Latest Juniper JN0-281 Practice Questions By Harrell

Nonstop bridging is a high availability capability focused on maintaining Layer 2 switching continuity during a Routing Engine switchover on platforms that support redundant control planes. The intent is to keep Layer 2 forwarding operational and minimize disruption to bridged traffic when the system transitions from a primary to a backup Routing Engine. Achieving this requires Graceful Routing Engine switchover, because GRES is the mechanism that enables a control plane switchover while keeping forwarding and interface state stable. With GRES in place, the forwarding plane can continue switching frames while the backup Routing Engine assumes control, reducing or eliminating traffic loss for Layer 2 domains.

Nonstop bridging is not the feature that preserves Layer 3 protocol sessions and routing information end-to-end. That function is associated with nonstop routing capabilities, which focus on maintaining routing protocol state across Routing Engine events. Therefore, stating that nonstop bridging preserves Layer 3 information and protocol sessions is incorrect. Likewise, nonstop active routing is not a requirement for nonstop bridging; it is a separate feature aimed at routing stability. The flow-control setting under gigether-options is unrelated to Routing Engine redundancy and does not determine whether nonstop bridging operates.

In data center access and aggregation environments where VLANs must remain stable for servers and appliances, nonstop bridging paired with GRES helps protect Layer 2 service continuity during control plane events.

A data center underlay IP fabric is a routed leaf-spine network designed to provide scalable Layer 3 connectivity between all fabric nodes. A key property of these fabrics is that there are multiple equal-cost paths between any two endpoints, typically across multiple spine devices. Equal-Cost Multi-Path load balancing is used to distribute traffic across those parallel paths. The routing table installs multiple next hops for the same destination prefix, and the forwarding plane selects an egress link per flow using a hash, which keeps packets in-order within a flow while using the fabric's aggregate bandwidth. This makes statement B correct.

Because the underlay is routed, loop avoidance is handled by the routing protocol and the fundamental properties of IP forwarding, not by spanning tree. Routing protocols compute a loop-free forwarding topology and use mechanisms like shortest-path calculation and next-hop selection so that even when multiple paths exist, traffic is forwarded along valid loop-free routes. This makes statement C correct. Statement D is incorrect because spanning tree is a Layer 2 loop prevention mechanism and is not required or desired in a routed underlay fabric. Statement A is also incorrect because traffic distribution depends on ECMP and forwarding behavior, not on all devices being the same hardware model. Mixed platforms can interoperate as long as the design accounts for capacity, features, and consistent routing behavior.