JN0-106 Practice Test 19 — 15 Questions

Question 1

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 2

A user wants to ensure that a configuration change is applied across both Routing Engines in a dual-RE system. Which command must be used?

Accepted Answer

commit synchronize. The 'commit synchronize' command applies the candidate configuration to both Routing Engines simultaneously in a dual-RE system. This ensures configuration consistency across the master and backup RE, which is critical for high availability and seamless failover in Junos.

Answer

commit and-quit

Answer

commit confirmed

Answer

commit full

Question 3

A technician wants to view the system log messages in real time. Which command should they use?

Accepted Answer

monitor start messages. The 'monitor start messages' command is used in Junos OS to display system log messages in real time as they are generated. This is the correct command for live monitoring of system events, similar to 'tail -f' on Unix systems.

Answer

show system log

Answer

start shell

Answer

show log messages

Question 4

Tom is a junior network engineer who recently joined a service provider. He is tasked with configuring a new BGP session on an MX240 router to peer with a customer. He accesses the router via SSH and enters configuration mode using the `configure` command. He then navigates to `edit protocols bgp` and begins configuring. He sets the local AS number, adds a group named 'CUSTOMER-A', and specifies the peer IP address 192.0.2.2. After completing the configuration, he attempts to commit by typing `commit`. The system returns a syntax error and indicates that the configuration is invalid. Tom is unsure what went wrong and wants to identify the error before making any changes. What should Tom do next?

Accepted Answer

Issue the `commit check` command to validate the candidate configuration syntax.. The correct action is to issue the `commit check` command (option A), which validates the candidate configuration for syntax and semantic errors without actually committing it, exactly what Tom needs to identify the invalid statement before making changes. On Junos, `commit` itself failed with a syntax error, so running `commit check` will report the specific error location and reason while leaving the active configuration untouched. Option B (`show | compare`) only shows the diff between the candidate and the last committed configuration and does not validate syntax or explain the error. Option C (`run show configuration protocols bgp`) displays the active committed BGP configuration, not the candidate, so it would not reveal Tom's invalid edits. Option D merely re-enters the BGP hierarchy and shows the candidate text but performs no validation, so it would not identify the syntax error.

Answer

Issue the `show | compare` command to see the differences from the previous committed configuration.

Answer

Issue the `run show configuration protocols bgp` command to display the current active configuration.

Answer

Issue the `edit protocols bgp` command again to re-enter the hierarchy and review the settings.

Question 5

Your company recently acquired a small office that uses a Juniper MX router to connect to two ISPs for redundancy. The router has two uplinks: xe-0/0/0 to ISP-A (next-hop 10.0.0.1) and xe-0/0/1 to ISP-B (next-hop 10.0.1.1). The router receives a full BGP table from both ISPs. You want to prefer ISP-A for most traffic, but use ISP-B as a backup. You have configured BGP with local-preference 200 on routes from ISP-A and local-preference 100 on routes from ISP-B. After committing, you check the routing table and see that for some destinations, the route from ISP-B is active despite having lower local-preference. What is the most likely reason?

Accepted Answer

The router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised.. The correct answer is B: the router is likely not receiving the ISP-A routes for those specific prefixes, perhaps because ISP-A's BGP session is missing or the prefix is not advertised. Local-preference is evaluated before MED and IGP metric in the BGP best-path selection process, so if a route from ISP-A with local-preference 200 existed for those destinations, it would be preferred over the ISP-B route with local-preference 100. If ISP-A simply isn't advertising those prefixes (or the session is down), no ISP-A route exists to compare, so the ISP-B route becomes active. Option A is false because local-preference is a well-known discretionary attribute that is commonly set on eBGP-learned routes via inbound policy. Option C is wrong because IGP metric is only considered after local-preference and MED, so it cannot override a higher local-preference. Option D is wrong because MED is compared after local-preference, so a higher MED from ISP-A would not cause the lower-local-preference ISP-B route to win.

Answer

The local-preference is not applied to routes that are learned via eBGP; it only works for iBGP.

Answer

The IGP metric to the next-hop from ISP-B is lower, causing the route to be preferred.

Answer

The MED value from ISP-A is higher than from ISP-B, overriding the local-preference.

Question 6

You are configuring a Juniper MX router to act as a BGP route reflector for your ISP network. The router has several iBGP peers, including clients and non-clients. You have configured the route-reflector-cluster-id and set the clients. After the configuration, you notice that some prefixes are not being reflected to a specific client router. The client has a valid BGP session to the route reflector and can see other prefixes. You check the BGP routing table on the route reflector and see that the missing prefixes are present but have the 'non-routable' flag. The route reflector's BGP table shows the prefix with a next-hop that is not reachable via an IGP route. What is the most likely cause?

Accepted Answer

The next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix.. The correct answer is A: the next-hop for the missing prefixes is not reachable via the IGP on the route reflector, and the route reflector needs a route to the next-hop to advertise the prefix. In Junos, a BGP route is marked non-routable (hidden) when the next-hop cannot be resolved in the inet.0 routing table, and such unresolved routes are not eligible for advertisement to BGP peers, including route-reflector clients. Since the session is up and other prefixes are received, the issue is next-hop resolution rather than session or reflection configuration. Option B is wrong because an incorrect cluster ID would cause loop-prevention behavior (such as rejecting routes with its own cluster ID), not a non-routable flag from an unresolved next-hop. Option C is wrong because ORIGINATOR_ID suppression would drop routes originated by the same router, not mark them non-routable. Option D is wrong because next-hop-self changes the advertised next-hop to the route reflector's own address, which is locally reachable and would not cause this non-routable condition.

Answer

The route-reflector-cluster-id is set incorrectly, causing the route reflector to drop the route to prevent loops.

Answer

The ORIGINATOR_ID attribute from a previous route reflector is causing the route to be suppressed.

Answer

The route reflector is using the next-hop-self option and cannot resolve its own IP as a next-hop.

Question 7

Refer to the exhibit. Which route is active for the 192.168.1.0/24 prefix?

Accepted Answer

The OSPF route because it is marked with an asterisk.. The OSPF route is active because it is marked with an asterisk, which in this routing table indicates the route currently installed in the forwarding table for 192.168.1.0/24. When multiple routing sources offer the same prefix, the device selects one best route based on administrative distance or preference, and only that selected route is flagged as active. The static route, despite being present in the table, is not the active entry for this prefix in the exhibit. Options A, B, and C are incorrect because only one route is active, the static route is not the selected one, and at least one route is active.

Answer

Both routes are active.

Answer

The static route because it has a lower preference.

Answer

Neither route is active.

Question 8

An administrator wants to save the current configuration as a rescue configuration. Which command sequence is correct?

Accepted Answer

request system configuration rescue save. The correct command sequence to save the current configuration as a rescue configuration in Junos is 'request system configuration rescue save'. This command stores a copy of the active configuration as a rescue configuration, which can be loaded later using 'request system configuration rescue recover' if the device becomes unreachable or the configuration is corrupted. The rescue configuration is stored in a special file (rescue.conf.gz) and is not overwritten by normal commits.

Answer

copy configuration rescue

Answer

save rescue-config

Answer

commit rescue

Question 9

Refer to the exhibit. Which log file will contain messages about authorization events?

Accepted Answer

messages. In Junos, the 'messages' log file (typically /var/log/messages) records system log messages, including authorization events such as user login failures, privilege escalation attempts, and configuration changes. Authorization events are generated by the system's authentication, authorization, and accounting (AAA) framework and are logged at the 'info' severity level by default, which is captured in the messages file. The 'interactive-commands' log file specifically records CLI commands entered by users, not authorization events.

Answer

Both messages and interactive-commands

Answer

Neither

Answer

interactive-commands

Question 10

You are troubleshooting a network connectivity issue at a medium-sized company that uses Juniper EX4300 switches. Users in VLAN 100 (10.10.100.0/24) report that they cannot access a server in VLAN 200 (10.10.200.0/24). The switch has IRB interfaces configured for both VLANs and is acting as the default gateway. The IRB interfaces are up and have correct IP addresses. The server and users have correct IP configurations. 'show arp' on the switch shows incomplete entries for some hosts in VLAN 100. 'show ethernet-switching table' shows MAC addresses for users are present on the correct access ports. However, pings from the switch to a user in VLAN 100 fail. What is the most likely issue?

Accepted Answer

The switch cannot resolve ARP requests because the user's host is not responding.. The 'incomplete' entries in the 'show arp' output indicate that the switch sent ARP requests for hosts in VLAN 100 but received no replies. Since the switch is the default gateway, it must resolve the Layer 2 MAC address of each host to forward traffic. If a user's host is not responding to ARP (e.g., due to a firewall, misconfiguration, or the host being offline), the switch cannot complete the ARP cache entry, causing pings from the switch to fail and potentially disrupting inter-VLAN routing.

Answer

Spanning Tree Protocol is blocking the user ports.

Answer

A static MAC address entry for the server is missing.

Answer

The IRB interface for VLAN 100 is not configured with a proxy ARP.

Question 11

Refer to the exhibit. An administrator wants to ensure that log messages are stored even if the remote syslog server becomes unavailable. What additional configuration is required?

Accepted Answer

set system syslog file messages any any. Configuring a local log file with `set system syslog file messages any any` ensures that log messages are stored locally on the device, even if the remote syslog server becomes unavailable. This provides a persistent local copy of logs that can be reviewed later, independent of the remote server's reachability.

Answer

set system syslog archive world-readable

Answer

set system syslog host 10.10.10.1 facility-override

Answer

set system syslog rate-limit 1000

Question 12

What is the purpose of the 'commit confirmed' command in Junos OS?

Accepted Answer

It allows the administrator to test a configuration change with automatic rollback if confirmation is not received. The 'commit confirmed' command in Junos OS applies a candidate configuration change and starts a confirmation timer (default 10 minutes). If the administrator does not issue a 'commit' command before the timer expires, the system automatically rolls back to the previous active configuration. This allows safe testing of changes, especially over remote connections, preventing lockout if the change breaks connectivity.

Answer

It compares the candidate configuration with the active configuration

Answer

It permanently saves the candidate configuration to the startup configuration

Answer

It confirms that a previous commit was successful

Question 13

Refer to the exhibit. What is the most likely cause of this BGP route being hidden?

Accepted Answer

The next-hop 192.168.100.1 is not reachable via any active route.. In JUNOS, a BGP route is hidden when the next-hop address is not reachable via any active route in the routing table. The show route protocol bgp command displays the route as hidden if the next-hop 192.168.100.1 is not resolvable, because BGP requires a valid IGP or static route to the next-hop for the route to be considered active and installed in the forwarding table.

Answer

The route has a higher preference than another route.

Answer

The BGP session to 10.0.0.2 is down.

Answer

The prefix 10.1.1.0/24 is filtered by an import policy.

Question 14

Which THREE modes can be used to enter configuration mode in Junos? (Choose three.)

Accepted Answer

configure private. In Junos, the CLI configuration mode can be entered with different locking behaviors: 'configure private' (option B) gives each user a private candidate configuration so concurrent users don't interfere, 'configure shared' (option C) lets multiple users edit the same shared candidate configuration, and 'configure exclusive' (option E) locks the candidate configuration so only one user can make changes at a time. These three are valid Junos commands for entering configuration mode with the specified locking semantics. Options A ('configure static') and D ('configure dynamic') are not valid Junos configuration-mode commands; there is no 'static' or 'dynamic' configure variant in Junos.

Answer

configure static

Answer

configure dynamic

Question 15

An administrator wants to navigate to the configuration mode to make changes to the device. Which command should be used?

Accepted Answer

configure. The correct command to enter configuration mode on a Juniper device is 'configure'. This command transitions the CLI from operational mode to configuration mode, allowing the administrator to make changes to the device's configuration. In JUNOS, the CLI has two distinct modes: operational mode (for monitoring and troubleshooting) and configuration mode (for modifying the active or candidate configuration).

Answer

set

Answer

edit

Answer

cli