Practice Free JN0-106 Exam Online Questions
Question #1
Which IPv4 address and subnet mask combination represents a point-to-point link with only two usable host addresses?
- A . 192.168.1.0/30
- B . 192.168.1.0/29
- C . 192.168.1.0/24
- D . 192.168.1.0/28
Correct Answer: A
A
Explanation:
In networking architecture, point-to-point (P2P) links are used to interconnect two Layer 3 devices, such as a pair of Juniper MX series routers. Because these links only involve two endpoints, using a large subnet mask would result in wasted IP addresses. The standard historical prefix for a P2P link that provides exactly two usable host addresses is /30.
A /30 subnet mask (255.255.255.252) reserves 2 bits for the host portion. Applying the usable host formula ($2^2 – 2$) results in 2 usable addresses.
In the case of 192.168.1.0/30:
A
Explanation:
In networking architecture, point-to-point (P2P) links are used to interconnect two Layer 3 devices, such as a pair of Juniper MX series routers. Because these links only involve two endpoints, using a large subnet mask would result in wasted IP addresses. The standard historical prefix for a P2P link that provides exactly two usable host addresses is /30.
A /30 subnet mask (255.255.255.252) reserves 2 bits for the host portion. Applying the usable host formula ($2^2 – 2$) results in 2 usable addresses.
In the case of 192.168.1.0/30:
Question #2
Which routing table is used for IPv6 unicast routes by default?
- A . inet.0
- B . inet.6
- C . inet.1
- D . inet6.0
Correct Answer: D
D
Explanation:
In Junos OS, routing information is meticulously organized into separate databases known as routing tables, each identified by a specific name corresponding to an address family and its intended operational purpose. The master routing table for IPv4 unicast information is inet.0. For the IPv6 address family, Junos OS utilizes inet6.0 as the default master routing table for all unicast reachability information. This table stores all IPv6 prefixes learned from directly connected interfaces, static configurations, and dynamic routing protocols such as OSPFv3, IS-IS, or BGP.
It is a core architectural principle in Junos to isolate these families to ensure management clarity and prevent address space collisions. While the system utilizes other specialized tables for specific functions―such as inet.3 for MPLS path information or inet.1 for multicast forwarding caches―inet6.0 remains the primary repository for IPv6-based forwarding decisions. When a Junos device receives an IPv6 packet, the Packet Forwarding Engine (PFE) performs a lookup against the entries derived from this table to determine the appropriate egress interface and next-hop address. Understanding this default table structure is essential for network architects when troubleshooting dual-stack environments or configuring protocol-specific import and export policies.
D
Explanation:
In Junos OS, routing information is meticulously organized into separate databases known as routing tables, each identified by a specific name corresponding to an address family and its intended operational purpose. The master routing table for IPv4 unicast information is inet.0. For the IPv6 address family, Junos OS utilizes inet6.0 as the default master routing table for all unicast reachability information. This table stores all IPv6 prefixes learned from directly connected interfaces, static configurations, and dynamic routing protocols such as OSPFv3, IS-IS, or BGP.
It is a core architectural principle in Junos to isolate these families to ensure management clarity and prevent address space collisions. While the system utilizes other specialized tables for specific functions―such as inet.3 for MPLS path information or inet.1 for multicast forwarding caches―inet6.0 remains the primary repository for IPv6-based forwarding decisions. When a Junos device receives an IPv6 packet, the Packet Forwarding Engine (PFE) performs a lookup against the entries derived from this table to determine the appropriate egress interface and next-hop address. Understanding this default table structure is essential for network architects when troubleshooting dual-stack environments or configuring protocol-specific import and export policies.
Question #3
Which two statements are correct regarding Layer 2 network switches? (Choose two.)
- A . Switches are susceptible to traffic loops.
- B . Switches flood broadcast traffic.
- C . Switches do not learn MAC addresses.
- D . Switches create a single collision domain.
Correct Answer: A, B
A, B
Explanation:
In the Junos OS architecture and general networking standards, Layer 2 switches are designed to increase network efficiency by segmenting collision domains. Unlike legacy hubs, a switch creates a separate collision domain for each of its physical ports. This micro-segmentation allows for full-duplex communication, effectively eliminating the possibility of collisions on individual links. However, while switches segment collision domains, they maintain a single broadcast domain by default.
When a switch receives a broadcast frame, such as an ARP request, it must ensure the frame reaches all possible destinations within the local segment. Consequently, the switch floods the broadcast traffic out of all ports except the one on which it was received. This flooding behavior, while necessary for protocol discovery, makes Layer 2 networks susceptible to traffic loops. If redundant physical paths exist between switches without a loop-prevention mechanism like the Spanning Tree Protocol (STP), broadcast frames can circulate endlessly, leading to a broadcast storm that consumes all available bandwidth and processor resources on the Routing Engine. Furthermore, switches are highly active learners; they populate their Media Access Control (MAC) tables by observing the source addresses of incoming frames to ensure that subsequent unicast traffic is precisely forwarded rather than flooded. Therefore, understanding the management of broadcast domains and the risks of loops is a core competency for any Junos Associate.
A, B
Explanation:
In the Junos OS architecture and general networking standards, Layer 2 switches are designed to increase network efficiency by segmenting collision domains. Unlike legacy hubs, a switch creates a separate collision domain for each of its physical ports. This micro-segmentation allows for full-duplex communication, effectively eliminating the possibility of collisions on individual links. However, while switches segment collision domains, they maintain a single broadcast domain by default.
When a switch receives a broadcast frame, such as an ARP request, it must ensure the frame reaches all possible destinations within the local segment. Consequently, the switch floods the broadcast traffic out of all ports except the one on which it was received. This flooding behavior, while necessary for protocol discovery, makes Layer 2 networks susceptible to traffic loops. If redundant physical paths exist between switches without a loop-prevention mechanism like the Spanning Tree Protocol (STP), broadcast frames can circulate endlessly, leading to a broadcast storm that consumes all available bandwidth and processor resources on the Routing Engine. Furthermore, switches are highly active learners; they populate their Media Access Control (MAC) tables by observing the source addresses of incoming frames to ensure that subsequent unicast traffic is precisely forwarded rather than flooded. Therefore, understanding the management of broadcast domains and the risks of loops is a core competency for any Junos Associate.
Question #4
Which command is used to view real-time traffic statistics for all interfaces?
- A . show interfaces extensive
- B . monitor interface traffic
- C . monitor traffic interface all
- D . show interfaces statistics
Correct Answer: B
B
Explanation:
In Junos OS, there is a distinct difference between show commands and monitor commands. While show commands provide a static snapshot of the current state of the device or its interfaces at the moment the command is executed, monitor commands provide dynamic, real-time updates. To view live traffic statistics across all physical and logical interfaces, the correct command is monitor interface traffic.
When this command is executed, the CLI enters an interactive text-based interface (TUI) that displays a list of interfaces along with their input and output rates in bits per second (bps) and packets per second (pps). The display refreshes automatically (usually every few seconds), allowing an administrator to observe traffic spikes or drops as they occur without manually re-running a command. This is an invaluable tool for troubleshooting congestion or verifying that traffic is flowing as expected after a configuration change. Commands like show interfaces extensive provide significantly more detail―including error counters and physical layer parameters―but they are not real-time and require manual execution to update the statistics. The monitor interface traffic command simplifies the view to focus specifically on throughput metrics across the entire device. Operational Monitoring and Maintenance, Interface Monitoring, Real-time Statistics.
B
Explanation:
In Junos OS, there is a distinct difference between show commands and monitor commands. While show commands provide a static snapshot of the current state of the device or its interfaces at the moment the command is executed, monitor commands provide dynamic, real-time updates. To view live traffic statistics across all physical and logical interfaces, the correct command is monitor interface traffic.
When this command is executed, the CLI enters an interactive text-based interface (TUI) that displays a list of interfaces along with their input and output rates in bits per second (bps) and packets per second (pps). The display refreshes automatically (usually every few seconds), allowing an administrator to observe traffic spikes or drops as they occur without manually re-running a command. This is an invaluable tool for troubleshooting congestion or verifying that traffic is flowing as expected after a configuration change. Commands like show interfaces extensive provide significantly more detail―including error counters and physical layer parameters―but they are not real-time and require manual execution to update the statistics. The monitor interface traffic command simplifies the view to focus specifically on throughput metrics across the entire device. Operational Monitoring and Maintenance, Interface Monitoring, Real-time Statistics.
Question #5
Which two tasks are performed by the Routing Engine in a Junos device? (Choose two.)
- A . The Routing Engine runs routing protocols.
- B . The Routing Engine evaluates transit traffic against firewall filters.
- C . The Routing Engine manages the device configuration.
- D . The Routing Engine forwards transit traffic.
Correct Answer: A, C
A, C
Explanation:
The Routing Engine (RE) functions as the centralized processor and administrative core of any Junos OS-based platform. Its primary responsibility involves the execution and maintenance of the control plane, which includes running all active routing protocols such as OSPF, BGP, and IS-IS. Through these protocols, the RE exchanges topology information with neighboring routers, builds the Routing Information Base (RIB), and calculates the optimal paths for traffic. Once these paths are determined, the RE distributes the resulting Forwarding Information Base (FIB) to the Packet Forwarding Engine (PFE) for hardware-level execution.
In addition to its protocol duties, the Routing Engine manages the device configuration and the overall system environment. This includes providing the user interface (CLI or J-Web), managing the candidate and active configuration databases, and handling the commit process. While the PFE is specifically designed to forward transit traffic and evaluate that traffic against firewall filters at line rate, the RE focuses on the higher-level logic and management tasks. This architectural separation ensures that management functions―such as a complex configuration commit or a protocol re-convergence event―do not degrade the performance of the data plane, allowing the device to continue forwarding user traffic without interruption. Junos OS Fundamentals, Routing Engine Functions, Management and Control Planes.
A, C
Explanation:
The Routing Engine (RE) functions as the centralized processor and administrative core of any Junos OS-based platform. Its primary responsibility involves the execution and maintenance of the control plane, which includes running all active routing protocols such as OSPF, BGP, and IS-IS. Through these protocols, the RE exchanges topology information with neighboring routers, builds the Routing Information Base (RIB), and calculates the optimal paths for traffic. Once these paths are determined, the RE distributes the resulting Forwarding Information Base (FIB) to the Packet Forwarding Engine (PFE) for hardware-level execution.
In addition to its protocol duties, the Routing Engine manages the device configuration and the overall system environment. This includes providing the user interface (CLI or J-Web), managing the candidate and active configuration databases, and handling the commit process. While the PFE is specifically designed to forward transit traffic and evaluate that traffic against firewall filters at line rate, the RE focuses on the higher-level logic and management tasks. This architectural separation ensures that management functions―such as a complex configuration commit or a protocol re-convergence event―do not degrade the performance of the data plane, allowing the device to continue forwarding user traffic without interruption. Junos OS Fundamentals, Routing Engine Functions, Management and Control Planes.
Question #6
You are creating a new user account using a predefined login class on a Junos device. The account should be able to run operational mode commands such as show interfaces and ping, but should not be allowed to change or commit configuration.
Which login class should you assign to this user?
- A . maintenance
- B . read-only
- C . super-user
- D . operator
Correct Answer: D
D
Explanation:
Junos OS utilizes a Role-Based Access Control (RBAC) model through the use of login classes, which define the specific permissions and restrictions for different user levels. To simplify administration, Juniper provides several predefined classes that cater to common organizational roles. The requirement here is for an account that can perform basic network diagnostics (operational mode) but lacks the authority to modify the system state (configuration mode).
The operator class is specifically engineered for this purpose. It grants permissions such as clear, network, reset, trace, and view. These permissions allow the user to execute monitoring commands like show, use diagnostic tools like ping and traceroute, and clear statistics. Crucially, the operator class does not include the configure or commit permissions, preventing the user from entering configuration mode or making any permanent changes to the device.
Comparing this to other options: the read-only class is more restrictive, generally allowing only the viewing of configuration and some state data, but often restricting active diagnostic tools like ping. The super-user class provides unrestricted access, while maintenance is not a standard predefined class for general operational roles. Assigning the operator class ensures that junior staff or automated monitoring systems have the visibility they need to troubleshoot connectivity without risking the integrity of the device configuration.
D
Explanation:
Junos OS utilizes a Role-Based Access Control (RBAC) model through the use of login classes, which define the specific permissions and restrictions for different user levels. To simplify administration, Juniper provides several predefined classes that cater to common organizational roles. The requirement here is for an account that can perform basic network diagnostics (operational mode) but lacks the authority to modify the system state (configuration mode).
The operator class is specifically engineered for this purpose. It grants permissions such as clear, network, reset, trace, and view. These permissions allow the user to execute monitoring commands like show, use diagnostic tools like ping and traceroute, and clear statistics. Crucially, the operator class does not include the configure or commit permissions, preventing the user from entering configuration mode or making any permanent changes to the device.
Comparing this to other options: the read-only class is more restrictive, generally allowing only the viewing of configuration and some state data, but often restricting active diagnostic tools like ping. The super-user class provides unrestricted access, while maintenance is not a standard predefined class for general operational roles. Assigning the operator class ensures that junior staff or automated monitoring systems have the visibility they need to troubleshoot connectivity without risking the integrity of the device configuration.
Question #7
You are configuring a new router and want to ensure that you can recover from future misconfigurations.
In this scenario, what should you do after completing the initial configuration?
- A . Update the firmware on the router.
- B . Save the configuration as rollback 0.
- C . Create a rescue configuration.
- D . Enable automatic rollback after 10 minutes.
Correct Answer: C
C
Explanation:
In the Junos OS architecture, maintaining a reliable recovery point is a critical post-installation task. While the system automatically archives previous configurations as "rollback" files every time a commit is performed, these files are transient and can eventually be rotated out of the default 50-file history as new changes are made. To ensure a permanent and reliable recovery state, a Senior Architect should manually create a rescue configuration.
The rescue configuration is a specifically designated file used to restore a device to a known-working state if it becomes unreachable or the configuration becomes corrupted. Unlike standard rollbacks, the rescue configuration is only created or updated when an administrator explicitly issues the operational mode command request system configuration rescue save. This ensures that even if several subsequent commits flush the desired initial state from the standard rollback archive, the "safe harbor" configuration remains intact on the storage media. This state can then be re-activated via the rollback rescue command in configuration mode followed by a commit. Setting a rescue configuration after the initial setup is a foundational best practice for disaster recovery and operational stability, providing a "last resort" configuration that is immune to the automated rotation of the commit history.
C
Explanation:
In the Junos OS architecture, maintaining a reliable recovery point is a critical post-installation task. While the system automatically archives previous configurations as "rollback" files every time a commit is performed, these files are transient and can eventually be rotated out of the default 50-file history as new changes are made. To ensure a permanent and reliable recovery state, a Senior Architect should manually create a rescue configuration.
The rescue configuration is a specifically designated file used to restore a device to a known-working state if it becomes unreachable or the configuration becomes corrupted. Unlike standard rollbacks, the rescue configuration is only created or updated when an administrator explicitly issues the operational mode command request system configuration rescue save. This ensures that even if several subsequent commits flush the desired initial state from the standard rollback archive, the "safe harbor" configuration remains intact on the storage media. This state can then be re-activated via the rollback rescue command in configuration mode followed by a commit. Setting a rescue configuration after the initial setup is a foundational best practice for disaster recovery and operational stability, providing a "last resort" configuration that is immune to the automated rotation of the commit history.
Question #8
Which two traffic types are processed by a Routing Engine using Junos OS? (Choose two.)
- A . traffic with CoS markings
- B . transit traffic
- C . routing updates
- D . local management traffic
Correct Answer: C, D
C, D
Explanation:
The Routing Engine (RE) in a Junos device serves as the centralized intelligence and management hub, primarily responsible for the control and management planes of the system. In this capacity, the RE is tasked with processing routing updates, such as OSPF Link State Advertisements (LSAs) or BGP Update messages. These updates are vital for the RE to maintain the Routing Information Base (RIB), calculate the shortest paths, and subsequently populate the Forwarding Information Base (FIB) which is then pushed to the Packet Forwarding Engine (PFE).
Furthermore, the Routing Engine handles all local management traffic. This category encompasses administrative access through the Command Line Interface (CLI) via SSH or Telnet, SNMP queries from network management systems, and system logging processes. Because the RE runs the Junos OS kernel, it must directly interpret and respond to these management-level requests to ensure the device remains configurable and observable. Conversely, transit traffic―the data passing through the device from one ingress port to an egress port―is offloaded to the PFE to be handled at wire speed. While the PFE manages the heavy lifting of data forwarding and Class of Service (CoS) application, the RE remains focused on high-level protocol maintenance and system administration, ensuring that control plane stability is maintained even under heavy traffic loads. Junos OS Fundamentals, Control Plane Functions, Routing Engine Traffic.
C, D
Explanation:
The Routing Engine (RE) in a Junos device serves as the centralized intelligence and management hub, primarily responsible for the control and management planes of the system. In this capacity, the RE is tasked with processing routing updates, such as OSPF Link State Advertisements (LSAs) or BGP Update messages. These updates are vital for the RE to maintain the Routing Information Base (RIB), calculate the shortest paths, and subsequently populate the Forwarding Information Base (FIB) which is then pushed to the Packet Forwarding Engine (PFE).
Furthermore, the Routing Engine handles all local management traffic. This category encompasses administrative access through the Command Line Interface (CLI) via SSH or Telnet, SNMP queries from network management systems, and system logging processes. Because the RE runs the Junos OS kernel, it must directly interpret and respond to these management-level requests to ensure the device remains configurable and observable. Conversely, transit traffic―the data passing through the device from one ingress port to an egress port―is offloaded to the PFE to be handled at wire speed. While the PFE manages the heavy lifting of data forwarding and Class of Service (CoS) application, the RE remains focused on high-level protocol maintenance and system administration, ensuring that control plane stability is maintained even under heavy traffic loads. Junos OS Fundamentals, Control Plane Functions, Routing Engine Traffic.
Question #9
You are asked to subnet the broadcast domains but need to support 50 hosts. In this scenario, which subnet mask would satisfy this requirement?
- A . /26
- B . /27
- C . /28
- D . /29
Correct Answer: A
A
Explanation:
Determining the appropriate subnet mask for a specific host requirement is a core task in designing Junos-based network infrastructures. The number of usable hosts in an IPv4 subnet is calculated using the formula $2^n – 2$, where $n$ represents the number of host bits remaining after the network prefix. In this scenario, the requirement is to support 50 hosts within a single broadcast domain.
Evaluating the options:
A /29 mask provides 3 host bits ($2^3 – 2 = 6$ hosts), which is insufficient.
A /28 mask provides 4 host bits ($2^4 – 2 = 14$ hosts), which is insufficient.
A /27 mask provides 5 host bits ($2^5 – 2 = 30$ hosts), which still fails to meet the 50-host threshold.
A /26 mask provides 6 host bits. Applying the formula: $2^6 – 2 = 64 – 2 = 62$ usable host addresses.
Since a /26 mask provides 62 usable addresses, it is the smallest standard subnet mask that fully satisfies the requirement of 50 hosts. Using a /26 mask allows for the 50 required hosts while providing a small buffer for future growth (12 additional addresses) without wasting the excessive address space associated with a /25 or /24 mask. This efficient allocation of address space is a best practice for maintaining scalable and organized routing tables on Juniper devices.
A
Explanation:
Determining the appropriate subnet mask for a specific host requirement is a core task in designing Junos-based network infrastructures. The number of usable hosts in an IPv4 subnet is calculated using the formula $2^n – 2$, where $n$ represents the number of host bits remaining after the network prefix. In this scenario, the requirement is to support 50 hosts within a single broadcast domain.
Evaluating the options:
A /29 mask provides 3 host bits ($2^3 – 2 = 6$ hosts), which is insufficient.
A /28 mask provides 4 host bits ($2^4 – 2 = 14$ hosts), which is insufficient.
A /27 mask provides 5 host bits ($2^5 – 2 = 30$ hosts), which still fails to meet the 50-host threshold.
A /26 mask provides 6 host bits. Applying the formula: $2^6 – 2 = 64 – 2 = 62$ usable host addresses.
Since a /26 mask provides 62 usable addresses, it is the smallest standard subnet mask that fully satisfies the requirement of 50 hosts. Using a /26 mask allows for the 50 required hosts while providing a small buffer for future growth (12 additional addresses) without wasting the excessive address space associated with a /25 or /24 mask. This efficient allocation of address space is a best practice for maintaining scalable and organized routing tables on Juniper devices.
Question #9
You are asked to subnet the broadcast domains but need to support 50 hosts. In this scenario, which subnet mask would satisfy this requirement?
- A . /26
- B . /27
- C . /28
- D . /29
Correct Answer: A
A
Explanation:
Determining the appropriate subnet mask for a specific host requirement is a core task in designing Junos-based network infrastructures. The number of usable hosts in an IPv4 subnet is calculated using the formula $2^n – 2$, where $n$ represents the number of host bits remaining after the network prefix. In this scenario, the requirement is to support 50 hosts within a single broadcast domain.
Evaluating the options:
A /29 mask provides 3 host bits ($2^3 – 2 = 6$ hosts), which is insufficient.
A /28 mask provides 4 host bits ($2^4 – 2 = 14$ hosts), which is insufficient.
A /27 mask provides 5 host bits ($2^5 – 2 = 30$ hosts), which still fails to meet the 50-host threshold.
A /26 mask provides 6 host bits. Applying the formula: $2^6 – 2 = 64 – 2 = 62$ usable host addresses.
Since a /26 mask provides 62 usable addresses, it is the smallest standard subnet mask that fully satisfies the requirement of 50 hosts. Using a /26 mask allows for the 50 required hosts while providing a small buffer for future growth (12 additional addresses) without wasting the excessive address space associated with a /25 or /24 mask. This efficient allocation of address space is a best practice for maintaining scalable and organized routing tables on Juniper devices.
A
Explanation:
Determining the appropriate subnet mask for a specific host requirement is a core task in designing Junos-based network infrastructures. The number of usable hosts in an IPv4 subnet is calculated using the formula $2^n – 2$, where $n$ represents the number of host bits remaining after the network prefix. In this scenario, the requirement is to support 50 hosts within a single broadcast domain.
Evaluating the options:
A /29 mask provides 3 host bits ($2^3 – 2 = 6$ hosts), which is insufficient.
A /28 mask provides 4 host bits ($2^4 – 2 = 14$ hosts), which is insufficient.
A /27 mask provides 5 host bits ($2^5 – 2 = 30$ hosts), which still fails to meet the 50-host threshold.
A /26 mask provides 6 host bits. Applying the formula: $2^6 – 2 = 64 – 2 = 62$ usable host addresses.
Since a /26 mask provides 62 usable addresses, it is the smallest standard subnet mask that fully satisfies the requirement of 50 hosts. Using a /26 mask allows for the 50 required hosts while providing a small buffer for future growth (12 additional addresses) without wasting the excessive address space associated with a /25 or /24 mask. This efficient allocation of address space is a best practice for maintaining scalable and organized routing tables on Juniper devices.