Networking Fundamentals

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?

Question 3hardmultiple 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?

Question 4easymultiple 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?

Question 5mediummultiple 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?

Question 6hardmulti select

Open the full BGP breakdown →

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

Question 7hardmultiple 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?

Question 8mediummultiple 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?

Question 9easymultiple 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?

Question 10hardmultiple 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?

Question 11mediummultiple choice

Read the full VPN explanation →

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?

Question 12mediumdrag 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 13mediummatching

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 14easymultiple 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?

Question 15easymultiple 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?

Question 16mediummultiple 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?

Question 17mediummultiple 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?

Question 18hardmultiple choice

Open the full STP breakdown →

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?

Question 19hardmultiple 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?

Question 20easymultiple 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?

Question 21mediummultiple choice

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

Question 22hardmultiple choice

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?

Question 23easymulti select

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

Question 24mediummulti select

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

Question 25hardmulti select

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

Question 26easymultiple choice

Refer to the exhibit. A frame with destination MAC 00:0c:29:2a:3b:4d arrives on interface ge-0/0/0. What action will the switch take?

Exhibit

MAC address table:
VLAN        MAC address       Type         Age   Interfaces
default     00:00:5e:00:01:01 Static       -     ge-0/0/0.0
vlan10      00:0c:29:2a:3b:4c Dynamic      20    ge-0/0/1.0
vlan10      00:0c:29:2a:3b:4d Dynamic      10    ge-0/0/2.0
vlan20      00:0c:29:2a:3b:4e Dynamic       5    ge-0/0/3.0

Question 27mediummultiple choice

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

Exhibit

inet.0: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0          *[Static/5] 00:00:01 > to 10.0.0.1 via ge-0/0/0.0
10.0.0.0/8         *[Direct/0] 00:00:01 > via ge-0/0/0.0
10.0.0.1/32        *[Local/0] 00:00:01 Local via ge-0/0/0.0
192.168.1.0/24     *[Static/5] 00:00:01 > to 10.0.0.2 via ge-0/0/0.0

Question 28hardmultiple choice

Refer to the exhibit. The OSPF neighbor adjacency repeatedly goes up and down on R1. What is a likely cause?

Exhibit

Mar 15 10:00:00 R1 rpd[2345]: RPD_OSPF_NBRDOWN: OSPF neighbor 10.0.0.2 (ge-0/0/0) state changed from Full to Down (event: KillNbr)
Mar 15 10:00:01 R1 rpd[2345]: RPD_OSPF_NBRUP: OSPF neighbor 10.0.0.2 (ge-0/0/0) state changed from Down to Full

Question 29easymultiple choice

An engineer is troubleshooting a network issue where hosts on the same VLAN cannot communicate with each other. Which configuration element is most likely missing?

Question 30easymultiple choice

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

Question 31mediummultiple choice

Full Practice Test →All Objectives

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?

More Networking Fundamentals questions available in the full practice test.

Continue Practising →

All JNCIA-JUNOS Objectives

Objective 1.0

Networking Fundamentals

JNCIA-JUNOS Practice Questions

What this objective tests

JNCIA-JUNOS Networking Fundamentals — Key Topics

Networking Fundamentals questions on this certification test your ability to deploy and manage networking fundamentals concepts in scenario-based situations.

Core Networking Fundamentals concepts and how they apply in real-world cloud scenarios.
How to deploy networking fundamentals correctly and verify the outcome.
Troubleshooting networking fundamentals issues by interpreting error output and system state.
Cloud best practices and Networking Fundamentals design trade-offs tested by this certification.

Common exam traps

Where candidates lose marks on Networking Fundamentals

⚠Selecting the most expensive service when a simpler managed option meets the requirement.
⚠Forgetting that cloud resources must be explicitly secured — defaults are rarely secure.
⚠Choosing a global service fix when the issue is region-specific.
⚠Overlooking cost implications of cross-region data transfer in architecture questions.

JNCIA-JUNOS Networking Fundamentals — Practice Questions

30 questions from this objective

Question 2mediummultiple choice

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?

Question 3hardmultiple 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?

Question 4easymultiple 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?

Question 5mediummultiple 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?

Question 6hardmulti select

Open the full BGP breakdown →

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

Question 7hardmultiple 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?

Question 8mediummultiple 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?

Question 9easymultiple 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?

Question 10hardmultiple 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?

Question 11mediummultiple choice

Read the full VPN explanation →

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?

Question 12mediumdrag 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 13mediummatching

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 14easymultiple 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?

Question 15easymultiple 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?

Question 16mediummultiple 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?

Question 17mediummultiple 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?

Question 18hardmultiple choice

Open the full STP breakdown →

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?

Question 19hardmultiple 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?

Question 20easymultiple 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?

Question 21mediummultiple choice

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

Question 22hardmultiple choice

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?

Question 23easymulti select

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

Question 24mediummulti select

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

Question 25hardmulti select

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

Question 26easymultiple choice

Refer to the exhibit. A frame with destination MAC 00:0c:29:2a:3b:4d arrives on interface ge-0/0/0. What action will the switch take?

Exhibit

MAC address table:
VLAN        MAC address       Type         Age   Interfaces
default     00:00:5e:00:01:01 Static       -     ge-0/0/0.0
vlan10      00:0c:29:2a:3b:4c Dynamic      20    ge-0/0/1.0
vlan10      00:0c:29:2a:3b:4d Dynamic      10    ge-0/0/2.0
vlan20      00:0c:29:2a:3b:4e Dynamic       5    ge-0/0/3.0

Question 27mediummultiple choice

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

Exhibit

inet.0: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0          *[Static/5] 00:00:01 > to 10.0.0.1 via ge-0/0/0.0
10.0.0.0/8         *[Direct/0] 00:00:01 > via ge-0/0/0.0
10.0.0.1/32        *[Local/0] 00:00:01 Local via ge-0/0/0.0
192.168.1.0/24     *[Static/5] 00:00:01 > to 10.0.0.2 via ge-0/0/0.0

Question 28hardmultiple choice

Refer to the exhibit. The OSPF neighbor adjacency repeatedly goes up and down on R1. What is a likely cause?

Exhibit

Mar 15 10:00:00 R1 rpd[2345]: RPD_OSPF_NBRDOWN: OSPF neighbor 10.0.0.2 (ge-0/0/0) state changed from Full to Down (event: KillNbr)
Mar 15 10:00:01 R1 rpd[2345]: RPD_OSPF_NBRUP: OSPF neighbor 10.0.0.2 (ge-0/0/0) state changed from Down to Full

Question 29easymultiple choice

An engineer is troubleshooting a network issue where hosts on the same VLAN cannot communicate with each other. Which configuration element is most likely missing?

Question 30easymultiple choice

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

Question 31mediummultiple choice