JN0-106 Networking Fundamentals — Timed 20 Questions

Question 1

An administrator needs to ensure that traffic from the 192.168.1.0/24 subnet is allowed to reach the internet through a Juniper SRX firewall. The SRX is configured with security policies. Which policy element is required to permit this traffic?

20 minute time limit — choose an answer to begin.

Accepted Answer

Destination zone. In Juniper SRX, security policies require mandatory configuration of source zone, destination zone, source address, destination address, and application (addresses and application can be set to 'any'). For the described traffic, both the source zone (e.g., trust) and destination zone (e.g., untrust) are required to define the traffic flow. The source address is an additional match condition that can be set to the specific subnet, but it is not optional in the policy definition—it must exist (at minimum as 'any').

Answer

Source address

Answer

Application

Question 2

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 3

Which TWO statements about Juniper's implementation of static routes are correct? (Choose two.)

Accepted Answer

The default preference for static routes is 5.. In Juniper's Junos OS, the default preference (administrative distance) for static routes is 5. This value indicates that static routes are highly trusted, only surpassed by directly connected routes (preference 0). This is a Juniper-specific default, differing from Cisco's default of 1 for static routes.

Answer

Static routes always have a metric of 1.

Answer

Static routes are automatically redistributed into OSPF.

Answer

The default preference for static routes is 170.

Question 4

An engineer is designing a network with two routers connected via a serial link. The link should support multiple logical subinterfaces for different VLANs. Which encapsulation type must be used on the serial interface?

Accepted Answer

Frame Relay. Frame Relay is correct because it supports multiple logical subinterfaces (DLCIs) on a single serial link, allowing different VLANs to be mapped to separate virtual circuits. Unlike PPP or HDLC, Frame Relay inherently provides the ability to create point-to-point or multipoint subinterfaces for Layer 2 segmentation.

Answer

Ethernet

Answer

PPP

Answer

HDLC

Question 5

Match each Junos system log severity level to its meaning.

Accepted Answer

Emergency: System is unusable. Syslog severity levels from highest to lowest: Emergency, Alert, Critical, Error, Warning, Notice, Info, Debug. Common confusions involve swapping Warning and Notice definitions.

Answer

Warning: Normal but significant conditions

Answer

Notice: Warning conditions

Question 6

A network engineer is troubleshooting connectivity between two hosts on the same VLAN connected to different Juniper EX switches. The MAC address table on each switch shows the correct MAC addresses for both hosts, but ping fails. What is the most likely cause?

Accepted Answer

The hosts are configured with IP addresses in different subnets. Since both switches have correctly learned the MAC addresses of both hosts, Layer 2 forwarding across the trunk is working, meaning the VLAN is allowed. The ping failure therefore points to a Layer 3 issue: the hosts are configured with IP addresses in different subnets. They cannot communicate via IP without a router, even though they are on the same VLAN. The correct answer is B.

Answer

The VLAN is not allowed on the trunk between the switches

Answer

The ARP cache on the hosts is stale

Answer

Spanning Tree Protocol is blocking a port

Question 7

A Juniper EX switch has two VLANs configured, each with an IRB interface assigned an IP address. Pings between hosts in different VLANs fail. What is the most likely missing configuration?

Accepted Answer

The IRB interfaces are not in the same routing instance. On a Juniper EX switch, inter-VLAN routing works automatically when IRB interfaces have IP addresses and are in the same routing instance. No global 'IP routing' toggle or default route is required for directly connected subnets. The most likely missing configuration is that the IRB interfaces are in different routing instances, which prevents routing between them because each routing instance has a separate forwarding table.

Answer

The VLANs are not configured with the same VLAN ID

Answer

IP routing is not enabled globally: set routing-options router-id 10.0.0.1; set routing-options rib inet.0 static route 0.0.0.0/0 next-hop 203.0.113.1

Answer

The switch needs an external router configured for VLAN routing

Question 8

Two routers are connected via a point-to-point Ethernet link. They are configured with IP addresses in the same subnet, but OSPF does not form an adjacency. The link is up/up. What is a likely cause?

Accepted Answer

The OSPF hello and dead intervals are mismatched. OSPF requires that Hello and Dead intervals match between neighbors on a point-to-point link to form an adjacency. Even though the link is up/up and IP addresses are in the same subnet, mismatched timers prevent the routers from agreeing on neighbor state, so no adjacency forms.

Answer

The routers are in different OSPF areas

Answer

OSPF authentication is configured on one router but not the other

Answer

The routers have the same router ID

Question 9

Which TWO statements about ARP are correct? (Select two.)

Accepted Answer

ARP request is sent to the broadcast MAC address. An ARP request is sent as a broadcast frame to the destination MAC address FF:FF:FF:FF:FF:FF, ensuring all hosts on the local network segment receive it. This allows the host with the target IP address to respond. Option E is correct because the ARP reply is unicast directly to the requesting host's MAC address, which was learned from the source hardware address field in the ARP request.

Answer

ARP request is sent to a multicast MAC address

Answer

ARP reply is sent to the broadcast MAC address

Answer

ARP is used for both IPv4 and IPv6

Question 10

Which THREE fields are part of an Ethernet frame header? (Select three.)

Accepted Answer

Destination MAC address. The Ethernet frame header is defined by the IEEE 802.3 standard and consists of the Destination MAC address (6 bytes), Source MAC address (6 bytes), and the EtherType field (2 bytes) or Length field. The Destination MAC address is the first field in the header and identifies the intended recipient of the frame on the local network segment. Without it, switches and hosts would not know which device should process the frame.

Answer

VLAN tag (802.1Q)

Answer

Frame Check Sequence (FCS)

Question 11

Which THREE statements are true about VLANs on Juniper EX switches? (Select three.)

Accepted Answer

A single VLAN can extend across multiple switches via trunk ports. VLANs are designed to span multiple switches by using trunk ports that carry traffic for multiple VLANs. On Juniper EX switches, trunk ports (configured with the 'trunk' port mode) allow VLAN-tagged frames to traverse between switches, enabling a single VLAN to extend across a network. This is fundamental to VLAN operation, as it allows devices in the same VLAN to communicate regardless of which switch they are connected to.

Answer

Hosts in different VLANs can communicate without any additional configuration

Answer

VLANs are automatically created when you assign an interface to an untagged VLAN

Question 12

Refer to the exhibit. A packet with destination IP 192.168.1.100 arrives. Which next-hop IP will the router use?

Accepted Answer

10.0.0.2. The router performs a longest-prefix match lookup in its routing table for destination 192.168.1.100. The most specific matching route is 192.168.1.0/25 via next-hop 10.0.0.2, so the router forwards the packet to 10.0.0.2. Option C is correct.

Answer

10.0.0.1

Answer

10.0.0.0

Answer

Directly connected (the packet is sent directly to 192.168.1.100)

Question 13

A network administrator is configuring a new OSPF network. Which statement about OSPF router IDs is correct?

Accepted Answer

Router IDs must be unique across all routers in the OSPF domain.. In OSPF, the router ID must be unique across the entire OSPF domain to ensure proper neighbor adjacency formation and loop-free routing. If two routers share the same router ID, OSPF cannot distinguish between them, leading to adjacency failures and potential routing loops. This uniqueness requirement is specified in RFC 2328.

Answer

If no router ID is configured, the system uses the lowest IP address on an active interface.

Answer

The router ID must be an IP address from a directly connected interface.

Answer

The router ID is automatically derived from the MAC address.

Question 14

A network engineer is designing a redundant network using RSTP. For faster convergence, what is the recommended method to avoid waiting for the forward delay timer?

Accepted Answer

Configure interfaces connected to end hosts as edge ports.. RSTP (Rapid Spanning Tree Protocol, IEEE 802.1w) achieves faster convergence by eliminating the listening and learning states for edge ports. Configuring interfaces connected to end hosts as edge ports allows them to transition directly to the forwarding state without waiting for the forward delay timer (default 15 seconds), because no BPDUs are expected on those ports and no loop can form.

Answer

Manually specify the root bridge and root port.

Answer

Use link aggregation to bundle multiple links.

Answer

Increase the hello timer to speed up BPDU exchange.

Question 15

A company uses a Juniper MX router to connect two branch offices via a point-to-point link. The link is flapping. Which command would you use to check the interface errors on the link?

Accepted Answer

show interfaces ge-0/0/0 extensive. The 'show interfaces ge-0/0/0 extensive' command provides detailed interface statistics, including error counters such as CRC errors, frame errors, and link state transitions. This is the most comprehensive command to diagnose why a point-to-point link is flapping, as it reveals physical-layer issues that cause the interface to go up/down repeatedly.

Answer

show log messages

Answer

show configuration interfaces ge-0/0/0

Answer

show interfaces ge-0/0/0 terse

Question 16

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 17

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 18

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 19

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 20

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