JN0-106 Practice Test 12 — 15 Questions

Question 1

Which command displays the status of all configured interfaces, including administrative and operational status?

Accepted Answer

show interfaces terse. The 'show interfaces terse' command displays a concise summary of all interfaces, including their administrative status (up or down) and operational status (up or down), along with protocol states. This makes it the correct choice for quickly viewing the status of all configured interfaces in a single output.

Answer

show configuration interfaces

Answer

show chassis hardware

Answer

show interface statistics

Question 2

A technician notices that the /var partition on a Junos device is 95% full. Which action will immediately free up disk space without affecting device operation?

Accepted Answer

Clear log files using 'clear log messages'. The 'clear log messages' command immediately removes the contents of the active log files (e.g., messages, interactive-commands) without requiring a reboot or affecting running processes. This directly frees up space in /var/log, which is a primary consumer of the /var partition, while leaving the directory structure intact so logging continues normally.

Answer

Delete unused software packages using 'request system software delete'

Answer

Reboot the device

Answer

Remove the /var/log directory

Question 3

A network administrator notices that traffic between two VLANs is not reaching its destination. The switch has an IRB interface configured with an IP address in each VLAN's subnet. What is the most likely missing configuration?

Accepted Answer

The VLANs are not defined on the switch.. The IRB interface provides Layer 3 routing between VLANs, but it requires the VLANs themselves to be defined on the switch. If the VLANs are not defined, the switch cannot associate the IRB interface with the correct broadcast domains, and traffic will not be forwarded between them. Option C correctly identifies this missing configuration.

Answer

The IRB interface does not have an IP address configured.

Answer

The VLANs are on different switches.

Answer

The switch ports are not configured for VLAN tagging.

Question 4

A network administrator is configuring a new interface and wants to ensure that the interface is enabled and can pass traffic. Which configuration element is required?

Accepted Answer

set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24. In Junos, an interface is administratively enabled by default (no explicit 'enable' command is needed), but to pass traffic it requires a logical unit with a configured protocol family and an IP address. The command 'set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24' creates unit 0, assigns the IPv4 address, and implicitly enables the interface for traffic forwarding. Without an address under a family, the interface cannot pass IP traffic even if it is administratively up.

Answer

set interfaces ge-0/0/0 enable

Answer

set interfaces ge-0/0/0 unit 0 family inet

Answer

set interfaces ge-0/0/0 disable

Question 5

What happens when a user issues the 'request system reboot' command without any options?

Accepted Answer

The device prompts for confirmation.. When a user issues the 'request system reboot' command without any options, Junos OS prompts for confirmation before proceeding. This is a safety mechanism to prevent accidental reboots, as the command does not automatically reboot the device immediately or schedule a delayed reboot by default.

Answer

The device reboots after the current commit.

Answer

The device reboots immediately.

Answer

The device schedules a reboot in 5 minutes.

Question 6

Refer to the exhibit. A security analyst sees repeated login failures from 10.0.0.2 for user1. Which Junos feature can be used to automatically block further login attempts from that IP?

Accepted Answer

Apply a firewall filter to the loopback interface that polices SSH traffic.. Applying a firewall filter to the loopback interface (lo0) that polices SSH traffic can automatically block further login attempts from a specific IP address, such as 10.0.0.2. The loopback interface is the termination point for all control-plane traffic on a Junos device, including SSH sessions. By configuring a firewall filter with a policer that limits the rate of SSH packets from a source IP, excessive login failures can trigger the policer to drop subsequent packets, effectively blocking the attacker without manual intervention.

Answer

Configure SSH to accept only public key authentication for user1.

Answer

Disable the user1 account.

Answer

Set the 'session-limit' for user1 to prevent multiple login attempts.

Question 7

A network administrator notices that the CPU utilization on an MX240 router has been consistently above 90% for the past hour. Users are reporting intermittent connectivity issues. The administrator logs in and runs 'show system processes extensive' which shows the Routing Protocol Daemon (rpd) consuming 70% of the CPU. Further investigation reveals that the router has over 5000 BGP prefixes from multiple peers. The administrator suspects that the high CPU is due to continuous route processing. What should the administrator do to immediately reduce CPU load while maintaining network stability?

Accepted Answer

Apply a prefix-limit on each BGP session to restrict the number of prefixes received. Applying a prefix-limit on each BGP session immediately restricts the number of prefixes the router will accept from peers. This prevents the Routing Protocol Daemon (rpd) from processing excessive BGP updates, reducing CPU load while maintaining network stability by keeping existing sessions and routes intact. The prefix-limit action (e.g., with a teardown threshold) ensures the router does not accept more prefixes than it can handle, directly addressing the root cause of high CPU usage.

Answer

Perform a 'show log messages' to check for errors before taking action

Answer

Bounce all BGP sessions by clearing them with 'clear bgp neighbor *'

Answer

Disable BGP multipath to reduce route processing

Question 8

An administrator notices that after committing a configuration change on a Juniper MX router, the device loses connectivity to the management network. The management interface is part of a dedicated management routing instance. Which of the following is the most likely cause?

Accepted Answer

The routing instance for the management interface was accidentally removed. The management interface is part of a dedicated management routing instance (often named mgmt_junos). If this routing instance is accidentally removed during a commit, the management interface loses its routing context and becomes unreachable, causing loss of connectivity to the management network. This is a common misconfiguration when an administrator modifies routing instance configurations without realizing the management interface depends on it.

Answer

A firewall filter was applied to the management interface that blocks all traffic

Answer

NTP was configured with an incorrect server address

Answer

A syslog server was configured that is unreachable

Question 9

Refer to the exhibit. Why is the route for 192.168.1.0/24 hidden?

Accepted Answer

The next-hop is unreachable. A route is hidden in the JUNOS routing table when its next-hop is unreachable. The show route command displays only active routes; if the next-hop address is not reachable via any active interface or route, the route is suppressed (hidden) and not used for forwarding. This is a fundamental behavior of JUNOS route selection and differs from Cisco IOS, which may still display such routes.

Answer

The route has a higher metric

Answer

The route has a lower preference

Answer

The route is not committed

Question 10

Which two events typically trigger a change to the routing table? (Choose two.)

Accepted Answer

Interface state change. An interface state change (up/down) directly affects the reachability of directly connected networks. When an interface goes up, Junos adds the corresponding directly connected route to the routing table; when it goes down, the route is removed. Similarly, a BGP neighbor reset causes the BGP session to be torn down and re-established, which triggers the withdrawal and re-advertisement of all BGP routes, thereby modifying the routing table.

Answer

System uptime

Answer

Log file rotation

Answer

Configuration commit

Question 11

Which Junos CLI mode allows a user to view the configuration and execute operational commands, but not make configuration changes?

Accepted Answer

Operational mode. In Junos OS, Operational mode (indicated by the `>` prompt) allows users to execute operational commands (e.g., `show`, `ping`, `traceroute`) and view the active configuration using `show configuration`, but it does not permit any changes to the configuration. Configuration changes require entering Configuration mode (indicated by the `#` prompt) via the `configure` command. This separation enforces a strict two-tier access model, ensuring that operational tasks do not inadvertently alter the device's configuration.

Answer

Monitor mode

Answer

Enable mode

Answer

Configuration mode

Question 12

You are a network engineer responsible for a Juniper MX240 router in a data center. The router is running Junos 18.2R1 and you need to upgrade it to 19.1R2 to fix a critical security vulnerability. You establish an SSH session to the router and enter configuration mode to prepare the upgrade. While in configuration mode, you notice that the candidate configuration contains several uncommitted changes from a previous engineer that attempted to modify BGP settings but introduced a syntax error. The candidate configuration fails any commit operation due to this error. The currently active configuration is stable and the router is handling production traffic. The upgrade process requires you to change the boot media and specify the new image. Which action should you take to clear the candidate configuration and proceed with the upgrade?

Accepted Answer

Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands.. The 'rollback 0' command discards all uncommitted changes in the candidate configuration and replaces it with the active, committed configuration. This clears the syntax error without affecting the running router, allowing you to proceed with the upgrade commands (e.g., 'request system software add') without a reboot or forced commit.

Answer

Reboot the router to clear the candidate configuration and then start the upgrade.

Answer

Run the 'load override terminal' command and paste the active configuration from memory, then commit and upgrade.

Answer

Use the 'commit force' command to override the syntax error and commit the candidate, then perform the upgrade.

Question 13

Based on the exhibit, what is the most likely impact on the router?

Accepted Answer

Routing protocol adjacencies will be lost, causing routing instability.. The exhibit shows kernel messages indicating a hardware or software fault (e.g., a FPC crash or PIC restart). In Junos, such critical events cause the Packet Forwarding Engine (PFE) to reset, which tears down all routing protocol adjacencies (OSPF, BGP, IS-IS) because the control plane loses communication with the forwarding plane. This leads to route withdrawal and routing instability until the adjacencies are re-established.

Answer

The CPU will be overloaded due to the kernel messages.

Answer

The router will stop forwarding packets immediately.

Answer

The router will reboot automatically.

Question 14

A network administrator is troubleshooting a missing route in the routing table. The route is learned via OSPF, and the OSPF neighbor adjacency is up. Which command would help determine if OSPF received the route?

Accepted Answer

show ospf database. The OSPF link-state database (LSDB) contains all received LSAs, including Type 1 (Router) and Type 3 (Summary) LSAs that advertise routes. Even if a route is not installed in the routing table (e.g., due to a higher administrative distance or a missing route preference), the 'show ospf database' command confirms whether OSPF has received the LSA carrying that route. This directly answers the question of whether OSPF received the route, independent of route installation.

Answer

show route protocol ospf

Answer

show ospf neighbor

Answer

show interface terse

Question 15

Refer to the exhibit. What does this command accomplish?

Accepted Answer

Displays syslog messages containing the word 'error'.. The command shown filters the output of the system log file to display only lines containing the substring 'error'. This allows the administrator to quickly see log entries related to errors, rather than viewing all messages or a dedicated error log file.

Answer

Displays help for syslog messages that include 'error'.

Answer

Displays all syslog messages.

Answer

Displays the error log file.