and the RE is responsible for generating and replying to these requests.

• Option C is also correct. The RE maintains the routing tables, which store the best paths to various network destinations based on routing protocols. Keeping these tables updated ensures that the router forwards packets efficiently using the most optimal routes.

• Option D is incorrect because forwarding transit traffic (the actual movement of data packets through the router) is not a function of the RE. Instead, this is the responsibility of the Packet Forwarding Engine (PFE), which operates at high speeds to handle large volumes of transit traffic.

In summary, the Routing Engine manages network control tasks such as processing routing updates, maintaining routing tables, and responding to network diagnostic commands, but it does not process the forwarding of transit data. Therefore, the correct answers are B and C.