Juniper JN0-280 Exam Questions in PDF and Online

QUESTION: 6

Which two statements describe an IP fabric? (Choose two.)

An IP fabric allows devices to always be one hop away.
An IP fabric depends on Layer 2 switching.
An IP fabric uses spine and leaf devices.
An IP fabric provides traffic load sharing.

Answer(s): C,D

Explanation:

An IP fabric is a network topology designed to provide a scalable, low-latency architecture that is typically implemented in modern data centers. It uses spine and leaf switches and enables efficient traffic load sharing across the network.
Step-by-Step Breakdown:
Spine-Leaf Architecture:
Leaf Devices: These switches connect to servers and edge devices within the data center. Each leaf switch connects to every spine switch.
Spine Devices: These high-performance switches interconnect all the leaf switches. There are no direct connections between leaf switches or spine switches. This architecture ensures that any two endpoints within the fabric are only one hop away from each other, minimizing latency.
Traffic Load Sharing:
An IP fabric leverages Equal-Cost Multipath (ECMP) to distribute traffic evenly across all available paths between leaf and spine switches, providing effective load balancing. This ensures that no single link becomes a bottleneck and that traffic is distributed efficiently across the network.

Reference:

Juniper provides QFX Series switches optimized for IP fabric topologies, allowing for scalable deployments in modern data centers.
EVPN-VXLAN: Often used in IP fabrics to extend Layer 2 services across the fabric with Layer 3 underlay, enabling both efficient routing and bridging.

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QUESTION: 7

Referring to the exhibit, why are the BGP routes hidden?

Load balancing is not enabled.
There are too many hops to the destination.
The BGP next hop is unreachable.
Other routes are selected because of better metrics.

Answer(s): C

Explanation:

In the exhibit, the BGP routes are marked as hidden. This typically happens when the routes are not considered valid for use, but they remain in the routing table for reference. One common reason for

BGP routes being hidden is that the next hop for these routes is unreachable.
Step-by-Step Breakdown:
BGP Next Hop:
In BGP, when a route is received from a neighbor, the next hop is the IP address that must be reachable for the route to be used. If the next hop is unreachable (i.e., the router cannot find a path to the next-hop IP), the route is marked as hidden.
Analyzing the Exhibit:
The exhibit shows that the BGP next hop for all hidden routes is 10.4.4.4. If this IP is unreachable, the BGP routes from that neighbor will not be considered valid, even though they appear in the routing table.
Verification:
Use the command show route 10.4.4.4 to check if the next-hop IP is reachable.

If the next-hop is not reachable, the BGP routes will be hidden. Resolving the next-hop reachability issue (e.g., fixing an IGP route or an interface) will allow the BGP routes to become active.

Reference:

Junos Command: show route hidden displays routes that are not considered for forwarding. Troubleshooting: Check the next hop reachability for hidden BGP routes using show route <next- hop>.

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QUESTION: 8

Which statement is correct about the BGP AS path when advertising routes?

The order of the AS path is not significant.
The local AS number is added to the end of the AS path.
The order of the AS path is only significant in IBGP.
The local AS number is added to the beginning of the AS path.

Answer(s): D

Explanation:

The BGP AS (Autonomous System) path attribute is crucial in path selection and loop prevention. Each BGP router appends its local AS number to the beginning of the AS path when it advertises a route to an external BGP (eBGP) peer.
Step-by-Step Breakdown:
AS Path Attribute:
The AS path is a sequence of AS numbers that a route has traversed to reach a destination. Each AS adds its number to the front of the path, allowing BGP to track the route's history.
Why the Local AS is Added at the Beginning:
When advertising a route to an eBGP neighbor, a BGP router adds its own AS number to the beginning of the AS path. This ensures that the AS path reflects the route's journey accurately from the origin to the destination, and prevents loops in BGP. If the route returns to the same AS, the router will detect its AS number in the path and reject the route, preventing routing loops.
Order of the AS Path:
The order is significant because BGP uses it to select the best path. A shorter AS path is preferred, as it indicates fewer hops between the source and destination.

Reference:

AS Path Attribute: Junos devices append the local AS at the start of the AS path before advertising the route to an external peer.

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QUESTION: 9

Which statement is correct about a three-stage IP fabric underlay?

Every ingress interface into the fabric is only two hops away from the egress interface.
Every spine device can communicate directly with other spine devices.
Every leaf device can communicate directly with other leaf devices.
Every server that connects to a three-stage IP fabric must be multihomed.

Answer(s): A

Explanation:

In a three-stage IP fabric (also known as a Clos fabric), traffic between any two points (ingress to egress) in the fabric is only two hops away.
Step-by-Step Breakdown:
Three-Stage IP Fabric:
Leaf Layer: Leaf switches connect directly to servers and edge devices. Spine Layer: Spine switches provide connectivity between leaf switches but do not connect to each other directly.
Two-Hop Communication:
In this architecture, every leaf switch is connected to every spine switch. Therefore, when a packet enters the fabric via an ingress leaf switch, it is forwarded to a spine switch, which then directs the packet to the correct egress leaf switch. This path always involves exactly two hops:
Ingress leaf Spine Egress leaf.
Benefits:
This consistent two-hop path ensures predictable latency and makes the network highly scalable while maintaining low complexity.

Reference:

IP Fabric Architecture: This two-hop property of Clos fabrics is a hallmark of spine-leaf designs, as supported by Juniper's QFX and EX switches in data centers.

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QUESTION: 10

A routing policy has been created to advertise OSPF routes in BGP.
Which statement is correct in this scenario?

Apply the policy as an export policy within BGP.
Apply the policy as an export policy within OSPF.
Apply the policy as an import policy within BGP.
Apply the policy as an import policy within OSPF.

Answer(s): A

Explanation:

When advertising OSPF routes into BGP, the appropriate routing policy should be applied as an export policy in BGP.
Step-by-Step Breakdown:
OSPF to BGP Route Advertisement:
Routes learned via OSPF (a dynamic IGP) need to be exported into BGP to be advertised to external BGP peers. In Junos OS, this is done using export policies.
Export Policies in BGP:
An export policy controls which routes are advertised out of a BGP session. In this scenario, the routing policy must be applied to BGP as an export policy to export the OSPF-learned routes to external BGP peers.
Policy Configuration:

Example configuration:

set policy-options policy-statement EXPORT_OSPF term 1 from protocol ospf set policy-options policy-statement EXPORT_OSPF term 1 then accept set protocols bgp group <group-name> export EXPORT_OSPF This policy ensures that only OSPF routes are exported into BGP.

Reference:

Routing Policy: Export policies are used in BGP to control route advertisements to peers, including those learned via OSPF.

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Juniper Data Center, Associate JN0-280 Exam Questions in PDF

Free Juniper JN0-280 Dumps Questions (page: 2)

QUESTION: 6

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QUESTION: 7

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QUESTION: 8

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QUESTION: 9

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QUESTION: 10

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