JN0-106 Networking Fundamentals Practice Test 2 — 15 Questions

Question 1

An engineer is implementing VLAN trunking between two Juniper EX switches. Which statement about native VLANs on a trunk is correct?

Accepted Answer

Untagged frames arriving on a trunk port are assigned to the native VLAN.. On Juniper EX switches, a trunk port can accept both tagged and untagged frames. Untagged frames received on a trunk port are automatically assigned to the native VLAN, which by default is VLAN 1. This behavior is defined by the IEEE 802.1Q standard, where the native VLAN is the only VLAN that can carry untagged traffic on a trunk link.

Answer

The native VLAN cannot be changed after initial configuration.

Answer

Frames in the native VLAN are always tagged with the VLAN ID on the trunk.

Answer

The native VLAN must be the same as the management VLAN.

Question 2

A network administrator is implementing OSPF on a Juniper MX router. During verification, the OSPF adjacency does not come up. The interfaces have correct IP addresses and are up. What is the most likely cause?

Accepted Answer

The interface MTU does not match between the two routers.. In OSPF, the interface MTU must match between neighbors for the adjacency to form. When a router receives a Database Description (DBD) packet with the 'More' bit set but the packet size exceeds the receiving interface's MTU, the packet is silently dropped, preventing the adjacency from progressing beyond the ExStart state. This is a common issue on Juniper MX routers when connecting to devices with different MTU configurations.

Answer

The router ID is not in the same subnet as the interface.

Answer

The VLAN tag is missing on the interface.

Answer

The max-lsa limit has been reached.

Question 3

Which TWO statements about VLANs are correct? (Choose two.)

Accepted Answer

Trunk links can carry traffic for multiple VLANs.. Trunk links, such as 802.1Q trunk ports, are designed to carry traffic for multiple VLANs by adding VLAN tags to Ethernet frames. This allows a single physical link between switches or between a switch and a router to transport frames from different VLANs simultaneously.

Answer

MAC addresses are shared across VLANs.

Answer

Each VLAN must be assigned a unique IP subnet.

Answer

A single switch port can belong to only one VLAN.

Question 4

Which THREE factors influence OSPF neighbor adjacency formation? (Choose three.)

Accepted Answer

Area ID. OSPF neighbor adjacency formation requires that both routers agree on several parameters. Among these are the Area ID (must match), Hello and dead intervals (must match), and MTU (must match). If any of these differ, the adjacency will not form. Router ID must be unique per router but not identical between neighbors. Authentication settings are optional and, if configured, must also match.

Answer

Router ID

Answer

Authentication settings

Question 5

Which THREE are valid methods to reduce spanning-tree convergence time? (Choose three.)

Accepted Answer

Enabling loop guard on root ports. Loop guard prevents alternate or root ports from becoming designated in the event of a BPDU loss, which avoids loops and the need for STP reconvergence. By stabilizing the port state, it indirectly reduces convergence time by preventing unnecessary topology changes.

Answer

Increasing the forward-delay timer

Answer

Enabling MAC address notification

Question 6

Refer to the exhibit. An engineer adds a new static route to 10.10.10.0/24 via next-hop 172.16.1.2. The new route does not appear in the route table. What is the most likely reason?

Accepted Answer

The next-hop 172.16.1.2 is not directly reachable.. In Junos, a static route's next-hop must be directly reachable (i.e., on a connected subnet) for the route to be installed in the inet.0 route table. If the next-hop 172.16.1.2 is not directly connected, the route remains hidden (inactive) and does not appear in the forwarding table. Junos does not perform recursive next-hop resolution for static routes by default unless configured with 'resolve'.

Answer

The route requires an export policy to be installed.

Answer

The route has a different AS path.

Answer

Static routes cannot have the same preference as an existing route.

Question 7

Which TWO statements about IPv4 addressing are correct?

Accepted Answer

The network 169.254.0.0/16 is used for link-local addressing.. Options B and E are correct. 169.254.0.0/16 is reserved for link-local addressing (APIPA), and 127.0.0.1 is the loopback address. Option A is false because a /24 subnet mask provides 254 usable host addresses (2^8 - 2), not 256. Option C is false because 192.168.0.0/16 is a private address range. Option D is false because 10.0.0.0/8 is also private.

Answer

A /24 subnet mask provides 256 usable host addresses.

Answer

The address 192.168.0.0/16 is a public address.

Answer

The address 10.0.0.0/8 is a public address.

Question 8

Refer to the exhibit. The administrator has verified that the remote router's interface uses PPP encapsulation. What is the most likely cause of the link not passing traffic?

Accepted Answer

The encapsulation type is mismatched.. The exhibit shows the local interface is configured with HDLC encapsulation, while the remote uses PPP. This encapsulation mismatch prevents Layer 2 communication. Option A is incorrect because a speed mismatch would cause physical layer errors but the link is typically up, and the encapsulation mismatch is the most direct cause given the PPP verification. Option C is incorrect because a wrong IP address would still allow Layer 2 connectivity but prevent Layer 3 routing, while the issue is at Layer 2. Option D is incorrect because an administratively down interface would not establish a link, but the scenario describes a link that is up but not passing traffic.

Answer

The interface has a speed mismatch.

Answer

The interface is using the wrong IP address.

Answer

The interface is administratively down.

Question 9

A medium-sized enterprise has its headquarters (HQ) and a remote branch office connected via a dedicated point-to-point link. The HQ router (Juniper MX) has interface ge-0/0/1 with IP 10.0.0.1/30 connected to the branch router (Juniper SRX) interface ge-0/0/0 with IP 10.0.0.2/30. The branch LAN is 192.168.2.0/24, and the HQ LAN is 10.0.1.0/24. The branch router has a default route pointing to 10.0.0.1. The HQ router has a static route for 192.168.2.0/24 with next-hop 10.0.0.2, but it was recently changed incorrectly to point to 10.0.0.10 due to a configuration error. Users at the branch report that they can access the internet via the HQ router but cannot reach the HQ LAN's file server at 10.0.1.100. From the HQ router, you can ping the branch router's interface IP (10.0.0.2) successfully, but you cannot ping any device in the branch LAN (192.168.2.0/24). You check the routing table on the HQ router and see that the static route for 192.168.2.0/24 points to 10.0.0.10. What is the most appropriate corrective action?

Accepted Answer

Change the static route on the HQ router to point to 10.0.0.2.. The static route on the HQ router for 192.168.2.0/24 incorrectly points to 10.0.0.10, which is not a valid next-hop. This prevents traffic from reaching the branch LAN. Changing the next-hop to 10.0.0.2 (the branch router's interface IP) restores connectivity. Option A is unnecessary because the branch router already has a default route covering the HQ LAN. Option B would remove the static route, breaking connectivity to the branch LAN entirely. Option C (proxy ARP) does not correct a misconfigured static route in the routing table.

Answer

Add a static route on the branch router for 10.0.1.0/24 pointing to 10.0.0.1.

Answer

Remove the static route and rely on the default route on the branch router.

Answer

Enable proxy ARP on the HQ router's ge-0/0/1 interface.

Question 10

A network administrator notices that traffic between two VLANs is not reaching its destination. The switch has an IRB interface configured with an IP address in each VLAN's subnet. What is the most likely missing configuration?

Accepted Answer

The VLANs are not defined on the switch.. The IRB interface provides Layer 3 routing between VLANs, but it requires the VLANs themselves to be defined on the switch. If the VLANs are not defined, the switch cannot associate the IRB interface with the correct broadcast domains, and traffic will not be forwarded between them. Option C correctly identifies this missing configuration.

Answer

The IRB interface does not have an IP address configured.

Answer

The VLANs are on different switches.

Answer

The switch ports are not configured for VLAN tagging.

Question 11

A network engineer is troubleshooting OSPF adjacencies between two Juniper routers. The routers are directly connected and have matching OSPF configurations except for the router IDs. Router A has router-id 10.0.0.1, Router B has router-id 10.0.0.2. The adjacency remains in the EXSTART state. What is the most likely cause?

Accepted Answer

The MTU on the interface is mismatched.. The EXSTART state indicates that the routers have progressed past the 2-Way state and are attempting to exchange Database Description (DBD) packets. A common cause for getting stuck in EXSTART is an MTU mismatch, because OSPF uses the interface MTU to determine the maximum size of DBD packets. If Router A's MTU is larger than Router B's, Router B will drop the oversized DBD packet and the adjacency will remain in EXSTART.

Answer

The router IDs are not the same.

Answer

The area ID is not configured.

Answer

The hello and dead intervals are mismatched.

Question 12

You are responsible for a Juniper MX router that connects two customer sites over a Layer 3 VPN. The router is configured with BGP for VPN routes and uses MPLS to forward traffic. Recently, the customer reported that traffic from Site A (10.0.1.0/24) to Site B (10.0.2.0/24) is intermittently failing. You check the routing table on the router and see that both routes are present with valid next-hops. However, when you ping from the router's loopback to the remote site's loopback, the ping succeeds. MPLS labels are being assigned and the LSP is up. You also notice that when the failure occurs, the router's BGP session to the remote PE is still established. The failure seems random and lasts a few seconds before recovering. Which troubleshooting step is most likely to identify the root cause?

Accepted Answer

Review the forwarding table for the affected prefixes and check for any discrepancies.. The issue is intermittent packet loss with valid routes in the routing table but successful pings from the loopback. This points to a forwarding table (FIB) inconsistency, where the control plane (routing table) has the correct next-hop, but the forwarding plane (PFE) may have a stale or incorrect entry for the specific prefixes. Checking the forwarding table with 'show route forwarding-table' will reveal if the next-hop or label information differs from the routing table, which is a classic symptom of a hardware programming issue or a transient PFE problem.

Answer

Check the interface error counters for CRC errors or drops.

Answer

Verify the BGP session state and check for route flapping.

Answer

Check the MPLS label switching table to ensure labels are correctly assigned.

Question 13

A network engineer is troubleshooting connectivity between two directly connected Juniper routers. The interface on Router A shows 'up' but no packets are being received from Router B. Which command should the engineer use on Router A to check if the interface is expecting to receive a specific encapsulation type?

Accepted Answer

show interfaces extensive. The 'show interfaces extensive' command displays detailed interface information, including the encapsulation type configured on the interface. If Router A expects a specific encapsulation (e.g., PPP, HDLC, or Ethernet) that does not match what Router B is sending, the interface will show 'up' but will not receive packets. This command allows the engineer to verify the configured encapsulation type. Option B is incorrect because 'show interfaces terse' provides a concise summary (name, status, protocol, and address) but does not include encapsulation details.

Answer

show interfaces terse

Answer

show configuration interfaces

Answer

monitor traffic interface

Question 14

A network administrator is configuring a new subnet for servers that must not communicate with each other directly but must be able to reach a default gateway. Which type of route should be configured on the servers?

Accepted Answer

Default route pointing to the gateway. A default route (0.0.0.0/0) pointing to the gateway is correct because it allows servers to reach any external destination (including the gateway) without requiring explicit routes to each other. Since the servers must not communicate directly, they should not have routes to each other's subnets; the default route ensures all non-local traffic is forwarded to the gateway, which can then enforce isolation policies.

Answer

Host route for the gateway

Answer

Dynamic route via OSPF

Answer

Static route to each other server

Question 15

A Juniper router is configured with two static routes to the same destination network, both with the same preference. One route has a metric of 5, the other a metric of 10. Which route will be installed in the routing table?

Accepted Answer

The route with metric 5 is installed. In JUNOS, when multiple static routes to the same destination have the same preference (administrative distance), the route with the lower metric is selected for installation in the routing table. Here, metric 5 is lower than metric 10, so the route with metric 5 is installed. This behavior follows the standard route selection process where preference is evaluated first, then metric (also called cost or next-hop metric) as a tiebreaker.

Answer

Neither route is installed because they conflict

Answer

The route with metric 10 is installed

Answer

Both routes are installed with equal preference