JN0-106 Exam Questions and Answers

Use the 'commit confirmed' command with a timeout.

The 'commit confirmed' command with a timeout (e.g., 'commit confirmed 5') activates the configuration for a temporary interval, defaulting to 10 minutes. If the administrator does not issue a confirming 'commit' before the timer expires, Junos automatically rolls back to the previous configuration. This self-reverting behavior prevents permanent lockouts caused by misconfigured access settings.

show interfaces terse ge-0/0/1

The show interfaces terse ge-0/0/1 command displays each interface as a single line containing the key operational states: administrative status (enabled/disabled), link state (up/down), and active protocol addresses. For the specified interface ge-0/0/1, this reveals immediately whether the interface is physically connected and configured for operation, without the noise of packet counters or detailed error statistics. It is the standard one-shot operational inquiry for a quick health check.

show route table inet.0

The `show route table inet.0` command is the correct choice because `inet.0` is the default IPv4 unicast routing table on Junos. When a junior engineer needs to investigate a generic routing issue involving IPv4 destinations, this command displays the active routes, protocol next-hops, and preference/metric values that determine how packets are forwarded. It directly exposes whether the expected route is present, hidden, or missing, which is the first step in diagnosing reachability problems. Unlike protocol-specific or forwarding-table views, this master table includes all protocols that contribute to IPv4 forwarding decisions.

configure

The 'configure' command is the correct Junos operational-mode command used to enter configuration mode, where the active or candidate configuration can be viewed and manipulated. When you type 'configure' at the operational prompt, the CLI switches to the configuration hierarchy, and the prompt changes to 'edit' (e.g., 'user@router#'). Variants like 'configure exclusive' or 'configure private' provide additional control over locking or private copies, but the base command is the standard entry point. Thus, 'configure' is the right answer.

monitor start messages

monitor start messages streams real-time log messages to the terminal from the messages log file, satisfying the requirement to view live logging. It differs from show log messages, which displays existing entries rather than continuously tailing new output.

rollback 1

Rollback 1 loads the configuration committed immediately before the current one into the candidate configuration. This allows a network engineer to undo the most recent commit and return to the prior operational state, though the resulting candidate must still be committed by running commit. Since the goal is to revert to the previous configuration, rollback 1 is the correct command.

show bgp neighbor x.x.x.x

show bgp neighbor x.x.x.x is the primary troubleshooting command for BGP peering. It displays the session state (Idle, Connect, Active, OpenConfirm, Established), timers, TCP connection details, and per-neighbor capabilities. Crucially, it shows the counts of received and accepted prefixes, and a separate count of rejected prefixes, along with the policy names that caused that rejection. This allows an engineer to quickly determine whether the session is up but the exchange is failing, or whether the session itself is down.

commit confirmed

The 'commit confirmed' command makes the candidate configuration active and then automatically rolls back to the previous configuration if the engineer does not issue a confirming commit within the default timeout interval (10 minutes, configurable). This is essential when configuring a new router remotely, because it ensures that a mistaken change that severs the management session will be undone automatically, letting the engineer regain access.

Apply a firewall filter on the loopback interface (lo0) to protect the device

The loopback interface (lo0) represents the device's control plane, and all traffic destined to the device's own IP addresses—such as SSH, SNMP, BGP, and OSPF—is processed through it, regardless of the physical ingress interface. Applying a firewall filter to lo0 in the input direction provides a single, centralized point to secure management and routing protocol access. This Juniper-recommended practice ensures consistent protection and simplifies administration, as the filter is applied once rather than on every interface.

set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.2/24 secondary

This is the correct Junos syntax for adding an additional IP address while keeping the existing primary address intact. The secondary keyword immediately follows the address prefix within the family inet address hierarchy, telling the configuration engine that this address is not the primary. You can configure multiple secondary addresses on the same interface unit, and all existing addresses remain unchanged after commit. This precisely matches the engineer's requirement.

The 'commit check' command validates the syntax of the candidate configuration.

'commit check' parses and validates the candidate configuration against the schema without loading it into the running configuration, reporting syntax or semantic errors. This satisfies the stem's requirement for a statement about commit command behaviour on Junos devices.

The 'commit synchronize' command is used on a dual-RE system to commit on both REs.

On dual Routing Engine systems, 'commit synchronize' commits the candidate configuration on both the master and backup REs simultaneously, keeping them consistent. This satisfies the stem's requirement by correctly describing synchronised commit behaviour across redundant control planes.

The 'commit confirmed 5' command will roll back the configuration after 5 minutes if not confirmed.

'commit confirmed 5' activates the candidate configuration but automatically rolls it back after five minutes unless the administrator issues a confirming commit. This satisfies the stem by correctly describing the safety mechanism that prevents locking out remote management access.

Both the interface address and security policy will be activated.

The commit command in Junos atomically activates all changes in the candidate configuration, including both the interface address and the security policy. There is no separate commit process or reboot needed for security policies, so both changes take effect simultaneously. The validation performed during commit confirms that the configuration is syntactically correct, and since the exhibit shows no errors, both changes will be applied.

show snmp

The 'show snmp' command is the correct diagnostic tool on Junos devices for verifying SNMP configuration and operation. It displays whether the SNMP agent is enabled, configured trap groups, target addresses, community strings, and various SNMP statistics. This command directly shows why a device might not send traps, such as missing trap-group definitions, incorrect targets, or an explicitly disabled SNMP service.

show system processes extensive

The `show system processes extensive` command is the correct diagnostic tool because it provides a detailed snapshot of every running process on the Junos device, including their IDs, CPU utilization percentages, and the cumulative time spent in user and system mode. The `extensive` keyword adds thread-level details and memory usage, enabling an administrator to pinpoint exactly which process is driving the high CPU load, such as rpd or mgd. This directly addresses the troubleshooting scenario.

request support information

This is a Junos operational command that automatically collects a comprehensive set of system data, including configurations, interface statistics, routing tables, logs, system processes, and other diagnostic information into a single archive. It is designed specifically for troubleshooting and for providing a complete snapshot to Juniper support or for offline analysis. This one command aggregates far more data than any individual show command, making it the correct choice for a full system snapshot.

request system reboot at 03:00

The `request system reboot at 03:00` command schedules the reboot to occur at 03:00 in the device's local time zone. Junos validates the time argument and queues the reboot, allowing the engineer to finish maintenance tasks before the device restarts. This is the exact operational command designed for a scheduled reboot at a specific time.

A faulty transceiver

A faulty transceiver (SFP/SFP+/QSFP) is a classic source of receive-side errors: imperfect optical transmission or receiver degradation creates bit errors, FCS/CRC failures, and symbol errors that increment the input error counter. On Junos, an optics failure can appear intermittently as temperature or wavelength drifts, making it a prime suspect for sporadic packet loss with input errors. Swapping the optic is the standard first step to confirm.

show system commit

show system commit is correct because it directly displays the commit log, which records every configuration commit along with the timestamp, user, and commit comment. By listing each commit event, it provides the exact last time the configuration was changed and saved as an active operational state. This command is the standard way to audit configuration change history on Junos devices.

show route

The 'show route' command is the correct tool for troubleshooting a connectivity issue because it displays the active routing table, including all routes learned from each routing protocol, with their next-hop addresses and preference values. It allows an engineer to verify whether a destination is reachable, which route is being used, and why that route was selected. This command directly answers whether the router has a valid forwarding path to the target network.

Configure two static default routes with equal metric values and enable ECMP.

In Junos, two static default routes with equal metrics have the same preference and are both installed in the routing table as equal-cost paths. To actually balance traffic, you must enable ECMP, typically by configuring 'load-balance per-packet' in the forwarding options or a policy statement. This allows Junos to distribute flows across both ISPs while maintaining per-flow consistency, which is essential for TCP sessions.

The static route, because it has a lower preference value.

Junos routes are selected by comparing the preference values from different protocols, and the route with the lowest preference is installed as active in the forwarding table. Static routes have a default preference of 5, while OSPF internal routes use 10, so the static route is chosen. This lower preference value reflects that static routes are manually configured and therefore considered the most reliable and predictable source for that destination.

Direct routes

The direct route is automatically installed by Junos when you assign an IP address to an interface and it is operational. It represents the subnet directly attached to that interface, and its existence does not involve any routing protocol at all. This is why it is classified as protocol-independent.

Local routes

A local route is the /32 route that Junos automatically creates for the interface's own IP address, used to route traffic destined to the router. Like the direct route, it is generated purely from interface configuration and requires no dynamic protocol to be running. It is therefore protocol-independent.

Static routes

Static routes are explicitly configured by an administrator using the Junos CLI, for example with 'set routing-options static route'. They do not rely on any dynamic routing protocol to be learned or maintained, and they remain in the routing table until removed or the next hop becomes unavailable. Thus, they are considered protocol-independent routes.

The OSPF route because it is marked with an asterisk.

The asterisk in the routing table marks the active route installed in the forwarding table. Junos selects the OSPF route for 192.168.1.0/24 because it has the lowest preference value compared with competing protocols, satisfying the stem's requirement to identify which route is actually active.

Use a routing policy to increase the preference of the OSPF route from Router B.

Using a routing policy to increase the preference of the OSPF route from Router B makes that route less desirable in the Junos routing table. Since Junos selects the route with the lowest preference value, raising Router B's preference (say, from the default 10 to 15) leaves Router A's default OSPF route as the active path. This allows you to influence the active route selection centrally on the local router without changing OSPF metrics or filtering prefixes.

The VLANs are not defined on the switch.

For inter-VLAN routing to work in Junos, each VLAN must first be defined under the [edit vlans] hierarchy so the switch knows which VLAN ID or name to associate with the ports and IRB interface. Without that definition, the IRB interface cannot be logically bound to a broadcast domain, and traffic cannot be forwarded between the two VLAN subnets. The stem confirms the IRB has an IP address, but if the VLANs themselves are not configured, the switch has no way to match incoming frames to a routing instance. This missing VLAN definition is exactly what breaks the traffic flow, making this the correct answer.

The MTU on the interface is mismatched.

An MTU mismatch is a classic cause of OSPF adjacency being stuck in the EXSTART state. During the Database Description (DD) packet exchange, OSPF embeds the interface MTU in the DD header. If one interface has a larger MTU and sends a DD packet that exceeds the neighbor's MTU, the receiving router will drop the packet. Since the neighbor never receives the DD packet, the routers cannot complete the master/slave negotiation, and the adjacency remains permanently in EXSTART rather than progressing to FULL.

It determines the master router election.

The priority value in VRRP is the primary criterion for master router election; the router with the highest priority becomes the master for the virtual router group. If two routers advertise the same priority, the one with the higher primary IP address wins the election. Thus, a higher priority makes a device more likely to be chosen as master, either through initial election or by preempting a lower-priority active master when preemption is enabled.

show interfaces extensive

The 'show interfaces extensive' command is essential because it reveals the actual data-link encapsulation currently in use on the interface, along with detailed physical and protocol state information. This allows the engineer to confirm whether both routers are configured with matching encapsulation types (e.g., PPP, HDLC, or Frame Relay). It also provides error counters and keepalive statistics, which can expose framing mismatches or negotiation failures. Without this operational view, a layer-1 connectivity issue could be mistakenly attributed to configuration when the real cause is an encapsulation mismatch.

Default route pointing to the gateway

A default route (0.0.0.0/0) is the least-specific route and matches all packets whose destination has no other matching entry in the routing table. In Junos, configuring a static default route with next-hop pointing to the gateway is the standard way to give a server off-subnet reachability. This is exactly what a default gateway does for a host.

The route with metric 5 is installed

When two static routes share the same preference, Junos treats the lower metric as the better path. The metric-5 route therefore wins the route selection and is installed in the forwarding table; metric 10 remains inactive.

commit

The `commit` command is the only way to make candidate configuration changes active and permanent in Junos. It runs full configuration validation and, if successful, installs the candidate into the active configuration store, which is what loads at reboot. Because `commit` persists the changes to storage and activates them at once, it is the required final step after editing any configuration.

rollback 0

The correct way to quickly discard all uncommitted changes in the candidate configuration is to execute 'rollback 0' in configuration mode. This operation overwrites the candidate configuration with the contents of the most recent committed configuration, effectively resetting any modifications made since the last commit. It is the fastest method because it does not require a reboot or additional file operations, and you can verify the change by entering 'show configuration' to confirm the candidate now matches the active configuration.

traceroute

traceroute is the correct tool because it actively probes the network path by sending packets with incrementally increasing TTL values, then collects the ICMP TTL-exceeded messages sent back by each router in turn. This reveals the sequence of IP addresses of every hop along the route to the destination, along with round-trip times for each hop, thus mapping the actual forwarding path hop by hop.

show configuration

`show configuration` is the correct Junos command to view the active configuration. In operational mode, it displays the candidate configuration, which reflects the currently committed active configuration plus any uncommitted changes; if no edits are pending, it shows the committed configuration verbatim. The command outputs the entire configuration hierarchy from the top level and can be filtered or scoped to a specific hierarchy, making it the definitive way to inspect the device's active or candidate configuration.

set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24

This command assigns an IPv4 address to unit 0 on ge-0/0/0, which automatically creates the logical interface and ties the inet address family to it. Once the address is committed, the interface is implicitly enabled and becomes operationally eligible to carry traffic. This is the correct minimal configuration for the task because it provides the required IP details and activates the interface without needing any additional 'enable' statement.

configure; load merge /var/tmp/changes.txt; commit

This sequence correctly applies the configuration changes by merging the contents of changes.txt into the current candidate configuration. The load merge command overlays the file's statements onto the existing configuration, adding new statements and updating existing ones while leaving all unrelated configuration untouched. The commit then activates the candidate configuration, making the changes effective. This is the safest and most precise way to apply an incremental change during a maintenance window, as it avoids deleting any existing configuration.