JN0-280 Exam Questions and Answers | Exam-Dumps (Page: 1)

QUESTION: 1

Leaf and spine data centers are used to better accommodate which type of traffic?

north-east
east-west
north-west
south-east

Answer(s): B

Explanation:

In modern data centers, the shift toward leaf-spine architectures is driven by the need to handle increased east-west traffic, which is traffic between servers within the same data center. Unlike traditional hierarchical data center designs, where most traffic was "north-south" (between users and servers), modern applications often involve server-to-server communication (east-west) to enable services like distributed databases, microservices, and virtualized workloads.
Leaf-Spine Architecture:
Leaf Layer: This layer consists of switches that connect directly to servers or end-host devices. These switches serve as the access layer.
Spine Layer: The spine layer comprises high-performance switches that provide interconnectivity between leaf switches. Each leaf switch connects to every spine switch, creating a non-blocking fabric that optimizes traffic flow within the data center.
East-West Traffic Accommodation:
In traditional three-tier architectures (core, aggregation, access), traffic had to traverse multiple layers, leading to bottlenecks when servers communicated with each other. Leaf-spine architectures address this by creating multiple equal-cost paths between leaf switches and the spine. Since each leaf switch connects directly to every spine switch, the architecture facilitates quick, low-latency communication between servers, which is essential for east-west traffic flows.
Juniper's Role:
Juniper Networks provides a range of solutions that optimize for east-west traffic in a leaf-spine architecture, notably through:
QFX Series Switches: Juniper's QFX series switches are designed for the leaf and spine architecture, delivering high throughput, low latency, and scalability to accommodate the traffic demands of modern data centers.
EVPN-VXLAN: Juniper uses EVPN-VXLAN to create a scalable Layer 2 and Layer 3 overlay network across the data center. This overlay helps enhance east-west traffic performance by enabling network segmentation and workload mobility across the entire fabric.
Key Features That Support East-West Traffic:
Equal-Cost Multipath (ECMP): ECMP enables the use of multiple paths between leaf and spine switches, balancing the traffic and preventing any one path from becoming a bottleneck. This is crucial in handling the high volume of east-west traffic. Low Latency: Spine switches are typically high-performance devices that minimize the delay between leaf switches, which improves the efficiency of server-to-server communications. Scalability: As the demand for east-west traffic grows, adding more leaf and spine switches is straightforward, maintaining consistent performance without redesigning the entire network. In summary, the leaf-spine architecture is primarily designed to handle the increase in east-west traffic within data centers, and Juniper provides robust solutions to enable this architecture through its switch platforms and software solutions like EVPN-VXLAN.

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QUESTION: 2

When troubleshooting an OSPF neighborship, you notice that the router stopped at the ExStart state.
What is the cause of this result?

The priority is set to 255.
There is an interval timing mismatch.
There is an area ID mismatch.
There is an MTU mismatch.

Answer(s): D

Explanation:

When an OSPF (Open Shortest Path First) neighborship is stuck in the ExStart state, it usually points to a mismatch in Maximum Transmission Unit (MTU) settings between two routers trying to establish the adjacency. The ExStart state is where OSPF routers negotiate the master-slave relationship and exchange DBD (Database Description) packets.
Step-by-Step Breakdown:
OSPF Neighbor States: OSPF goes through several states to establish an adjacency with a neighbor:
Down: No hello packets have been received.
Init: Hello packets are received, but bidirectional communication isn't confirmed.
2-Way: Bidirectional communication is established.
ExStart: The routers are negotiating who will be the master and who will be the slave, and begin to exchange DBD packets.
Exchange: The routers start exchanging the database information. Loading: The routers process the Link-State Advertisements (LSAs).
Full: The adjacency is fully established.
MTU Mismatch Issue:
During the ExStart state, both OSPF routers must agree on their MTU values. If there is an MTU mismatch between the two routers, OSPF neighbors will fail to move from the ExStart to the Exchange state. The router with the larger MTU setting will not accept DBD packets from the router with a smaller MTU because the packets may exceed the smaller MTU size. In Juniper devices, this behavior can be identified by examining the MTU settings using the show interfaces command and ensuring both routers have matching MTU configurations. To resolve this issue, either match the MTU settings on both routers or configure OSPF to ignore MTU mismatches using the command set protocols ospf ignore-mtu.

Reference:

Junos Command: show ospf neighbor helps diagnose neighbor states. MTU Adjustment: set interfaces <interface-name> mtu <size> can be used to set the MTU values correctly.

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QUESTION: 3

Which statement is correct about aggregate routes?

The default next hop is discard.
The default next hop is readvertise.
The default next hop is resolve.
The default next hop is reject.

Answer(s): D

Explanation:

An aggregate route is a summarized route that is created by combining multiple specific routes into a single, broader route. In Junos OS, when an aggregate route is configured, its default next hop is set to reject.
Step-by-Step explanation.
Aggregate Route:
Aggregate routes are used to reduce the size of routing tables by representing a collection of more specific routes with a single summary route. They help improve routing efficiency and scalability, especially in large networks.
Default Next Hop Behavior:
When you configure an aggregate route in Junos OS, it has a reject next hop by default. The reject next hop means that if a packet matches the aggregate route but there is no more specific route in the routing table for that destination, the packet will be discarded, and an ICMP "destination unreachable" message is sent to the source.
This behavior helps to prevent routing loops and ensures that traffic isn't forwarded to destinations for which there is no valid route.
Modifying Next Hop:
If needed, the next hop behavior of an aggregate route can be changed to discard (which silently drops the packet) or to another specific next hop. However, by default, the next hop is set to reject.

Reference:

Junos Command: set routing-options aggregate route <route> reject to configure an aggregate route with a reject next hop.
Verification: Use show route to verify the presence and behavior of aggregate routes.

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QUESTION: 4

Which Junos OS routing table stores IPv6 addresses?

inet.0
inet0.6
inet.6
inet6.0

Answer(s): D

Explanation:

In Junos OS, routing information is stored in different routing tables depending on the protocol and address family. For IPv6 addresses, the routing table used is inet6.0.
Step-by-Step explanation.
Routing Tables in Junos:
inet.0: This is the primary routing table for IPv4 unicast routes. inet6.0: This is the primary routing table for IPv6 unicast routes. inet.3: This routing table is used for MPLS-related routing. Other routing tables, like inet.1, inet.2, are used for multicast and other specific purposes.
inet6.0 Routing Table:
When IPv6 is enabled on a Juniper router, all the IPv6 routes are stored in the inet6.0 table. This includes both direct routes (connected networks) and learned routes (from dynamic routing protocols like OSPFv3, BGP, etc.).
Verification:
To view IPv6 routes, the command show route table inet6.0 is used. This will display the contents of the IPv6 routing table, showing the network prefixes, next-hop addresses, and protocol information for each route.

Reference:

Junos Command: Use show route table inet6.0 to check IPv6 routing entries. IPv6 Routing: Ensure that the IPv6 protocol is enabled on interfaces and that routing protocols like OSPFv3 or BGP are properly configured for IPv6 traffic handling.

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QUESTION: 5

What is the primary purpose of an IRB Layer 3 interface?

to provide load balancing
to provide a default VLAN ID
to provide inter-VLAN routing
to provide port security

Answer(s): C

Explanation:

The primary purpose of an IRB (Integrated Routing and Bridging) interface is to enable inter-VLAN routing in a Layer 3 environment. An IRB interface in Junos combines the functionality of both Layer 2 bridging (switching) and Layer 3 routing, allowing devices in different VLANs to communicate with each other.
Step-by-Step Breakdown:
VLANs and Layer 2 Switching:
Devices within the same VLAN can communicate directly through Layer 2 switching. However, communication between devices in different VLANs requires Layer 3 routing.

IRB Interface for Inter-VLAN Routing:
The IRB interface provides a Layer 3 gateway for each VLAN, enabling routing between VLANs. Without an IRB interface, devices in different VLANs would not be able to communicate.
Configuration:
In Juniper devices, the IRB interface is configured by assigning Layer 3 IP addresses to it. These IP addresses serve as the default gateway for devices in different VLANs.
Example configuration:

set interfaces irb unit 0 family inet address 192.168.1.1/24 set vlans vlan-10 l3-interface irb.0
This allows VLAN 10 to use the IRB interface for routing. Juniper

Reference:

IRB Use Case: Inter-VLAN routing is essential in data centers where multiple VLANs are deployed, and Juniper's EX and QFX series switches support IRB configurations for this purpose.

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Juniper JN0-280 Exam (page: 1)
Juniper Data Center, Associate
Updated on: 25-Dec-2025

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Juniper JN0-280 Exam (page: 1) Juniper Data Center, Associate Updated on: 25-Dec-2025

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Juniper JN0-280 Exam (page: 1)
Juniper Data Center, Associate
Updated on: 25-Dec-2025