JN0-281 Exam Results

On Junos devices used in data centers, an aggregated Ethernet bundle can run either static bundling or dynamic bundling using LACP. When LACP is used, Junos supports two negotiation modes: active and passive. These modes control whether the device initiates LACP negotiation by transmitting LACP Data Units or whether it waits to respond to LACP Data Units sent by its peer. In active mode, the system periodically sends LACP control frames to begin and maintain the negotiation. In passive mode, the system does not initiate negotiation but will respond if it receives LACP control frames from the neighbor.

From an operational perspective, active is typically recommended on at least one side of the link so the bundle reliably forms even if the peer is configured to be passive. If both ends are passive, each side waits for the other to start, and the aggregated link might not come up as expected. This is a common cause of down or partially formed bundles in leaf spine uplinks and server dual-homing scenarios.

Options aggressive and mixed are not Junos LACP modes for aggregated Ethernet. In Junos, you configure LACP under the aggregated-ether-options hierarchy and select active or passive behavior, along with optional timing such as periodic fast for quicker detection.

Bidirectional Forwarding Detection is a lightweight, fast failure-detection mechanism used to quickly determine whether a forwarding path between two systems is operational. In Juniper data center networks, BFD is commonly paired with routing protocols such as BGP and OSPF to accelerate convergence. Instead of waiting for a routing protocol hold timer or dead interval to expire, BFD continuously exchanges small control packets between neighbors at a configured interval. If the local device stops receiving these control packets for a negotiated detection time, it declares the BFD session down.

This down event can then be used to immediately signal the routing protocol that the neighbor is no longer reachable, causing faster withdrawal of routes or faster reroute to alternate paths. This is critical in leaf-spine fabrics where rapid failover is expected to maintain application availability and to keep ECMP path sets current. BFD is designed to detect failures in the forwarding plane, including link failures, interface failures, or other failures that prevent packets from being successfully exchanged between the two endpoints. It is not intended to detect routing loops, and it does not specifically track route flaps as a function; flapping is a symptom that may occur when failures happen repeatedly.

Destination host unreachable messages are part of ICMP processing and are unrelated to BFD’s purpose. In short, BFD’s value is fast, protocol-independent failure detection for forwarding adjacency health.

Generated routes in Junos are used to conditionally create a route in the routing table when specific criteria are satisfied. They are policy-driven and allow operators to inject a prefix only when the device has the necessary supporting reachability or other configured conditions. This is useful in data center environments to ensure that certain aggregate or service prefixes are advertised only when the infrastructure can truly forward traffic toward the intended destinations. For example, a generated route can be used to advertise a summary prefix into BGP only if one or more contributing routes exist, preventing blackholing that could occur if a summary is advertised while downstream reachability is missing.

Generated routes do not create a separate routing table; routing tables are created by routing instances and related configuration constructs. They also are not intended simply to increase the number of advertisements. Their value is correctness and control, not volume. Finally, expanding a single advertisement into multiple routes is not the purpose of generated routes; that behavior is more aligned with route policies that manipulate announcements, prefix lists, or mechanisms that originate multiple prefixes by configuration.

In short, generated routes provide conditional route origination based on defined match conditions, enabling safer summarization and controlled advertisement patterns that are common in scalable data center routing designs.

On Junos switching platforms commonly used in data centers, a VLAN is a Layer 2 construct that defines a broadcast domain. To make a VLAN usable, you define the VLAN using a name and typically a VLAN ID, then associate Layer 2 interfaces with it so traffic entering those interfaces is placed into that VLAN. Without membership on interfaces, the VLAN exists in configuration but does not carry user traffic, because no ports participate in that broadcast domain.

Trunk mode interfaces are specifically designed to carry traffic for multiple VLANs over a single physical link, such as between switches, to servers using tagging, or to other network devices that understand VLAN tags. In Junos, trunking is implemented by allowing a list of VLAN IDs on the trunk so the interface accepts and forwards frames for those VLANs. This makes statement C correct.

An IRB interface is not mandatory for every VLAN. IRB is used when you want Layer 3 routing for a VLAN, typically to provide a default gateway and enable inter VLAN routing. Pure Layer 2 VLANs do not require IRB, which makes statement A incorrect.

Access mode interfaces are intended to connect to a single endpoint and carry traffic for a single VLAN, so assigning multiple VLANs to an access interface is not correct in standard access mode behavior, making statement D incorrect.