Juniper JN0-280 Data Center, Associate JNCIA-DC Exam Practice Test

Answer : B, D

In Layer 2 switching, switches learn MAC addresses based on the source MAC address of incoming frames and forward frames based on the destination MAC address.

Step-by-Step Breakdown:

MAC Learning:

When a switch receives a frame, it records the source MAC address and the port on which it arrived. This allows the switch to know where to send traffic destined for that MAC address.

Forwarding Based on Destination:

The switch then looks at the destination MAC address and forwards the frame out of the port associated with that MAC address. If the MAC is unknown, the switch floods the frame to all ports.

Juniper Reference:

Layer 2 Switching: Juniper switches use source MAC addresses to build MAC tables and forward traffic based on the destination MAC address.

Answer : C

Graceful Restart (GR) is a feature that allows a router to maintain forwarding even when the routing process (e.g., the rpd process in Junos) is restarting, minimizing disruption to the network.

Step-by-Step Breakdown:

Graceful Restart Function:

During a GR event, the forwarding plane continues to forward packets based on existing routes, while the control plane (rpd process) is restarting. This prevents traffic loss and maintains routing stability.

Minimizing Disruptions:

GR is particularly useful in ensuring continuous packet forwarding during software upgrades or routing protocol process restarts.

Juniper Reference:

Graceful Restart in Junos: GR ensures high availability by maintaining forwarding continuity during control plane restarts, enhancing network reliability.

Answer : C

Per-flow load balancing ensures that packets within the same flow are always forwarded over the same path, ensuring that packet order is preserved.

Step-by-Step Breakdown:

Flow Definition:

A flow is typically defined by a combination of packet attributes like source/destination IP, source/destination port, and protocol type. Packets that belong to the same flow are routed over the same path to avoid reordering.

Per-Flow Behavior:

In per-flow load balancing, the hashing algorithm ensures that all packets in a particular flow use the same egress port, maintaining order across the network.

Juniper Reference:

Load Balancing in Juniper: This method ensures that flows are balanced across multiple paths while preventing packet reordering within a single flow.

Answer : A

Bidirectional Forwarding Detection (BFD) is a network protocol used to detect failures in the network path between two devices quickly.

Step-by-Step Breakdown:

Path Failure Detection:

BFD provides a low-overhead mechanism for detecting failures in forwarding paths across Layer 3 networks. It is much faster than traditional routing protocol timers and can detect failures within milliseconds.

BFD in Routing:

BFD can be integrated with routing protocols like OSPF, BGP, or IS-IS to trigger a faster convergence when a network path goes down.

Juniper Reference:

BFD Configuration: Juniper devices use BFD to monitor network paths and ensure fast failure detection, enhancing network resilience.

Answer : A, B

An IP fabric is a network architecture commonly used in data centers to provide scalable, high-throughput connectivity using a spine-leaf topology.

Step-by-Step Breakdown:

Layer 3 Routing Protocol:

An IP fabric relies on a Layer 3 routing protocol, typically BGP or OSPF, to provide routing between the leaf and spine switches. This ensures efficient traffic forwarding across the network.

Single Connection Between Spine and Leaf:

In an IP fabric, each leaf switch connects to every spine switch with a single connection. This ensures that traffic between any two leaf switches can travel through the spine layer in just two hops.

Juniper Reference:

Spine-Leaf Design: Juniper's IP fabric implementations are designed for scalability and low-latency routing, often using protocols like BGP for Layer 3 control.

Answer : B, C

When configuring an aggregate route, you have options for how to handle traffic that matches the route but does not match any more specific route in the routing table. Two actions can be taken: discard and reject.

Step-by-Step Breakdown:

Discard:

The discard option will silently drop packets that match the aggregate route. No notification is sent to the sender, and the packet is simply dropped.

Reject:

The reject option will drop the packet and also send an ICMP Destination Unreachable message back to the sender. This informs the sender that the packet could not be delivered because there is no specific route available.

Juniper Reference:

Aggregate Routes: The reject and discard next-hop options provide different levels of feedback when packets cannot be routed, and they can be used to control how unreachable destinations are handled.

Answer : B

The source MAC address in the Ethernet header is used to populate the bridging table (also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with the ingress port in its MAC address table.

Step-by-Step Breakdown:

Learning Process:

When an Ethernet frame arrives on a switch port, the switch looks at the source MAC address and adds this MAC address to the MAC table along with the port it was received on. This process is called MAC learning.

Purpose:

The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding.

Juniper Reference:

Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.