JNCIA-JUNOS Practice Test 15 — 15 Questions

Question 1

Refer to the exhibit. Based on the output, which statement is true?

Accepted Answer

The router hostname is router1.. The output shows the system prompt ending with 'router1>', which indicates the hostname is set to 'router1'. In Junos, the CLI prompt format is 'hostname>', so this directly confirms the router hostname. Option D is correct because the prompt explicitly displays 'router1' as the active hostname.

Answer

The admin user has read-only access.

Answer

The interface ge-0/0/0 has been disabled.

Answer

The root password is stored in plaintext.

Question 2

Which THREE CLI features are available in Junos OS to assist with command entry?

Accepted Answer

? (question mark) for context-sensitive help.. Option A is correct because the question mark (?) provides context-sensitive help in Junos OS, displaying available commands, options, and syntax at any point in the CLI. This is a fundamental feature for command discovery and verification, especially when the exact command syntax is not known.

Answer

Ctrl+R to repeat the last command.

Answer

Ctrl+Z to undo the last command.

Question 3

Which TWO commands can be used to view the current running configuration?

Accepted Answer

show configuration | display set. Option B is correct because the 'show configuration | display set' command outputs the current active configuration in 'set' format, which is a flat, line-by-line representation of configuration statements. Option D is correct because 'show configuration' without any pipe modifier displays the entire running configuration in its native hierarchical format. Both commands allow you to view the current running configuration, just in different presentation styles.

Answer

show configuration | display inheritance

Answer

show configuration | match

Answer

show configuration | compare

Question 4

Which two commands can be used to view the candidate configuration in set format? (Choose two.)

Accepted Answer

show | display set (in configuration mode). Option C is correct because in configuration mode, the 'show | display set' command outputs the candidate configuration as a series of 'set' commands, which is a compact and script-friendly format. Option D is also correct because the same output can be achieved in operational mode using 'show configuration | display set', which displays the candidate configuration from the operational CLI context.

Answer

show configuration | display set | no-parenthesis

Answer

show | set

Answer

show configuration | display inherited

Question 5

Refer to the exhibit. What is the purpose of the 'unit 0' statement?

Accepted Answer

Defines a logical interface.. In Junos, the 'unit 0' statement is used to define a logical interface (also known as a subinterface) under a physical interface. Every physical interface must have at least one logical unit, and unit 0 is the default logical interface that carries Layer 3 configuration such as IP addresses. This is fundamental to Junos architecture, where all protocol configurations are applied at the logical unit level, not the physical interface level.

Answer

Enables IPv6.

Answer

Sets the MTU.

Answer

Defines a physical interface.

Question 6

A network administrator accidentally deleted a vital part of the configuration while in configuration mode. They need to revert to the previous configuration without losing recent changes that are correct. Which action should they take?

Accepted Answer

rollback 1. Option B is correct because the 'rollback 1' command reverts the candidate configuration to the most recently committed configuration (the previous active configuration), while preserving any uncommitted changes that were made after the rollback. This allows the administrator to discard the accidental deletion and then manually re-apply only the correct recent changes before committing.

Answer

deactivate

Answer

delete

Answer

rollback 0

Question 7

An engineer wants to view system log messages as they are generated in real-time. Which command should they use?

Accepted Answer

monitor log messages. The 'monitor log messages' command in Junos OS provides a real-time view of system log messages as they are generated, similar to the 'tail -f' command on Unix systems. It streams new log entries to the terminal without requiring manual refresh, making it ideal for live monitoring of events.

Answer

start log messages

Answer

request system log

Answer

show log messages

Question 8

Refer to the exhibit. An engineer runs the command shown. What does this output indicate?

Accepted Answer

The candidate configuration has an IP address change.. The output shows the candidate configuration differs from the committed configuration, as indicated by the 'show | compare' command displaying a change under the [edit interfaces ge-0/0/0 unit 0 family inet] hierarchy. Specifically, it shows the address 192.168.1.1/24 being replaced with 192.168.1.2/24, which is an IP address change. This confirms option B is correct because the candidate configuration has an IP address change that has not yet been committed.

Answer

The candidate configuration matches the committed configuration.

Answer

The rollback 0 configuration is being displayed.

Answer

The interface ge-0/0/0 has been deleted.

Question 9

An engineer wants to see the differences between the active configuration and the candidate configuration. Which command should they use?

Accepted Answer

'show | compare'. Option D, 'show | compare', is correct because in the Junos CLI, the pipe (|) operator can be used to filter or modify the output of any operational mode command. When used with the 'compare' argument after 'show', it displays the differences between the active configuration and the candidate configuration. This is the standard syntax for comparing configurations in Junos.

Answer

'show configuration | display set'

Answer

'show configuration | compare'

Answer

'run show configuration | compare'

Question 10

A network engineer is troubleshooting a BGP session that is not establishing. They want to see the BGP configuration details for peer 10.0.0.1. They type 'show configuration protocols bgp group external peer 10.0.0.1' but receive 'error: syntax error'. They are in operational mode. What is the most likely issue?

Accepted Answer

The keyword 'peer' should be 'neighbor'.. In Junos OS, the correct keyword to reference a BGP peer in operational mode commands is 'neighbor', not 'peer'. The command 'show configuration protocols bgp group external neighbor 10.0.0.1' would display the configuration for that specific peer. Using 'peer' causes a syntax error because Junos does not recognize that keyword in this context.

Answer

The peer IP 10.0.0.1 is not configured on the device.

Answer

The command should be 'show configuration protocols bgp group external | match 10.0.0.1'.

Answer

They need to enter configuration mode first.

Question 11

An engineer needs to apply a configuration change to all interfaces except the management interface (fxp0). Which approach is most efficient?

Accepted Answer

Create a configuration group that includes all interfaces and use apply-groups-except to exclude fxp0.. Option C is correct because configuration groups with apply-groups-except allow you to define a common configuration template (e.g., all interfaces) and then selectively exclude specific interfaces (e.g., fxp0) from inheriting those settings. This approach is efficient, scalable, and avoids manual per-interface configuration or risky regex patterns that might inadvertently match unintended interfaces.

Answer

Manually configure each interface individually.

Answer

Use wildcard set with regex to match all interfaces except fxp0.

Answer

Use the 'set interfaces fxp0 disable' command and then apply changes to all interfaces.

Question 12

A network engineer sees an unknown unicast flood on a Juniper EX switch. Which mechanism is most effective at reducing such floods?

Accepted Answer

Enable storm control for unknown unicast traffic.. Unknown unicast flooding occurs when a switch does not have a MAC address entry for a destination, causing it to flood the frame out of all ports in the VLAN except the ingress port. Storm control for unknown unicast traffic (set using `set ethernet-switching-options storm-control interface <interface> unknown-unicast`) directly limits the rate of such flooded traffic, preventing excessive bandwidth consumption. This is the most effective mechanism because it specifically targets and rate-limits unknown unicast floods without altering MAC learning or aging behavior.

Answer

Configure static MAC addresses for all endpoints.

Answer

Increase the MAC address table aging time.

Answer

Disable MAC learning on trunk interfaces.

Question 13

An engineer enables Spanning Tree PortFast on a switch port connected to a host. Later, another switch is connected to that same port, causing a loop. What feature could have prevented this?

Accepted Answer

BPDU guard. BPDU guard is the correct answer because it disables a port configured with PortFast if a BPDU is received, preventing loops when a switch is accidentally connected. In this scenario, PortFast was enabled for a host, but connecting another switch caused BPDUs to be sent, which BPDU guard detects and shuts down the port to break the loop.

Answer

Loop guard

Answer

Root guard

Answer

UplinkFast

Question 14

A company uses a Juniper MX router to connect two branch offices via a point-to-point link. The link is flapping. Which command would you use to check the interface errors on the link?

Accepted Answer

show interfaces ge-0/0/0 extensive. The 'show interfaces ge-0/0/0 extensive' command provides detailed interface statistics, including error counters such as CRC errors, frame errors, and link state transitions. This is the most comprehensive command to diagnose why a point-to-point link is flapping, as it reveals physical-layer issues that cause the interface to go up/down repeatedly.

Answer

show log messages

Answer

show configuration interfaces ge-0/0/0

Answer

show interfaces ge-0/0/0 terse

Question 15

Which field in an Ethernet frame is used by a switch to learn which source MAC address belongs to which port?

Accepted Answer

Source MAC address. A switch learns MAC address-to-port mappings by examining the source MAC address field of incoming Ethernet frames. When a frame arrives on a port, the switch records the source MAC address and associates it with that port in its MAC address table, enabling future frames destined for that MAC to be forwarded only to the correct port.

Answer

Ethertype field

Answer

Destination MAC address

Answer

VLAN ID field

JNCIA-JUNOS Practice Test 15 — 15 Questions

Exhibit

JNCIA-JUNOS Practice Test 15 — 15 Questions

Exhibit