Juniper JN0-281 Exam Practice Test Instant Access

Question 1

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

AThe order of the AS path is not significant.

BThe local AS number is added to the end of the AS path.

CThe order of the AS path is only significant in IBGP.

DThe local AS number is added to the beginning of the AS path.

Answer : D

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.

Juniper 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.

Question 2

What are two reasons why you would deploy an IP fabric instead of a traditional Layer 2 network in a data center? (Choose two.)

ALayer 2 networks only support a single broadcast domain.

BIP fabrics are better suited to smaller networks where scale is less important.

CLayer 3 networks support load balancing.

DLayer 2 networks are susceptible to loops.

Answer : C, D

IP fabrics are Layer 3-centric network designs often used in data centers due to their scalability, efficient routing, and loop-free architecture.

Step-by-Step Breakdown:

Layer 3 Load Balancing:

IP fabrics use Equal-Cost Multipath (ECMP) to distribute traffic across multiple paths, providing effective load balancing and improving bandwidth utilization. This capability is absent in traditional Layer 2 networks, which do not support ECMP for routing decisions.

Layer 2 Loops:

Layer 2 networks are prone to loops because of the lack of TTL (Time-to-Live) mechanisms. Spanning Tree Protocol (STP) is required to prevent loops, but it can introduce inefficiencies by blocking links. In contrast, IP fabrics based on Layer 3 protocols are loop-free and do not need STP.

Juniper Reference:

IP Fabric: Juniper's IP fabric solutions offer efficient Layer 3 routing with built-in load balancing and loop prevention, making them ideal for modern data center architectures.

Question 3

When using spine and leaf fabric architectures, what is the role of each device? (Choose two.)

ASpine nodes are used for host connectivity.

BSpine nodes are used for transit to other leaf nodes.

CLeaf nodes are used for traffic to other leafs.

DLeaf nodes are used for host connectivity.

Answer : B, D

In a spine-leaf fabric architecture, which is commonly used in data center designs, each device has a distinct role to ensure efficient and scalable network traffic flow.

Step-by-Step Breakdown:

Spine Nodes:

The spine nodes form the backbone of the fabric and are responsible for transit traffic between leaf nodes. They connect to every leaf switch and provide multiple paths for traffic between leaf nodes, ensuring redundancy and load balancing.

Leaf Nodes:

The leaf nodes are used for host connectivity. These switches connect to servers, storage, or edge routers. They also connect to the spine switches to reach other leaf switches.

Juniper Reference:

Spine-Leaf Architecture: In Juniper's IP fabric designs, spine switches handle inter-leaf communication, while leaf switches manage host and endpoint connectivity.

Question 4

Which two statements are correct about EVPN-VXLAN overlay networking? (Choose two.)

AIt is the only option to provide reachability between servers that reside in the same network segment in a data center.

BBGP provides the control plane within the overlay network.

CAn encapsulation of the original packet is required to transport the packet across the network.

DOSPF provides the control plane within the overlay network.

Answer : B, C

EVPN-VXLAN is an overlay technology used in data center networks to extend Layer 2 services over a Layer 3 network.

Step-by-Step Breakdown:

BGP Control Plane:

BGP (Border Gateway Protocol) is used as the control plane for EVPN-VXLAN. BGP advertises MAC addresses and IP address reachability information across the VXLAN network, enabling efficient multi-tenant Layer 2 connectivity over a Layer 3 infrastructure.

Encapsulation:

VXLAN (Virtual Extensible LAN) encapsulates Layer 2 frames into Layer 3 packets. This encapsulation allows Layer 2 traffic to be transported across a Layer 3 network, effectively creating a tunnel for Ethernet frames.

Juniper Reference:

EVPN-VXLAN Configuration: Juniper supports EVPN-VXLAN with BGP as the control plane, allowing scalable Layer 2 connectivity over a routed infrastructure in modern data centers.

Question 5

Exhibit:

How many stages are shown in the exhibit?

Answer : D

The exhibit shows a Folded IP Clos Architecture, which is also referred to as a 3-stage Clos network design. This architecture typically consists of two layers of switches:

Spine Layer: The top row of switches.

Leaf Layer: The bottom row of switches.

Step-by-Step Breakdown:

Clos Architecture:

A 3-stage Clos network has two types of devices: spine and leaf. In this design, each leaf switch connects to every spine switch, providing a high level of redundancy and load balancing.

Stage Explanation:

Stage 1: The first set of leaf switches.

Stage 2: The spine switches.

Stage 3: The second set of leaf switches.

The Folded Clos architecture shown here effectively 'folds' the 3-stage design by combining the ingress and egress leaf layers into one, reducing it to two visible layers, but still maintaining the overall 3-stage architecture.

Juniper Reference:

IP Clos Architecture: The 3-stage Clos design is commonly used in modern data centers for high availability, redundancy, and scalability.

Question 6

Which statement is correct about aggregate routes?

AThe default next hop is discard.

BThe default next hop is readvertise.

CThe default next hop is resolve.

DThe default next hop is reject.

Answer : D

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.

Juniper 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.

Question 7

Exhibit:

Referring to the exhibit, which statement is correct?

AThe configuration will commit successfully and BGP group 1 will operate as IBGP.

BThe configuration will commit successfully and BGP group 1 will operate as EBGP.

CBGP group 1 requires a type external parameter.

DBGP group 1 requires a type internal parameter.

Answer : B

In the exhibit, BGP is configured with local AS 65101 and a neighbor at 172.16.1.1 in peer AS 65201. This setup involves two different Autonomous Systems (AS), indicating an External BGP (EBGP) configuration.

Step-by-Step Breakdown:

EBGP vs. IBGP:

EBGP is used between routers in different ASes. In this case, the local AS is 65101 and the peer AS is 65201, meaning the BGP session is EBGP.

IBGP is used between routers within the same AS, which is not applicable here as the AS numbers are different.

BGP Group Configuration:

The configuration does not require a type external parameter because Junos OS automatically recognizes the session as EBGP when the local and peer AS numbers are different.

The BGP session will operate as EBGP, and the configuration will commit successfully.

Juniper Reference:

BGP Configuration: In Juniper, EBGP is automatically recognized when the local and peer AS numbers differ, without needing to specify type external.

Juniper Data Center, Associate JN0-281 Exam Practice Test