[2025年05月17日] 無料JNCIA-DC JN0-281公式認定ガイドPDFダウンロード
Juniper JN0-281公式認定ガイドPDF
質問 # 71
You are configuring OSPF in your network as shown in the exhibit. R1 has been configured with interface metrics. All other links in the network are using the default interface metric.
In this scenario, which OSPF interface on R1 will be preferred when routing traffic between R1 and R5?
- A. ge-0/0/0
- B. ge-0/0/3
- C. ge-0/0/2
- D. ge-0/0/1
正解：D
質問 # 72
Which statement is correct about per-flow load balancing?
- A. The packets are guaranteed to arrive at their destination in the same order in which they were sent.
- B. The packets are guaranteed to arrive at their destination in a different order in which they were sent.
- C. Packets associated with the same flow are sent through different egress ports.
- D. Packets associated with the same flow are sent through the same egress port.
正解：D
解説：
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.
質問 # 73
In OSPF, which command is commonly used to monitor neighbor relationships?
- A. show ip route ospf
- B. show ospf database
- C. show ip ospf neighbors
- D. show ospf interfaces
正解：C
質問 # 74
Which signaling protocol is used for EVPN?
- A. OSPF
- B. BGP
- C. IS-IS
- D. PIM
正解：B
解説：
EVPN (Ethernet Virtual Private Network) is a standard protocol used for building Layer 2 and Layer 3 VPNs over an IP or MPLS network. The signaling protocol used for EVPN is BGP (Border Gateway Protocol).
Step-by-Step Breakdown:
BGP as the EVPN Signaling Protocol:
EVPN uses BGP to exchange MAC address reachability information between routers (PE devices). This enables devices to learn which MAC addresses are reachable through which PE devices, facilitating Layer 2 forwarding across an IP or MPLS core.
BGP Extensions for EVPN:
BGP is extended with new address families (e.g., EVPN NLRI) to carry both MAC and IP address information, allowing for scalable and efficient multi-tenant network solutions.
Juniper Reference:
Junos EVPN Configuration: Juniper uses BGP as the control plane for EVPN to exchange MAC and IP route information between different data center devices.
質問 # 75
Which two statements describe an IP fabric? (Choose two.)
- A. An IP fabric uses spine and leaf devices.
- B. An IP fabric provides traffic load sharing.
- C. An IP fabric allows devices to always be one hop away.
- D. An IP fabric depends on Layer 2 switching.
正解：A、B
解説：
An IP fabric is a network topology designed to provide a scalable, low-latency architecture that is typically implemented in modern data centers. It uses spine and leaf switches and enables efficient traffic load sharing across the network.
Step-by-Step Breakdown:
Spine-Leaf Architecture:
Leaf Devices: These switches connect to servers and edge devices within the data center. Each leaf switch connects to every spine switch.
Spine Devices: These high-performance switches interconnect all the leaf switches. There are no direct connections between leaf switches or spine switches. This architecture ensures that any two endpoints within the fabric are only one hop away from each other, minimizing latency.
Traffic Load Sharing:
An IP fabric leverages Equal-Cost Multipath (ECMP) to distribute traffic evenly across all available paths between leaf and spine switches, providing effective load balancing. This ensures that no single link becomes a bottleneck and that traffic is distributed efficiently across the network.
Juniper Reference:
Juniper provides QFX Series switches optimized for IP fabric topologies, allowing for scalable deployments in modern data centers.
EVPN-VXLAN: Often used in IP fabrics to extend Layer 2 services across the fabric with Layer 3 underlay, enabling both efficient routing and bridging.
質問 # 76
Which two statements are correct about aggregate routes and generated routes? (Choose two.)
- A. An aggregate route has a forwarding next hop.
- B. A generated route has a forwarding next hop.
- C. An aggregate route does not have a forwarding next hop.
- D. A generated route does not have a forwarding next hop.
正解：B、C
解説：
Aggregate routes and generated routes are used to create summarized routes in Junos, but they behave differently in terms of forwarding.
Step-by-Step Breakdown:
Aggregate Routes:
An aggregate route summarizes a set of more specific routes, but it does not have a direct forwarding next hop. Instead, it points to the more specific routes for actual packet forwarding.
Generated Routes:
A generated route also summarizes specific routes, but it has a forwarding next hop that is determined based on the availability of contributing routes. The generated route can be used to directly forward traffic.
Juniper
Reference: Aggregate and Generated Routes: In Junos, aggregate routes rely on more specific routes for forwarding, while generated routes can forward traffic directly based on their next-hop information.
質問 # 77
Referring to the exhibit, which statement is true?
- A. BFD only records a syslog message if three BFD packets are missed.
- B. BFD will bring down the BGP session if no BFD packets are received for 2700 milliseconds.
- C. BFD packets are being sent every second.
- D. BFD will bring down the BGP session if no BFD packets are received for 2700 seconds.
正解：B
質問 # 78
In a traditional multi-tier architecture, which layer is responsible for aggregating access layers and providing connectivity to the core layer?
- A. Edge Layer
- B. Access Layer
- C. Distribution Layer
- D. Core Layer
正解：C
質問 # 79
What is the primary purpose of using static routes in a network?
- A. To automatically adjust routes based on network traffic
- B. To aggregate multiple routes into one
- C. To provide a manually configured routing entry
- D. To generate routing entries dynamically
正解：C
質問 # 80
Exhibit:
R2 received an OSPF update from R1, and it received the same update from R3.
Referring to the exhibit, what will R2 do?
- A. R2 does nothing with R3's update.
- B. R2 ignores the update from R1.
- C. R2 ignores the update from R3.
- D. R2 acknowledges R3 and discards it.
正解：C
解説：
In the exhibit, R2 receives the same OSPF update from both R1 and R3. OSPF has mechanisms to prevent unnecessary processing of duplicate LSAs (Link-State Advertisements).
Step-by-Step Breakdown:
OSPF LSA Processing:
OSPF uses LSAs to exchange link-state information between routers. When a router receives an LSA, it checks if it already has a copy of the LSA in its Link-State Database (LSDB).
Duplicate LSAs:
If R2 has already received and processed the update from R1, it will ignore the update from R3 because it already has the same LSA in its database. OSPF uses the concept of flooding, but it does not reprocess LSAs that it already knows about.
R2 Behavior:
R2 will keep the update from R1 (the first one it received) and will ignore the same LSA from R3, as it is already in the LSDB.
Juniper Reference:
OSPF LSA Processing: Junos adheres to OSPF standards, ensuring that duplicate LSAs are not processed multiple times to avoid unnecessary recalculations.
質問 # 81
Which two statements are true about how switches handle Layer 2 traffic? (Choose two.)
- A. Traffic is forwarded based on the source MAC address.
- B. The MAC address is learned based on the destination MAC address.
- C. The MAC address is learned based on the source MAC address.
- D. Traffic is forwarded based on the destination MAC address.
正解：C、D
解説：
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.
質問 # 82
In a Spine/Leaf IP-Fabric architecture, what is the primary role of the leaf switches?
- A. To perform deep packet inspection.
- B. To interconnect different data centers.
- C. To provide direct connectivity to servers.
- D. To manage the overall data center network.
正解：C
質問 # 83
Which three technologies improve high availability and convergence in a data center network? (Choose three.)
- A. link aggregation group (LAG)
- B. Bidirectional Forwarding Detection (BFD)
- C. Failover Group (FG)
- D. graceful restart (GR)
- E. link loss adjacency
正解：A、B、D
解説：
High availability and fast convergence are critical in data center networks to minimize downtime and maintain optimal performance. The following technologies contribute to achieving these goals:
Graceful Restart (GR):
GR allows routers to maintain forwarding state during control plane restarts, ensuring continuous packet forwarding while minimizing network disruptions.
Bidirectional Forwarding Detection (BFD):
BFD provides fast detection of path failures, allowing routing protocols to converge quickly by detecting link failures much faster than traditional timers.
Link Aggregation Group (LAG):
LAG increases both redundancy and bandwidth by combining multiple physical links into one logical link, providing load balancing and fault tolerance.
Juniper Reference:
High Availability Techniques: These technologies are fundamental in ensuring rapid recovery and failover within Juniper-based data center environments.
質問 # 84
What is the default route preference of a static route in the Junos OS?
- A. 0
- B. 1
- C. 2
- D. 3
正解：D
解説：
In Junos OS, the default route preference for a static route is 5. Route preference values are used to determine which route should be installed in the routing table when multiple routes to the same destination are available.
Step-by-Step Breakdown:
Static Route Preference:
A static route, by default, has a preference of 5, making it a highly preferred route. Lower preference values are more preferred in Junos, meaning static routes take precedence over most dynamic routing protocol routes, such as OSPF (preference 10) or BGP (preference 170).
Route Preference:
Route preference is a key factor in the Junos routing decision process. Routes with lower preference values are preferred and installed in the forwarding table.
Juniper Reference:
Static Routes: In Junos, the default preference for static routes is 5, making them more preferred than most dynamic routes.
質問 # 85
What does VXLAN stand for in the context of EVPN/VXLAN?
- A. Very Extended Virtual LAN
- B. Virtualized Ethernet VPN
- C. Virtual Extensible VLAN
- D. Virtual X-Series LAN
正解：C
質問 # 86
You want to enable a Junos device to support aggregated Ethernet interfaces. In this scenario, which configuration hierarchy would you use?
- A. [edit interfaces]
- B. [edit chassis]
- C. [edit switch-options]
- D. [edit system]
正解：B
解説：
To configure aggregated Ethernet (AE) interfaces on a Junos device, the configuration is done under the [edit chassis] hierarchy.
Step-by-Step Breakdown:
Chassis Configuration:
The chassis configuration is responsible for enabling the hardware to support Link Aggregation Groups (LAGs), allowing multiple physical interfaces to be bundled into a single logical interface for load balancing and redundancy.
Command Example:
set chassis aggregated-devices ethernet device-count <number>
This command enables a specific number of aggregated Ethernet interfaces on the device.
Juniper Reference:
LAG Configuration in Junos: The chassis hierarchy is used to allocate and manage hardware resources for aggregated Ethernet interfaces in Juniper devices.
質問 # 87
Which two statements are true with regards to MACsec?
- A. It does not provide encryption for an Ethernet traffic between two network nodes.
- B. It provides authentication for an Ethernet traffic between two network nodes.
- C. It does not provide authentication for an Ethernet traffic between two network nodes.
- D. It provides encryption for an Ethernet traffic between two network nodes.
正解：B、D
質問 # 88
What are two consequences of having all network devices in a single collision domain? (Choose two.)
- A. The amount of network resource consumption is increased.
- B. The amount of network resource consumption does not change.
- C. The chance of packet collision is decreased.
- D. The chance of packet collision is increased.
正解：A、D
解説：
A collision domain is a network segment where data packets can "collide" with one another when being sent on the same network medium.
Step-by-Step Breakdown:
Increased Collision Probability:
If all devices are in a single collision domain, the likelihood of packet collisions increases as more devices attempt to send packets simultaneously, leading to network inefficiencies. Increased Resource Consumption:
More collisions result in increased network resource consumption as devices need to retransmit packets, causing higher utilization of bandwidth and slowing down network performance. Juniper Reference: Collision Domains: Proper network segmentation using switches reduces collision domains, thereby improving network performance and reducing packet collisions.
質問 # 89
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