Networking Fundamentals practice questions

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?

Trap 1: The IRB interface does not have an IP address configured.

The stem states the IRB interface has an IP address, so this is not the issue.

Trap 2: The VLANs are on different switches.

Inter-VLAN routing can occur on a single switch; VLANs do not need to be on different switches.

Trap 3: The switch ports are not configured for VLAN tagging.

VLAN tagging is used for trunk ports, not for inter-VLAN routing on a single switch.

A
The IRB interface does not have an IP address configured.
Why wrong: The stem states the IRB interface has an IP address, so this is not the issue.
B
The VLANs are on different switches.
Why wrong: Inter-VLAN routing can occur on a single switch; VLANs do not need to be on different switches.
C
The VLANs are not defined on the switch.
Without defining the VLANs, the switch cannot associate ports or IRB interfaces with them.
D
The switch ports are not configured for VLAN tagging.
Why wrong: VLAN tagging is used for trunk ports, not for inter-VLAN routing on a single switch.

Review the full OSPF breakdown →

Question 2hardmultiple choice

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?

Trap 1: The router IDs are not the same.

Router IDs must be unique; they do not need to match.

Trap 2: The area ID is not configured.

Mismatched area IDs would prevent adjacency from forming, but the stem says matching configurations.

Trap 3: The hello and dead intervals are mismatched.

Mismatched hello/dead intervals would cause the adjacency to be stuck in INIT or DOWN, not EXSTART.

A
The MTU on the interface is mismatched.
A mismatch in MTU can prevent OSPF from exchanging DD packets, causing the adjacency to remain in EXSTART.
B
The router IDs are not the same.
Why wrong: Router IDs must be unique; they do not need to match.
C
The area ID is not configured.
Why wrong: Mismatched area IDs would prevent adjacency from forming, but the stem says matching configurations.
D
The hello and dead intervals are mismatched.
Why wrong: Mismatched hello/dead intervals would cause the adjacency to be stuck in INIT or DOWN, not EXSTART.

Review the full subnetting walkthrough →

Question 3easymultiple choice

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?

Trap 1: Source address

Source addresses are optional; 'any' can be used to match any source address.

Trap 2: Application

Applications are not mandatory; 'any' can be used to match all applications.

Trap 3: Destination zone

Destination zone is also required, but the question asks for the element needed for the traffic to be permitted; both source and destination zones are required, but the source zone is the first match criteria.

A
Source address
Why wrong: Source addresses are optional; 'any' can be used to match any source address.
B
Application
Why wrong: Applications are not mandatory; 'any' can be used to match all applications.
C
Destination zone
Why wrong: Destination zone is also required, but the question asks for the element needed for the traffic to be permitted; both source and destination zones are required, but the source zone is the first match criteria.
D
Source zone
A security policy must specify a source zone to match incoming traffic.

Review the full routing breakdown →

Question 4mediummultiple choice

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?

Trap 1: It sets the interval for VRRP advertisements.

Advertisement interval is configured separately with the 'advertise-interval' parameter.

Trap 2: It determines the virtual MAC address.

The virtual MAC address is based on the VRRP group ID, not priority.

Trap 3: It changes the virtual IP address.

The virtual IP address is configured directly and is not affected by priority.

A
It sets the interval for VRRP advertisements.
Why wrong: Advertisement interval is configured separately with the 'advertise-interval' parameter.
B
It determines the master router election.
Higher priority increases the chance of becoming the master.
C
It determines the virtual MAC address.
Why wrong: The virtual MAC address is based on the VRRP group ID, not priority.
D
It changes the virtual IP address.
Why wrong: The virtual IP address is configured directly and is not affected by priority.

Review the full routing breakdown →

Question 5hardmulti select

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

Trap 1: Static routes always have a metric of 1.

Static routes do not have a metric by default; metric is used by dynamic protocols.

Trap 2: Static routes are automatically redistributed into OSPF.

Redistribution requires explicit policy configuration.

Trap 3: The default preference for static routes is 170.

170 is the default preference for OSPF external routes, not static routes.

A
The default preference for static routes is 5.
Junos assigns a default preference of 5 to static routes.
B
Static routes always have a metric of 1.
Why wrong: Static routes do not have a metric by default; metric is used by dynamic protocols.
C
Static routes are automatically redistributed into OSPF.
Why wrong: Redistribution requires explicit policy configuration.
D
Static routes can have a next-hop of 'discard'.
The 'discard' next-hop (null0) is a valid next-hop for static routes to drop traffic.
E
The default preference for static routes is 170.
Why wrong: 170 is the default preference for OSPF external routes, not static routes.

Open the full BGP breakdown →

Question 6hardmultiple choice

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?

Trap 1: Check the interface error counters for CRC errors or drops.

Interface errors would likely cause persistent failures, not intermittent.

Trap 2: Verify the BGP session state and check for route flapping.

The BGP session is established and routes are present, so route flapping may not be the cause.

Trap 3: Check the MPLS label switching table to ensure labels are correctly…

The LSP is up and labels are assigned, so this is likely not the issue.

A
Check the interface error counters for CRC errors or drops.
Why wrong: Interface errors would likely cause persistent failures, not intermittent.
B
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.
C
Verify the BGP session state and check for route flapping.
Why wrong: The BGP session is established and routes are present, so route flapping may not be the cause.
D
Check the MPLS label switching table to ensure labels are correctly assigned.
Why wrong: The LSP is up and labels are assigned, so this is likely not the issue.

Review the full routing breakdown →

Question 7mediummultiple choice

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?

Trap 1: show interfaces extensive

Shows detailed interface info but not specifically encapsulation expectation.

Trap 2: show configuration interfaces

Shows configuration, not current encapsulation status.

Trap 3: monitor traffic interface

Captures packets, not encapsulation.

A
show interfaces extensive
Why wrong: Shows detailed interface info but not specifically encapsulation expectation.
B
show interfaces terse
Displays interface status and encapsulation type.
C
show configuration interfaces
Why wrong: Shows configuration, not current encapsulation status.
D
monitor traffic interface
Why wrong: Captures packets, not encapsulation.

Review the full subnetting walkthrough →

Question 8easymultiple choice

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?

Trap 1: Host route for the gateway

Host route is for a single IP, not for reaching all destinations.

Trap 2: Dynamic route via OSPF

Servers typically do not run routing protocols.

Trap 3: Static route to each other server

Unnecessary and would allow direct communication.

A
Host route for the gateway
Why wrong: Host route is for a single IP, not for reaching all destinations.
B
Default route pointing to the gateway
Standard for server default gateway configuration.
C
Dynamic route via OSPF
Why wrong: Servers typically do not run routing protocols.
D
Static route to each other server
Why wrong: Unnecessary and would allow direct communication.

Question 9hardmultiple choice

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?

Trap 1: Ethernet

Ethernet is not used on serial interfaces.

Trap 2: PPP

PPP does not support subinterfaces.

Trap 3: HDLC

HDLC is Cisco proprietary and does not support subinterfaces.

A
Ethernet
Why wrong: Ethernet is not used on serial interfaces.
B
PPP
Why wrong: PPP does not support subinterfaces.
C
Frame Relay
Frame Relay supports subinterfaces for multiple logical circuits.
D
HDLC
Why wrong: HDLC is Cisco proprietary and does not support subinterfaces.

Read the full NAT/PAT explanation →

Question 10mediummultiple choice

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?

Trap 1: Neither route is installed because they conflict

Static routes can coexist; the best is chosen.

Trap 2: The route with metric 10 is installed

Higher metric is worse.

Trap 3: Both routes are installed with equal preference

Only the best route is installed.

A
Neither route is installed because they conflict
Why wrong: Static routes can coexist; the best is chosen.
B
The route with metric 5 is installed
Lower metric is preferred when preference is equal.
C
The route with metric 10 is installed
Why wrong: Higher metric is worse.
D
Both routes are installed with equal preference
Why wrong: Only the best route is installed.

Read the full VPN explanation →

Question 11mediumdrag order

Arrange the steps to configure an IPsec VPN on a Junos SRX in the correct order.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 12mediummatching

Read the full Networking Fundamentals explanation →

Match each Junos system log severity level to its meaning.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

System is unusable

Immediate action needed

Critical conditions

Error conditions

Warning conditions

Question 13easymultiple choice

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?

Trap 1: The hosts are configured with IP addresses in different subnets

Hosts on the same VLAN should be in the same IP subnet; if not, they cannot communicate at Layer 3.

Trap 2: The ARP cache on the hosts is stale

A stale ARP cache would cause a unicast frame to be sent to the wrong MAC, but the MAC table entries would not both be present.

Trap 3: Spanning Tree Protocol is blocking a port

STP blocking would prevent the port from forwarding, but the MAC table would not show that port.

A
The VLAN is not allowed on the trunk between the switches
If the VLAN is not allowed on the trunk, frames are dropped, even though MAC addresses are learned on access ports.
B
The hosts are configured with IP addresses in different subnets
Why wrong: Hosts on the same VLAN should be in the same IP subnet; if not, they cannot communicate at Layer 3.
C
The ARP cache on the hosts is stale
Why wrong: A stale ARP cache would cause a unicast frame to be sent to the wrong MAC, but the MAC table entries would not both be present.
D
Spanning Tree Protocol is blocking a port
Why wrong: STP blocking would prevent the port from forwarding, but the MAC table would not show that port.

Read the full Networking Fundamentals explanation →

Question 14easymultiple choice

A host needs to verify that its assigned IP address is not already in use on the network. Which type of packet does the host send?

Trap 1: ARP reply with its own MAC address

An ARP reply is only sent in response to an ARP request.

Trap 2: Gratuitous ARP reply

A gratuitous ARP reply is sent to update caches, not for duplicate detection.

Trap 3: ARP request with target IP set to the default gateway

This is used to resolve the gateway's MAC address, not for duplicate detection.

A
ARP reply with its own MAC address
Why wrong: An ARP reply is only sent in response to an ARP request.
B
ARP request with target IP set to its own IP
This is the standard method for duplicate address detection, where the host sends an ARP request for its own IP.
C
Gratuitous ARP reply
Why wrong: A gratuitous ARP reply is sent to update caches, not for duplicate detection.
D
ARP request with target IP set to the default gateway
Why wrong: This is used to resolve the gateway's MAC address, not for duplicate detection.

Question 15mediummultiple choice

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?

Trap 1: The VLANs are not configured with the same VLAN ID

VLAN IDs are unique within a switch, but they do not affect routing.

Trap 2: The switch needs an external router configured for VLAN routing

The switch can route between VLANs internally if properly configured.

Trap 3: The IRB interfaces are not in the same routing instance

By default, all IRBs are in the same default routing instance.

A
The VLANs are not configured with the same VLAN ID
Why wrong: VLAN IDs are unique within a switch, but they do not affect routing.
B
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
Inter-VLAN routing requires IP routing to be enabled. The switch forwards between IRBs only if routing is on.
C
The switch needs an external router configured for VLAN routing
Why wrong: The switch can route between VLANs internally if properly configured.
D
The IRB interfaces are not in the same routing instance
Why wrong: By default, all IRBs are in the same default routing instance.

Review the full OSPF breakdown →

Question 16mediummultiple choice

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?

Trap 1: The router drops the packet due to a routing conflict

No conflict; the router will use the route with the longest prefix.

Trap 2: The static route to 10.1.1.0/24

The /24 is less specific than /25, so it does not win.

Trap 3: Both routes are used for load balancing

Load balancing requires equal-cost routes with the same prefix length.

A
The router drops the packet due to a routing conflict
Why wrong: No conflict; the router will use the route with the longest prefix.
B
The OSPF route to 10.1.1.0/25
The /25 is the longest prefix match.
C
The static route to 10.1.1.0/24
Why wrong: The /24 is less specific than /25, so it does not win.
D
Both routes are used for load balancing
Why wrong: Load balancing requires equal-cost routes with the same prefix length.

Question 17hardmultiple choice

A host in VLAN 10 can ping a host in VLAN 20 without a default gateway configured. What feature is likely enabled on the router that interconnects the VLANs?

Trap 1: VLAN translation is configured on the trunk

VLAN translation changes VLAN IDs but does not affect Layer 3 forwarding.

Trap 2: IP routing is enabled on the router

IP routing is necessary but not sufficient; the host needs a gateway or proxy ARP.

Trap 3: Dynamic ARP Inspection

DAI is used to prevent ARP spoofing, not to enable routing without a gateway.

A
VLAN translation is configured on the trunk
Why wrong: VLAN translation changes VLAN IDs but does not affect Layer 3 forwarding.
B
Proxy ARP
Proxy ARP enables the router to reply to ARP requests for addresses in other subnets, making the host think the remote host is on the same subnet.
C
IP routing is enabled on the router
Why wrong: IP routing is necessary but not sufficient; the host needs a gateway or proxy ARP.
D
Dynamic ARP Inspection
Why wrong: DAI is used to prevent ARP spoofing, not to enable routing without a gateway.

Open the full STP breakdown →

Question 18hardmultiple choice

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?

Trap 1: Loop guard

Loop guard prevents alternate ports from becoming designated in case of BPDU loss.

Trap 2: Root guard

Root guard prevents a port from becoming a root port, but does not stop BPDUs.

Trap 3: UplinkFast

UplinkFast is a Cisco proprietary feature for fast convergence.

A
Loop guard
Why wrong: Loop guard prevents alternate ports from becoming designated in case of BPDU loss.
B
BPDU guard
BPDU guard disables the port upon receiving a BPDU, preventing loops on PortFast ports.
C
Root guard
Why wrong: Root guard prevents a port from becoming a root port, but does not stop BPDUs.
D
UplinkFast
Why wrong: UplinkFast is a Cisco proprietary feature for fast convergence.

Read the full NAT/PAT explanation →

Question 19easymultiple choice

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?

Trap 1: It sends the frame back to the source port

The switch does not forward frames back to the source port to prevent loops.

Trap 2: It floods the frame to all ports except the receiving port

Flooding is for unknown unicast, broadcast, or multicast frames.

Trap 3: It drops the frame

Known unicast frames are forwarded, not dropped.

A
It sends the frame back to the source port
Why wrong: The switch does not forward frames back to the source port to prevent loops.
B
It floods the frame to all ports except the receiving port
Why wrong: Flooding is for unknown unicast, broadcast, or multicast frames.
C
It drops the frame
Why wrong: Known unicast frames are forwarded, not dropped.
D
It forwards the frame only out of the port associated with that MAC address
The switch uses the MAC table to forward the frame only to the correct port.

Read the full Networking Fundamentals explanation →

Question 20mediummultiple choice

Which field in an Ethernet frame is used by a switch to learn which source MAC address belongs to which port?

Trap 1: Ethertype field

Ethertype identifies the upper-layer protocol.

Trap 2: Destination MAC address

The destination MAC is used to look up the outgoing port.

Trap 3: VLAN ID field

VLAN ID determines the broadcast domain, not the MAC-to-port mapping.

A
Ethertype field
Why wrong: Ethertype identifies the upper-layer protocol.
B
Destination MAC address
Why wrong: The destination MAC is used to look up the outgoing port.
C
VLAN ID field
Why wrong: VLAN ID determines the broadcast domain, not the MAC-to-port mapping.
D
Source MAC address
The switch learns the source MAC and associates it with the incoming port.