Important Juniper JN0-281 Exam Questions

Answer: A

Explanation:

Nonstop active routing is the Junos high availability capability that focuses on preserving routing protocol operation and routing information across a Routing Engine switchover. In platforms with redundant Routing Engines, a failure of the primary Routing Engine can otherwise reset routing protocol processes, tear down adjacencies, and trigger reconvergence. NSR mitigates this by synchronizing routing protocol state so that the backup Routing Engine can continue routing protocol operations with minimal disruption. This includes maintaining protocol session continuity and keeping the routing information base stable, which directly protects traffic that depends on those routes.

In data center environments, this is particularly important for routed fabrics where BGP or OSPF underlay reachability supports overlay services and east west application traffic. By keeping routing information consistent during the control-plane transition, NSR reduces route churn and helps avoid transient blackholing or microbursts caused by reconvergence.

GRES is closely related but addresses a different scope. GRES helps the forwarding plane continue forwarding during a Routing Engine switchover by preserving certain system and interface states. However, GRES alone does not guarantee that routing protocol sessions and routing information remain uninterrupted. BFD and LACP are valuable availability tools, but they are not Routing Engine redundancy features and do not preserve routing state during a Routing Engine failover.

Answer: D

Explanation:

In the BGP finite state machine, OpenConfirm indicates that the TCP session is already established and the BGP OPEN message exchange has successfully completed. At this point, both peers have agreed on critical session parameters such as BGP version, autonomous system numbers, hold time, and the BGP identifier. Because the OPEN messages have been processed, BGP transitions from OpenSent to OpenConfirm and then waits for the next control message that validates the session is operational.

Specifically, in OpenConfirm the local BGP process is waiting to receive a KEEPALIVE message from the neighbor, which confirms that the neighbor accepted the OPEN and is ready to bring the session to the Established state. If instead a NOTIFICATION message is received, it indicates an error condition and the session will be torn down. This is why option D is correct.

Option A describes OpenSent, where the router is waiting to receive an OPEN after sending its own OPEN. Option B aligns more closely with Connect, where BGP is still trying to complete the transport connection. Option C relates to Idle, where BGP waits for a start event or configuration to initiate the session. In data center BGP underlays and EVPN control planes, being stuck in OpenConfirm commonly points to policy mismatch, capability negotiation issues, or keepalive handling problems, rather than basic IP reachability.

Answer: D

Explanation:

The exhibit shows BFD liveness detection configured under a BGP group with minimum-interval set to 1000 milliseconds. In Junos, BFD provides rapid failure detection by sending periodic BFD control packets between neighbors. The minimum-interval value is the negotiated minimum transmit and receive interval used for BFD control packets for that session. A neighbor is declared down when the local system fails to receive a certain number of consecutive BFD packets within the expected time window.

That time window is determined by the BFD detection time, which is calculated as the minimum-interval multiplied by the BFD multiplier. The multiplier represents how many BFD control packets can be missed before the session is considered failed. If the multiplier is not explicitly configured, Junos uses the default multiplier value of 3. Therefore, with minimum-interval set to 1000 ms and the default multiplier of 3, the detection time becomes 3000 ms. After approximately 3 seconds without receiving the expected BFD control packets, the BFD session transitions to down and BGP can react by treating the associated peer as unreachable for fast convergence.

This behavior is commonly used in data center underlays and EVPN fabrics to reduce convergence time compared to relying only on BGP hold timers.

Answer: A

Explanation:

In Ethernet switching, the bridge table is the data structure that maps MAC addresses to the switch interfaces where those MAC addresses were learned. Juniper commonly describes this function as the Ethernet switching table and also refers to it as the forwarding table in Layer 2 contexts. The concept is the same: the switch learns source MAC addresses from incoming frames, associates them with an ingress port and VLAN or bridge domain, and then uses that learned information to forward future frames to the correct egress port as known unicast.

Calling it a forwarding table is accurate because its primary operational purpose is deciding how to forward Layer 2 frames efficiently. When a destination MAC is present in the table, the switch performs a unicast forward to the learned port. When a destination MAC is not present, the switch treats it as unknown unicast and floods it within the VLAN or bridge domain, while still learning the source MAC for future use.

The term forwarding information table is more strongly associated with Layer 3 routing, where a FIB represents resolved next hops for IP prefixes in the forwarding plane. That is a different structure than the Layer 2 bridge or MAC table. The other options are not standard Juniper terms for this function.

Verification sources from Juniper documentation

https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic-map/ethernet-switching-components.html

https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/concept/ethernet-switching-table-understanding.html

Answer: B

Explanation:

In Junos BGP configuration, export policy can be applied at multiple levels, including the BGP group level and the individual neighbor level. When an export policy is configured directly under a specific neighbor, that policy is explicitly associated with advertisements sent to that neighbor and is therefore the policy that applies to that neighbor. In the exhibit, neighbor 172.16.1.101 has an export statement configured within the neighbor stanza, and that statement references the advertise-ospf policy. This is the most specific policy attachment in the configuration because it is tied to a single peer rather than to the entire group or the whole BGP process.

Group-level export policies, such as advertise-aggregate configured under the group, apply broadly to all neighbors in that group unless a neighbor has additional neighbor-specific policy. A BGP-level export policy configured outside the group applies as a more general export policy scope. However, the question asks which export policy applies to the specific neighbor, and the correct selection is the neighbor-specific export policy that is explicitly configured for that peer.

Operationally, this allows data center engineers to advertise different route sets to different peers, for example exporting OSPF-derived infrastructure routes to one neighbor while exporting aggregates or static routes to another, all while keeping a consistent group template for shared settings such as peer AS and session type.