Free JN0-106 Practice Test Questions | Know You're Ready for Junos - Associate (JNCIA-Junos) Junos OS 21.2

Explanation:
Junos route selection follows a specific order: longest prefix match first, then preference (lower is better), then other tie-breakers. For destination 10.50.10.55, the most specific match is 10.50.10.0/24 (24-bit prefix) versus 10.50.0.0/16 (16-bit) or default route (0/0). Longest prefix match overrides preference values.

Correct Option:

C: Route 10.50.10.0/24 will be selected using next hop 192.168.1.20 because it has the longest prefix match for the destination address.
10.50.10.55 falls within the 10.50.10.0/24 network. Although the exhibit shows two 10.50.10.0/24 routes (BGP/170 and OSPF/10), the OSPF route has lower preference (10 vs. 170), so it becomes active. However, the key point is the /24 prefix is chosen over less specific routes due to longest match.

Incorrect Option:

A: Route 0.0.0.0/0 will be selected using next hop 203.0.113.1 because the default route matches all destinations and has been active the longest.
The default route is the least specific (0-bit prefix). Longest prefix match is evaluated before default route. A more specific route (any /24, /16, or /8) will always be preferred over default regardless of age or preference.

B: Route 10.50.0.0/16 will be selected using next hop 192.168.1.10 because OSPF has a better preference value than BGP.
The /16 route is less specific than the /24 route. Longest prefix match takes priority over preference comparison. The existence of a /24 route supersedes the /16 route regardless of protocol preference

D: Route 10.0.0.0/8 will be selected using next hop 192.168.1.1 because it was learned from the static routing protocol which has the lowest preference value.
The /8 route is far less specific than the /16 or /24 routes. Longest prefix match rule ensures that a longer prefix (e.g., /24) is chosen before a shorter prefix (/8 or /0), even if the shorter prefix has a better preference (static preference 5).

Reference:
Juniper TechLibrary – "Routing Tables and Route Selection": Junos selects the active route by first performing the longest prefix match, then comparing route preference (lower is better), and finally tie-breakers such as next-hop or age.

Explanation:
Fiber-optic connectors are specialized interfaces designed for terminating optical fibers. LC (Lucent Connector) and SC (Subscriber Connector) are two common fiber connector types used in networking equipment, including Juniper devices, for Gigabit Ethernet and other optical interfaces.

Correct Option:

A: LC
LC (Lucent Connector) is a small form-factor fiber-optic connector with a 1.25 mm ferrule. It is widely used on SFP, SFP+, and QSFP transceivers due to its high density and push-pull latching mechanism.

C: SC
SC (Subscriber Connector or Standard Connector) is a square-shaped, push-pull fiber connector with a 2.5 mm ferrule. It is commonly found on older Gigabit Ethernet interfaces and GPON networks.

Incorrect Option:

B: RJ-45
RJ-45 is a copper twisted-pair connector used for Ethernet (Cat5, Cat6) and telephony. It is not a fiber-optic connector; it carries electrical signals over copper cables.

D: BNC
BNC (Bayonet Neill-Concelman) is a coaxial cable connector used for legacy 10BASE2 Ethernet, video, and RF applications. It is not designed for fiber optics.

Reference:
Juniper TechLibrary – "Fiber-Optic Connectors": Common fiber connector types include LC, SC, FC, ST, and MTP/MPO. LC and SC are frequently used on Juniper optical interfaces and transceivers.

Explanation:
Exception traffic in Junos refers to packets that cannot be processed entirely within the Packet Forwarding Engine (PFE) and must be sent to the Routing Engine (RE) for further handling. This includes packets destined to the RE itself (management traffic) and packets requiring special processing like IP options.

Correct Option:

A: An IP packet with the Router Alert option set in the IP options field.
IP packets with options (including Router Alert) cannot be fast-forwarded by the PFE and are treated as exception traffic. They are punted to the RE for processing, as the PFE cannot parse complex IP options at line rate.

B: SSH traffic to the local Junos OS device.
Any traffic destined to the device's own IP addresses (management traffic such as SSH, telnet, SNMP, or NETCONF) is exception traffic. The PFE forwards these packets to the RE because the RE is the ultimate destination.

Incorrect Option:

C: An IP packet that has the IP precedence CoS bits of 111 in the ToS field.
CoS bits (DSCP/IP Precedence) do not cause exception handling. The PFE can classify and forward such packets based on CoS settings without involving the RE, as long as the packet is transit traffic.

D: SSH traffic to a remote server on the Internet.
SSH traffic that transits the device (destined for a remote server) is normal transit traffic. It is processed by the PFE and forwarded out the appropriate interface without being sent to the RE.

Reference:
Juniper TechLibrary – "Exception Traffic": Exception traffic includes packets destined to the Routing Engine (e.g., management protocols) and packets requiring special processing such as IP options, fragmented packets, or TTL expiry.

Explanation:
Junos OS automatically stores committed configurations as rollback files (numbered 0 through 49 by default). Rollback 0 is the currently active configuration. The commit confirmed feature automatically rolls back to the previous configuration (rollback 1) if not confirmed within the specified timeout.

Correct Option:

A: Rollback configurations are applied automatically after a commit confirmed timeout.
When you issue commit confirmed, the device commits the changes and starts a timer. If you do not issue commit before the timer expires, Junos automatically performs a rollback 1 followed by commit, reverting to the previous active configuration.

C: Rollback files are stored automatically after each commit.
Every successful commit automatically saves the newly committed configuration as a rollback file. The previous rollback files shift (e.g., rollback 0 becomes rollback 1, rollback 1 becomes rollback 2, etc.). This provides a history of configuration changes.

Incorrect Option:

B: Rollback 0 always refers to the factory default configuration.
Rollback 0 refers to the currently active (committed) configuration, not factory defaults. Factory default configuration is typically rollback 0 only on a freshly zeroized device before any changes are made.

D: Up to 100 rollback configurations are maintained by default.
The default number of rollback files maintained is 50 (rollback 0 through rollback 49), not 100. This can be increased using set system max-configurations-on-flash up to 49 additional files.

Reference:
Juniper TechLibrary – "Configuration Rollback and Commit Confirmed": Junos stores up to 50 rollback files by default. commit confirmed automatically reverts to the previous configuration if not confirmed. Each successful commit generates a new rollback file.

Explanation:
In Junos OS, the out-of-band management interface is typically fxp0 (on older platforms) or em0 (on newer platforms like vMX or certain appliances). To isolate management traffic from the default inet.0 routing table, you enable the management instance using set system management-instance, which places the management interface into a dedicated routing instance called mgmt_junos.

Correct Option:

D: Assign an IP address to interface fxp0.0 or em0.0 and use the command set system management-instance to enable the management routing instance.
The management-instance feature automatically moves fxp0 or em0 into a separate routing instance (mgmt_junos). This isolates all management traffic (SSH, SNMP, NTP, syslog) from transit traffic in inet.0, improving security and avoiding routing conflicts.

Incorrect Option:

A: Configure an IP address on interface ge-0/0/0.0 and enable ethernet-switching family.
ge-0/0/0 is typically a data-plane interface, not out-of-band management. Enabling ethernet-switching is for Layer 2 switching, not for isolating management traffic into a separate routing instance.

B: Configure the lo0.0 loopback interface with a management IP and apply it to the [edit system services] hierarchy.
lo0.0 is a loopback interface used for router IDs and stable management addresses, but it does not provide out-of-band isolation. Applying it under system services is not a valid method for creating a separate management routing instance.

C: Assign an IP address to the me0.0 interface and set the routing-options to instance-type virtual-router.
me0.0 is the management Ethernet interface on some Juniper platforms (e.g., MX series). However, setting instance-type virtual-router under routing-options is incorrect syntax; the management instance is enabled via set system management-instance, not by manually defining a virtual-router.

Reference:
Juniper TechLibrary – "Configuring the Management Instance": Use set system management-instance to isolate management traffic on fxp0 or em0 into a dedicated routing instance called mgmt_junos. Management and transit traffic remain separate.

Explanation:
The monitor interface command in Junos provides real-time, continuously updating statistics for a specified interface. It displays live traffic rates (input/output bps, pps, and utilization) at a configurable interval, making it ideal for identifying intermittent slowness or over-utilization as it happens.

Correct Option:

B: monitor interface ge-0/0/5
This command refreshes interface statistics at a default interval of every 10 seconds. It shows live ingress/egress bandwidth usage, packet rates, and errors, allowing you to observe traffic spikes or sustained high utilization that could cause slowness.

Incorrect Option:

A: show chassis hardware
This command displays hardware inventory including FPCs, PICs, and interface modules. It provides no traffic statistics or real-time monitoring; it only shows physical components and their serial numbers.

C: show interfaces terse
This command provides a summarized, static view of all interfaces (or a specific one) showing operational status, protocol status, and configured IP addresses. It does not offer real-time traffic rates or continuous updates.

D: show interfaces ge-0/0/5 extensive
This command displays detailed static statistics (since last counter reset) including input/output rates averaged over a longer period. While useful for historical analysis, it does not provide live, refreshing updates like monitor interface.

Reference:
Juniper TechLibrary – "Monitoring Interface Traffic": The monitor interface command provides a dynamically updating display of interface traffic statistics, including current bandwidth utilization, to help troubleshoot performance issues in real time.

Explanation:
Configuration groups in Junos allow you to define a set of configuration statements once and apply them to multiple hierarchy levels using the apply-groups statement. This reduces repetitive commands, ensures consistency across interfaces, and simplifies future changes by updating only the group definition.

Correct Option:

C: Use a configuration group.
Create a group (e.g., groups interface-defaults) with common interface settings (description, MTU). Then apply this group to each interface using set interfaces ge-0/0/x apply-groups interface-defaults. Changes to the group automatically affect all interfaces using it.

Incorrect Option:

A: Use the wildcard delete command to remove duplicate settings.
wildcard delete is used to remove multiple similar configuration statements, not to apply consistent settings. It does not help in initially configuring interfaces uniformly.

B: Configure each interface individually.
While possible, this approach is repetitive, error-prone, and time-consuming for 20 interfaces. It does not leverage Junos automation features and makes bulk updates difficult.

D: Use search and replace to apply settings across interfaces.
Junos CLI does not have a native search-and-replace command for applying settings across multiple interfaces. You would need to manually edit the configuration or use scripts, which is less efficient than configuration groups.

Reference:
Juniper TechLibrary – "Configuration Groups": Configuration groups allow you to create reusable blocks of configuration that can be applied to multiple hierarchy levels, reducing redundancy and ensuring consistent settings across interfaces, protocols, or other elements.

Explanation:
Class of Service (CoS) in networking manages bandwidth allocation and traffic prioritization. During network congestion, CoS identifies critical traffic (e.g., voice, video) and gives it preferential treatment over less sensitive traffic (e.g., email, file transfers), ensuring quality of service for important applications.

Correct Option:

B: CoS prioritizes certain types of traffic during congestion.
This is the core function of CoS. Using classification, queuing, and scheduling mechanisms, CoS ensures that high-priority traffic (like real-time voice) is forwarded before low-priority traffic (like web browsing) when link congestion occurs.

Incorrect Option:

A: CoS encrypts traffic to secure data across the network.
Encryption is a security function handled by protocols like IPsec, SSL/TLS, or MACsec. CoS does not provide encryption; it only deals with traffic prioritization and bandwidth management.

C: CoS assigns IP addresses dynamically to optimize routing.
Dynamic IP address assignment is performed by DHCP (Dynamic Host Configuration Protocol), not by CoS. CoS operates on already-assigned IP packets and does not affect addressing.

D: CoS prevents broadcast storms by segmenting VLANs.
Broadcast storm prevention is achieved through VLAN segmentation, spanning-tree protocols, or storm control features. CoS does not segment VLANs or prevent broadcast storms; it prioritizes traffic within existing network segments.

Reference:
Juniper TechLibrary – "Class of Service Overview": CoS provides mechanisms to prioritize certain types of traffic when network congestion occurs, ensuring that critical applications receive the required bandwidth and latency treatment.