Free JNCIA-DC certification exam Practice Questions

Sample Practice Questions

Try these 10 sample questions from the JNCIA-DC certification exam practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1Which sequence names the tiers in a traditional multitier data center network, from server-facing connectivity toward the backbone?

   1. A. Leaf, spine, super spine
   2. B. Access, aggregation, core
   3. C. Core, access, aggregation
   4. D. Aggregation, core, access

   Answer: B

   Explanation: Juniper describes "traditional multitier access-aggregation core networks". Access is the server-facing tier, aggregation combines access connectivity, and core provides backbone connectivity.

   Reference: This Week: Data Center Deployment with EVPN/VXLAN — Chapter 1, Types of Network Underlay, p. 9

2. 2A switch receives a frame from a previously unseen host on ge-0/0/5. Which information does normal dynamic MAC learning associate with ge-0/0/5?

   1. A. The frame's destination IP address
   2. B. The frame's destination MAC address
   3. C. The frame's source MAC address
   4. D. The frame's source TCP port

   Answer: C

   Explanation: Juniper states that the switch "learns the embedded MAC addresses of the sending nodes". It associates the sender address with the receiving interface, rather than learning the destination from this frame.

   Reference: Bridging and VLANs — How Bridging of VLAN Traffic Works, Learning

3. 3For a basic manually configured static route with an IP next hop, what condition is required for activation and installation in the forwarding table?

   1. A. The destination must first be advertised by BGP.
   2. B. The route must have at least one more-specific contributor.
   3. C. The configured next-hop address must be reachable.
   4. D. The route must be attached to an OSPF export policy.

   Answer: C

   Explanation: Juniper states that the static route is installed "when the next-hop address is reachable". Static routes do not require BGP, OSPF redistribution, or aggregate-style contributing routes.

   Reference: Protocol-Independent Routing Properties User Guide — Understand Basic Static Routing, p. 22

4. 4After OSPF has converged, which relationship should hold among the topology databases of routers within the same area?

   1. A. They contain identical area topology information.
   2. B. Each contains only links directly attached to its router.
   3. C. Only the DR retains a complete copy of the area topology.
   4. D. They contain identical copies of every other area's detailed topology.

   Answer: A

   Explanation: Juniper states, "Within each area, OSPF routers have identical topological databases." Each router calculates routes from the shared area topology, with itself as the root of its shortest-path tree.

   Reference: OSPF User Guide — OSPF Overview, p. 3

5. 5What does ordinary Ethernet link aggregation present to the MAC client?

   1. A. A separate routing instance for each member interface
   2. B. One spanning-tree root for each member interface
   3. C. A single logical link formed from member links
   4. D. A separate broadcast domain for each member link

   Answer: C

   Explanation: Juniper describes grouping Ethernet interfaces "to form a single link layer interface". The LAG is treated as a logical link while traffic can use its member links.

   Reference: Aggregated Ethernet Interfaces Overview — Overview, opening paragraph

6. 6How are leaf devices connected in a typical three-stage spine-and-leaf IP fabric?

   1. A. Each leaf connects to one spine, with spines connected in a ring.
   2. B. Each leaf connects to adjacent leaves, with one leaf connected upstream.
   3. C. Each leaf connects to each spine in the fabric.
   4. D. Each leaf connects to every other leaf instead of to spines.

   Answer: C

   Explanation: The reference architecture states "each leaf device is connected to each spine device". This produces the spine-and-leaf connectivity of the three-stage fabric.

   Reference: IP Fabric EVPN-VXLAN Reference Architecture — IP Fabric Underlay Network, p. 3

7. 7A unicast frame enters ge-0/0/1 in VLAN 20. Its destination MAC has a valid entry on ge-0/0/8 in VLAN 20. With no filtering restrictions, how does the switch forward the frame?

   1. A. Through ge-0/0/8 toward the known destination
   2. B. Through every forwarding port in VLAN 20
   3. C. Through every trunk regardless of VLAN membership
   4. D. Through ge-0/0/1 back toward the sender

   Answer: A

   Explanation: Juniper explains, "If the location of a node is known, the frame is sent directly to that node." The destination lookup identifies ge-0/0/8, so flooding is unnecessary.

   Reference: Bridging and VLANs — How Bridging of VLAN Traffic Works, forwarding

8. 8What is the principal routing-information benefit of advertising an aggregate while suppressing its contributing routes?

   1. A. Receiving routers can learn one summary instead of many more-specific routes.
   2. B. The aggregating router deletes every contributing route from its own table.
   3. C. The receiving routers install every contributor without receiving advertisements.
   4. D. The aggregating router can forward without retaining any next-hop information.

   Answer: A

   Explanation: Juniper describes "consolidating selected multiple routes into a single route advertisement". The benefit is seen by receivers when only the aggregate is exported; the local contributing routes remain.

   Reference: Protocol-Independent Routing Properties User Guide — Understanding Route Aggregation, p. 105

9. 9Which OSPF packet type establishes and maintains neighbor relationships?

   1. A. Database Description
   2. B. Link-State Request
   3. C. Link-State Update
   4. D. Hello

   Answer: D

   Explanation: Juniper states that routers send "hello packets" to "establish and maintain neighbor relationships". The other packet types support database synchronization or LSA transfer.

   Reference: OSPF User Guide — OSPF Packets Overview, Hello Packets, p. 8

10. 10Which statement correctly describes the relationship between an aggregated Ethernet interface and LACP in Junos?

    1. A. An aggregated Ethernet interface can be configured with or without LACP.
    2. B. An aggregated Ethernet interface requires LACP whenever it has more than one member.
    3. C. LACP can be used only when the Ethernet interfaces remain separate logical links.
    4. D. LACP replaces the need to assign physical members to an aggregated interface.

    Answer: A

    Explanation: Juniper states, "You can configure aggregated Ethernet with or without LACP enabled." LACP adds negotiation and link-state exchange; aggregation is also possible without it.

    Reference: Layer 2 Networking — Configuring an Aggregated Ethernet Interface and Configuring LACP on That Interface