JN0-106 Exam Questions and Answers

monitor start messages

Displays real-time log messages.

show route receive-protocol bgp 192.0.2.1

show route receive-protocol bgp 192.0.2.1 shows the exact updates received from that specific neighbor before they pass through the routing table, including the import-policy decision. The output marks each prefix with an 'A' (accept) or 'I' (ignore/reject) and, when rejected, prints the policy name and reason. This makes it the right diagnostic for verifying why a route from 192.0.2.1 was not installed, because it exposes the BGP input policy evaluation on every received prefix.

show interfaces terse

Correct — 'show interfaces terse' displays a single-line-per-interface summary with columns for Interface, Admin, Link, Proto, and Local address, covering both physical and logical interfaces. It explicitly shows administratively disabled interfaces with an 'admin-down' flag, while also indicating the actual operational link state ('up' or 'down'). This makes it the most efficient command for quickly surveying the operational status of all interfaces on a Junos device.

The interface ge-0/0/0 is missing the 'host-inbound-traffic' configuration under its security zone; you should add the appropriate system services under the zone.

This is the most likely cause because the device cannot initiate traffic without explicit host-inbound traffic settings.

set protocols ospf area 0 interface ge-0/0/1 metric 200

This is the correct configuration because in JUNOS, OSPF interface metric is explicitly set with the `metric` statement under `protocols ospf` for the specific interface. By assigning a metric of 200 to ge-0/0/1, the router's OSPF cost calculation makes that interface significantly more expensive than ge-0/0/0 (which retains the default metric, typically 10 for Ethernet), thereby forcing transit traffic to prefer ge-0/0/0. This effectively shifts traffic away from ge-0/0/1 while still allowing the OSPF adjacency to remain established, so the link stays available for redundancy or less-preferred use.

Emergency messages are logged to all destinations.

Emergency messages are indeed logged to all destinations because each configured syslog target has a severity threshold that includes 'emerg'. The console's 'any warning' means it logs warning and everything more severe (emerg, alert, crit, err), the file 'messages' with 'any any' logs every severity including emerg, and the remote host with 'any critical' logs critical and above, which again includes emerg. Since all thresholds capture severity level 0, every destination receives emergency messages, making this the correct statement.

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.

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

Correct.

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

Correct.

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

Correct.

The firewall filter applied to the loopback interface is shared across all routing instances; use a separate interface for management traffic or apply the filter only to the 'internet' instance's logical system.

The loopback interface is shared; the filter affects all traffic to the loopback.

Configuration groups are defined under the [edit groups] hierarchy.

Configuration groups are indeed defined under the 'groups' hierarchy and can be inherited.

The 'apply-groups' statement is used to include a group's configuration at a specific hierarchy level.

'apply-groups' is used to apply a group's configuration at the desired hierarchy level.

commit

The 'commit' command permanently activates the candidate configuration by copying it into the active configuration and applying it to the routing and forwarding planes. It also writes the configuration to non-volatile storage (e.g., flash), ensuring it survives a reboot or power cycle. This is the standard, definitive way to make configuration changes persistent in Junos.

Use the 'rollback rescue' command.

The 'rollback rescue' command loads the previously saved rescue configuration from the rescue area into the candidate configuration. This is the correct restore mechanism because it explicitly retrieves the snapshot created via 'request system configuration rescue save'. The command does not automatically commit the change; the engineer must still run 'commit' to apply the rescued configuration to the active Janos configuration.

On RE1: request system software add jinstall-20.2R2.tgz reboot; after reboot, on RE0: request chassis routing-engine master switch; then request system software add jinstall-20.2R2.tgz reboot

Minimizes downtime by upgrading backup first, then switching.

Replace the cable with a known good one because CRC and frame errors indicate a physical layer problem such as a damaged cable or loose connector.

CRC and frame errors indicate that frames are receiving an invalid FCS, which is a classic symptom of a physical-layer issue such as a damaged cable, loose connector, or excessive signal attenuation. The problem appeared after a recent cable change, which strongly implicates the new cable or its seating. Replacing that cable with a known-good one is the correct first step because it directly tests the most likely failure point, and a clean interface afterward confirms the diagnosis.

Interface state change

An interface state change (up or down) is a primary trigger for routing table updates. When an interface transitions, the kernel notifies rpd, which immediately adds or removes the directly connected route for that subnet; this change in turn causes the routing table to recalculate and, if necessary, sends updated route information to dynamic routing protocols like OSPF or IS-IS.

BGP neighbor reset

Resetting a BGP neighbor—whether a hard reset or a soft reset—forces the BGP session to be torn down or refreshed. The neighbor withdraws all previously advertised routes and then re-advertises them (for a hard reset, via a full session re-establishment), causing the routing table to be emptied and repopulated with those BGP routes, often leading to brief route churn and traffic loss.

show system uptime

The `show system uptime` command is the correct way to view CPU load averages on Junos because its output begins with a `Load averages:` line that shows the 1-, 5-, and 15-minute averages. These three numbers indicate how many threads are runnable or waiting for I/O, providing a historical trend that a simple percentage cannot capture. The command also shows system uptime, time, and active users, but the load average is the key field for this question.

Run 'request system storage cleanup'

The 'request system storage cleanup' command is the correct method because it systematically scans well-known system directories and removes only files that are safe to delete, such as stale core files, old log files, and unused software images, while preserving the current system's operational logs and active configuration. It reports how much space was reclaimed and is designed by Juniper to be the standard, nondestructive way to free the /var partition. This avoids the pitfalls of ad-hoc deletion and ensures essential diagnostic data remains intact.

Use 'request system software add <image> re1' and then 'request system reboot re1'

Targeting re1 with the 're1' keyword ensures the image is installed only on the backup Routing Engine, leaving the active primary RE untouched. Rebooting re1 restarts only that RE; the primary continues handling forwarding and control traffic, so there is no service interruption. After re1 returns online as standby, it is ready to assume primary role in a later switchover, which is the correct maintenance procedure.

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.

One of the static routes resolves to multiple next hops, causing imbalance.

If one route resolves to multiple next hops, it may appear as multiple routes, skewing load balancing.

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 route with preference 10.

Preference is the primary selection criterion.

Configure the static default route with a preference of 180 so that the BGP default routes (pref 170) are preferred when available.

This ensures BGP default is used when up, and OSPF routes to R2's default become active when R1's BGP is down.

First configure match conditions, then configure the action, and finally apply the filter to the interface.

This is correct because you must define what traffic to match (from clause) and what action to take (then clause) before applying the filter to an interface. Applying the filter without a complete term would result in an incomplete configuration.

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.

Review the forwarding table for the affected prefixes and check for any discrepancies.

The forwarding table may have stale entries or incorrect label operations causing intermittent forwarding failures.

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

Lower metric is preferred when preference is equal.

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.

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.

Routing protocol adjacencies will be lost, causing routing instability.

The rpd (Routing Protocol Daemon) is the sole software process managing all dynamic routing protocols, including OSPF, BGP, and IS-IS. When it is killed, every established adjacency immediately tears down, causing neighboring routers to mark the node unreachable and recalculate paths. This produces route flap and forwarding loops until rpd restarts and rebuilds sessions, so the primary impact is severe routing instability.

ping <external website FQDN>

When you execute 'ping <external website FQDN>' on Junos, the CLI first resolves the hostname to an IP address using the DNS servers configured under 'system name-server'. A successful resolution is shown directly in the output, where ping reports the target IP before sending ICMP requests. If the DNS query times out or fails, Junos returns a 'unable to resolve hostname' error, making this an effective, one-command DNS resolution test. Note that even if ICMP is blocked by the remote host, the appearance of the IP address in the output already confirms forward DNS works.

The 'commit check' command validates the candidate configuration without activating it.

It checks syntax and semantics without applying.

The commit command activates the candidate configuration.

This is the primary purpose of commit.

The 'commit confirmed' command automatically rolls back if not confirmed within the timeout.

This is the behavior of commit confirmed.

Add a new term at the beginning of the filter that accepts SSH traffic from the management network, then reorder the terms so that this term is evaluated first.

Inserting a new accept term at the top of the filter and committing it ensures that SSH packets sourced from the management network match this term first, before any deny term can be evaluated. Junos first-match semantics guarantee that once the accept action is applied, no later term can override it. Limiting the source to the management network preserves the security boundary and only restores the intended SSH access, rather than allowing SSH from arbitrary sources.