JN0-106 Practice Questions 2 — 50 Questions

Question 1

A switch receives a unicast frame with a destination MAC address that is present in its MAC address table. How does the switch process the frame?

Accepted Answer

It forwards the frame only out of the port associated with that MAC address. When a switch receives a unicast frame and the destination MAC address is already in its MAC address table, it performs a lookup and forwards the frame only out of the specific port associated with that MAC address. This is the fundamental switching behavior known as 'unicast forwarding' or 'filtering,' which avoids unnecessary flooding and preserves bandwidth.

Answer

It sends the frame back to the source port

Answer

It floods the frame to all ports except the receiving port

Answer

It drops the frame

Question 2

Scenario: Your company has a Juniper MX Series router at a branch office running Junos 18.4. The device has been in production for two years with a stable configuration. Yesterday, a senior engineer made several changes to the OSPF configuration to optimize routing for a new link. They committed the changes and left for the day. This morning, the branch office experiences intermittent connectivity, and the OSPF neighbor relationships are flapping. You suspect the recent OSPF changes caused the issue. You have remote console access to the router. The goal is to restore network stability as quickly as possible while preserving the ability to re-apply the changes after troubleshooting. Which course of action should you take?

Accepted Answer

Use 'rollback 1' to revert to the configuration before the changes, then 'commit confirmed 10' to verify stability.. 'rollback 1' reverts the active configuration to the previous committed version (before the problematic OSPF changes), and 'commit confirmed 10' applies that rollback with a 10-minute confirmation timer. If connectivity stabilizes, the rollback becomes permanent; if not, the router automatically reverts to the previous configuration, ensuring no prolonged outage. This approach restores stability quickly while preserving the ability to later re-apply and test the OSPF changes in a controlled manner.

Answer

Use 'deactivate protocols ospf' to disable OSPF entirely and then manually re-enable pieces.

Answer

Immediately delete the OSPF configuration sections that were changed and re-add the original settings manually.

Answer

Perform a 'load factory-default' and 'commit' to reset the device to base settings, then reconfigure from backup.

Question 3

Which TWO commands can be used to view the current routing table entries for IPv4 unicast routes?

Accepted Answer

show route table inet.0. `show route table inet.0` explicitly displays the IPv4 unicast routing table (inet.0) in Junos. Option D is correct because `show route` without any filter defaults to showing all routes in the inet.0 table, which is the primary IPv4 unicast routing table.

Answer

show route protocol static

Answer

show forwarding-table

Answer

show route table inet6.0

Question 4

You are a junior network engineer at a company that uses Juniper MX routers. You are troubleshooting a connectivity issue on a branch router. The branch router has two upstream links to the corporate network: ge-0/0/0 (10.1.1.1/30, connected to core router A) and ge-0/0/1 (10.1.1.5/30, connected to core router B). The branch router runs OSPF and has a default route learned from both upstream routers. The routing table shows two equal-cost default routes via both next hops. However, traffic from the branch to the corporate network is experiencing intermittent high latency and some packet loss. You suspect that asymmetric routing is causing issues because the return traffic is not following the same path. You want to influence the router to prefer one upstream link for all traffic to the corporate network. You have decided to adjust the OSPF metric on the branch router to make the link to core router A more preferred. You are in configuration mode on the branch router. Which single configuration change will accomplish this goal?

Accepted Answer

set protocols ospf area 0 interface ge-0/0/1 metric 200. Setting the OSPF metric on interface ge-0/0/1 to a higher value (200) increases the cost of that link, making the default route via ge-0/0/0 (which retains the default OSPF metric of 1 on a Gigabit Ethernet interface) more preferred. This influences the branch router to use the lower-cost path through core router A for all traffic to the corporate network, resolving asymmetric routing issues.

Answer

set interfaces ge-0/0/1 unit 0 family inet cost 200

Answer

set protocols ospf area 0 interface ge-0/0/1 passive

Answer

set interfaces lo0 unit 0 family inet address 10.0.0.1/32 metric 100

Question 5

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 6

A Juniper device receives several routes to the same destination prefix from different routing protocols. Which parameter is used first to select the active route?

Accepted Answer

Route preference (administrative distance). When a Juniper device receives multiple routes to the same destination prefix from different routing protocols, the route preference (also known as administrative distance) is the first tiebreaker used to select the active route. Each protocol has a default preference value (e.g., OSPF internal routes have a preference of 10, while static routes have a preference of 5), and the route with the lowest preference is chosen as active. This occurs before any metric or other path attribute is considered.

Answer

Metric

Answer

AS path length

Answer

Local preference

Question 7

A company has two Juniper routers in a high-availability cluster with dual Routing Engines. The administrator performs a commit on the primary RE. What is the effect of using the 'commit synchronize' command?

Accepted Answer

It commits the configuration on both Routing Engines simultaneously.. The 'commit synchronize' command on Juniper routers with dual Routing Engines ensures that the configuration is committed on both the primary and backup REs simultaneously. This is critical for maintaining configuration consistency in a high-availability cluster, as it prevents a split-brain scenario where the backup RE has a different active configuration than the primary. The command performs a full commit (including validation and activation) on both REs, not just a check.

Answer

It performs a commit check on both REs but does not activate the config.

Answer

It commits the configuration only on the primary RE.

Answer

It commits the configuration only on the backup RE.

Question 8

A company runs a Juniper SRX firewall cluster consisting of two nodes (node0 primary, node1 secondary). The cluster has been stable. During maintenance, you modify the configuration on node0 and commit. After the commit, the cluster status shows node1 as 'ineligible'. You suspect a configuration mismatch. What should you do to synchronize the configuration without disrupting traffic?

Accepted Answer

On the primary node, execute 'commit synchronize'.. The 'commit synchronize' command on the primary node (node0) pushes the active configuration to the secondary node (node1) and commits it on both nodes, ensuring configuration consistency without requiring a reboot or traffic disruption. In a Juniper SRX cluster, the primary node is the authoritative source for configuration synchronization, and this command is the standard method to resolve a configuration mismatch that causes a node to become 'ineligible'.

Answer

Reboot both nodes to force synchronization.

Answer

Manually copy the configuration file from primary to secondary.

Answer

On the secondary node, execute 'commit synchronize'.

Question 9

A network engineer suspects a hardware issue on an interface. Which command provides the most detailed hardware error counters, including CRC errors, framing errors, and runts?

Accepted Answer

show interfaces extensive. The 'show interfaces extensive' command provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command displays per-interface statistics at the physical layer, such as input errors, output errors, and specific error types like frame, runts, giants, and CRC errors, which are essential for diagnosing hardware issues.

Answer

show interfaces diagnostics optics

Answer

show interfaces detail

Answer

show log messages

Question 10

A router receives a packet with destination IP 10.1.1.100. The routing table contains two entries: a static route to 10.1.1.0/24 via 192.168.1.1, and an OSPF route to 10.1.1.0/25 via 192.168.2.1. Which route will the router use?

Accepted Answer

The OSPF route to 10.1.1.0/25. The router will use the OSPF route to 10.1.1.0/25 because it has a longer prefix length (/25) than the static route (/24). Juniper Junos uses the most specific (longest) prefix match in the routing table, regardless of administrative distance or protocol preference. The destination IP 10.1.1.100 falls within the 10.1.1.0/25 range (10.1.1.0–10.1.1.127), so the /25 route is more specific and thus preferred.

Answer

The router drops the packet due to a routing conflict

Answer

The static route to 10.1.1.0/24

Answer

Both routes are used for load balancing

Question 11

Refer to the exhibit. A host connected to ge-0/0/1 cannot reach a host connected to ge-0/0/2 even though both are in VLAN10. What is the most likely cause?

Accepted Answer

The hosts are configured with IP addresses on different subnets.. Although both hosts are in the same VLAN and can communicate at Layer 2 (MAC addresses), IP communication requires them to be on the same IP subnet. If the hosts have IP addresses on different subnets, they will attempt to use a default gateway for routing. Without a router or IRB interface configured, the traffic cannot be delivered, leading to unreachability.

Answer

VLAN10 is not defined in the global VLAN configuration.

Answer

An IRB interface for VLAN10 is not configured.

Answer

The interface ge-0/0/2 is configured as a trunk port.

Question 12

A network engineer configures a static route to 10.0.0.0/8 with a preference of 20. An OSPF internal route to 10.0.0.0/8 has a default preference of 10. Which route will be active in the routing table?

Accepted Answer

The OSPF route, because of lower preference.. In Junos, the active route in the routing table is determined by the lowest preference value. OSPF internal routes have a default preference of 10, while static routes have a default preference of 5, but here the static route is configured with a preference of 20. Since OSPF's preference (10) is lower than the static route's preference (20), the OSPF route is chosen as active.

Answer

Both routes, because they have different protocols.

Answer

Neither, because of a conflict.

Answer

The static route, because it is manually configured.

Question 13

An engineer needs to apply a configuration change that adds a new static route to the Junos device. The engineer wants to ensure the change takes effect immediately and is persistent across reboots. Which command should the engineer use?

Accepted Answer

commit. The 'commit' command is correct because it immediately activates the candidate configuration (including the new static route) and makes it the active configuration that survives a reboot. Junos uses a two-stage configuration model where changes are first made to the candidate configuration and then committed to become the active, persistent configuration.

Answer

load override

Answer

commit confirmed

Answer

rollback

Question 14

A network administrator needs to temporarily disable a set of configuration statements for testing without deleting them. Which approach should be used?

Accepted Answer

use the 'deactivate' command to mark the statements inactive. The 'deactivate' command in Junos allows an administrator to temporarily disable a set of configuration statements without removing them from the configuration. When a statement is deactivated, it is prefixed with 'inactive:' in the configuration hierarchy, and the commit operation ignores it. This is ideal for testing changes, as the statements can be easily re-enabled using the 'activate' command.

Answer

delete the statements and later re-add from a backup

Answer

comment out the lines using #

Answer

set the configuration to a different group and remove apply-groups

Question 15

A network engineer is designing a redundant network with two Juniper routers running VRRP. The virtual IP address is 10.0.0.1. Both routers are configured as VRRP group 1. What is the purpose of the 'priority' parameter in VRRP configuration?

Accepted Answer

It determines the master router election.. In VRRP, the 'priority' parameter (range 1-254, default 100) is used to elect the master router. The router with the highest priority becomes the master for the virtual IP address 10.0.0.1, ensuring redundancy by taking over traffic forwarding if the current master fails.

Answer

It sets the interval for VRRP advertisements.

Answer

It determines the virtual MAC address.

Answer

It changes the virtual IP address.

Question 16

An engineer notices that a Juniper device is not saving configuration changes across reboots. What is the most likely cause?

Accepted Answer

The candidate configuration was not committed.. In Junos OS, configuration changes are stored in a candidate configuration and only become active and persistent across reboots after a 'commit' operation. Without a commit, the changes remain in the candidate buffer and are discarded upon reboot, causing the device to revert to the last committed configuration.

Answer

The rescue configuration is not set.

Answer

The device is booting from factory-default configuration.

Answer

The command 'request system reboot' was used instead of 'commit'.

Question 17

An engineer wants to apply a candidate configuration and automatically revert to the previous configuration after 10 minutes if the commit is not confirmed. Which command should be used?

Accepted Answer

commit confirmed 10. The `commit confirmed 10` command commits the candidate configuration and starts a 10-minute timer. If the commit is not explicitly confirmed with another `commit` command within that time, Junos automatically reverts to the previous configuration. This is the correct method for a timed automatic rollback after a commit.

Answer

commit at 10

Answer

set system commit timer 10

Answer

commit check

Question 18

A network engineer configures a static route to a remote network. They want the route to be automatically removed from the routing table if the directly connected interface used to reach the next hop fails. Which configuration approach should be used?

Accepted Answer

Configure the next-hop as the interface name.. Configuring the next-hop as an interface name (e.g., ge-0/0/0) creates a static route that is automatically removed from the routing table when that interface goes down. This is due to the route being 'qualified' by the interface's operational state; if the interface fails, the route is withdrawn. In contrast, using an IP address as the next-hop does not tie the route to the interface's state, so the route remains even if the interface fails, as long as the next-hop is reachable via another path.

Answer

Configure a higher metric on the static route.

Answer

Configure a preference of 0 on the static route.

Answer

Configure the next-hop as an IP address.

Question 19

Which command is used to verify that the current active configuration is the same as the candidate configuration?

Accepted Answer

show | compare. The command `show | compare` displays the differences between the candidate configuration and the active (committed) configuration. If there are no differences, the candidate configuration is identical to the active configuration. This is the correct way to verify whether the candidate configuration matches the active configuration in Junos.

Answer

commit check

Answer

show configuration

Answer

show system configuration

Question 20

A router has two routes to the same destination: one with preference 10 and metric 5, and another with preference 15 and metric 3. Which route will be installed in the forwarding table?

Accepted Answer

The route with preference 10.. In Junos, the route preference (administrative distance) is the primary criterion for selecting the best route to a destination. The route with preference 10 is preferred over the route with preference 15, regardless of metric values. The route with preference 10 is installed in the forwarding table.

Answer

The route with metric 3.

Answer

Neither route is installed.

Answer

Both routes are installed if ECMP is enabled.