JN0-106 Junos OS Fundamentals Practice Test 4 — 15 Questions

Question 1

Which THREE commands are valid in Junos operational mode? (Choose three.)

Accepted Answer

show interfaces terse. 'show interfaces terse' is a valid operational mode command that displays a concise summary of interface status and configuration. Operational mode in Junos is used for monitoring, troubleshooting, and viewing the current state of the device, and 'show' commands are the primary tools for this purpose.

Answer

set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.1/24

Answer

commit and-quit

Question 2

A network engineer is troubleshooting connectivity between two VLANs on the same Juniper EX switch. Hosts in VLAN 100 cannot ping hosts in VLAN 200. The switch has an IRB interface configured for each VLAN. Which configuration is most likely missing?

Accepted Answer

The IRB interfaces are not assigned to the same routing instance. For hosts in different VLANs to communicate through an EX switch, the IRB interfaces must belong to the same routing instance to enable inter-VLAN routing. By default, each IRB is placed in the default routing instance (inet.0), but if they are assigned to separate routing instances, no route exists between them, breaking Layer 3 forwarding. Option C directly addresses this missing configuration.

Answer

Spanning Tree Protocol is not enabled on the switch

Answer

The switchport mode is set to access instead of trunk

Answer

DHCP relay is not configured on the IRB interfaces

Question 3

Which TWO statements about the Junos OS configuration hierarchy are correct? (Choose two.)

Accepted Answer

Configuration is organized in a hierarchical structure with levels. The Junos OS configuration is organized in a hierarchical structure, resembling a tree with defined levels (e.g., [edit interfaces], [edit protocols ospf]). This hierarchy allows for logical grouping of configuration statements, making it easier to manage and navigate. The structure is enforced by the Junos CLI and the configuration database, which uses a set-based model rather than a flat file.

Answer

All configuration is stored in a flat file with line numbers

Answer

The hierarchy is stored in multiple configuration files that are merged at boot

Answer

Configuration values are inherited from the root level automatically

Question 4

Which TWO commands can be used to save the current Junos configuration to a file on the local flash drive? (Choose two.)

Accepted Answer

show configuration | save /config/backup.conf. The 'show configuration | save' command pipes the current active configuration (from the candidate or active configuration) directly to a file, allowing you to save it to a specified path like /config/backup.conf on the local flash drive. This is a standard method for exporting the running configuration to a file in Junos.

Answer

file copy /config/juniper.conf.gz /config/backup.conf

Answer

request system configuration rescue save

Answer

copy flash:juniper.conf.gz /config/backup.conf

Question 5

Which THREE statements about the Junos OS file system are true? (Choose three.)

Accepted Answer

The active configuration is stored in the /config directory. The active configuration in Junos OS is stored as a file named `junos.conf` in the `/config` directory. This file is used by the system to load the running configuration at boot time, and it is distinct from the candidate configuration stored in `/var/db/config`.

Answer

The /etc directory contains all log files

Answer

The /altroot directory is used for user-uploaded files

Question 6

Your enterprise network uses Juniper EX4300 switches in a collapsed core design with RSTP (802.1w) as the Layer 2 loop prevention protocol. You add a new EX2300 switch to an access closet and connect it to two different core switches using two uplink interfaces configured in an LACP LAG. After connecting the new switch, you notice intermittent connectivity issues across the entire network, with some devices reporting temporary packet loss. The issue occurs sporadically, especially during configuration changes or when links flap. You suspect the problem is related to RSTP. Upon investigation, you see that the new switch's uplink interfaces are both in the forwarding state, but occasionally one of them transitions to blocking and then back to forwarding. What is the most likely cause of the intermittent issues?

Accepted Answer

The LAG is not recognized as a single logical link by RSTP, causing RSTP to see two separate links and create a loop. B is correct because the two uplinks are connected to two different core switches. A standard LACP LAG requires both links to terminate on the same remote switch. Since they terminate on different switches, the LAG does not form and RSTP sees two separate physical links. This creates a loop between the EX2300 and the core (via the core switches' interconnection), so RSTP blocks one link. When configuration changes or link flaps occur, RSTP recalculates and the blocked port can temporarily transition to forwarding, causing intermittent packet loss.

Answer

The LACP system priority is set too low on the new switch, causing it to lose LACP negotiations

Answer

The uplink interfaces are configured as alternate ports instead of root ports

Answer

The new switch has a different root bridge priority, causing it to become the root and disrupting topology

Question 7

Which two statements correctly describe Junos OS login classes? (Choose two.)

Accepted Answer

They are defined under the [edit system login class] hierarchy.. Junos OS login classes are defined under the [edit system login class] hierarchy in the configuration. This hierarchy allows administrators to create custom classes that specify the permissions and access levels for users, such as read-only or superuser access.

Answer

They allow users to enter only operational mode.

Answer

They are automatically assigned to all users by default.

Answer

They cannot be modified after creation.

Question 8

Which TWO statements are correct regarding the Junos OS configuration hierarchy?

Accepted Answer

The 'show | compare' command displays differences between the candidate and active configurations.. The correct answers are C and E. Option C is correct because the 'show | compare' command displays the differences between the candidate configuration and the active configuration. Option E is correct because the 'set' command is used to modify the candidate configuration by adding or changing configuration statements. Option A is incorrect because the 'commit check' command only validates the candidate configuration for syntax errors; it does not apply the configuration to the active configuration—that is done by the 'commit' command. Option B is incorrect because the 'load replace' command replaces the entire candidate configuration with the configuration from a file; it does not merge—merging is done by the 'load merge' command. Option D is incorrect because 'rollback 0' reverts the active configuration to the most recently committed configuration, not the candidate configuration; rolling back the candidate configuration is done with 'rollback' followed by a non-zero number.

Answer

The 'commit check' command applies the candidate configuration to the active configuration.

Answer

The 'load replace' command merges a configuration file into the candidate configuration.

Answer

The 'rollback 0' command reverts the candidate configuration to the previous state.

Question 9

Based on the exhibit, the interface appears to be up and has an IP address, but the 'monitor traffic' output shows no packets. What is the most likely cause?

Accepted Answer

The interface is not in promiscuous mode, and 'monitor traffic' requires that mode to capture packets.. 'monitor traffic' captures packets by default only on the management interface or on interfaces configured in promiscuous mode. The exhibit shows an interface that is up with an IP address, but if it is not in promiscuous mode, 'monitor traffic' will not capture packets on that interface. Option B is incorrect because the interface is up, not administratively down. Option C is incorrect because an unnumbered interface still has an IP address derived from another interface, and the exhibit shows an IP address. Option D is incorrect because there is no indication of a firewall filter blocking traffic; the issue is with packet capture, not traffic flow.

Answer

The interface is administratively down.

Answer

The interface is an unnumbered Ethernet interface.

Answer

A firewall filter is blocking all inbound traffic.

Question 10

A network engineer is configuring a new Juniper MX router to replace an existing core router. The engineer has applied several configuration changes and wants to ensure that the new configuration can be tested safely. If the test fails (e.g., loss of management connectivity), the router should automatically revert to the previous configuration after a 5-minute period. The engineer performs a commit confirmed with a timeout of 5 minutes. After 4 minutes, the engineer verifies that the change is successful and wants to make it permanent. Which action should the engineer take to ensure the configuration persists?

Accepted Answer

Issue a standard 'commit' command to confirm the configuration.. After a 'commit confirmed' with a timeout, issuing a standard 'commit' command makes the configuration permanent and stops the automatic rollback. Option A is wrong because 'rollback 0' reverts to the previously committed configuration, undoing the changes. Option B is wrong because reissuing 'commit confirmed 5' restarts the timer but does not finalize the configuration; the configuration would still be reverted if not confirmed before the new timeout. Option C is wrong because reloading the router would cause an interruption and does not confirm the configuration; on reboot, the router would apply the previous configuration (since the confirmed commit was not finalized).

Answer

Issue the 'rollback 0' command, then commit.

Answer

Issue the 'commit confirmed 5' command again to reset the timer.

Answer

Issue the 'request system reboot' command to reload the router.

Question 11

A junior engineer is troubleshooting connectivity issues and wants to trace the path packets take to a remote destination. Which Junos command should be used?

Accepted Answer

traceroute. The 'traceroute' command in Junos is specifically designed to trace the path packets take to a remote destination by sending UDP probes with increasing TTL values and analyzing ICMP Time Exceeded messages from intermediate routers. This directly addresses the junior engineer's need to map the Layer 3 path and identify where connectivity failures occur.

Answer

monitor traffic

Answer

show route

Answer

ping

Question 12

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 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

You are a network administrator for a large enterprise. You have a Juniper SRX firewall that is used as the primary internet gateway. Users are reporting that they are unable to access certain external websites. You check the device and find that the security policies appear correct, and the routing is in place. You suspect that the issue might be related to the DNS resolution. You want to verify that the device can resolve DNS names and that the DNS server configuration is correct. Which command should you use to test DNS resolution from the Juniper device?

Accepted Answer

ping <external website FQDN>. The `ping` command with a fully qualified domain name (FQDN) forces the Juniper device to perform a DNS resolution before sending ICMP echo requests. If the device cannot resolve the FQDN, the ping will fail with a 'hostname not found' error, directly indicating a DNS configuration or reachability issue. This tests both the DNS server configuration and the device's ability to resolve names, which is essential for verifying DNS functionality.

Answer

show system connections

Answer

traceroute <external website FQDN>

Answer

show dns name-server

Question 15

Which THREE of the following statements are true regarding Junos OS commit operations?

Accepted Answer

The 'commit check' command validates the candidate configuration without activating it.. The 'commit check' command validates the candidate configuration for syntax and semantic errors without activating it. This allows an administrator to verify changes before making them active, preventing potential misconfigurations from disrupting network operations.

Answer

You can run multiple commit scripts during a single commit operation.

Answer

The rollback command reverts to the current active configuration.