JNCIE-DC free practice test

All questions and explanations

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1. Question 1

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   What is the primary purpose of a spine-leaf topology in a data center network?

   1. To provide non-blocking, high-bandwidth east-west connectivity

   2. To replace core-distribution-aggregation layers with a single device

   3. To prioritize north-south traffic over east-west traffic

   4. To simplify management by using only Layer 2 forwarding

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   • To provide non-blocking, high-bandwidth east-west connectivity

   Spine-leaf designs create a Clos network that delivers uniform latency and high bisection bandwidth between any leaf switches. This architecture is optimized for server-to-server communication within the data center.

2. Question 2

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   Which routing protocol is commonly used between spine and leaf devices in an underlay network?

   1. OSPF

   2. BGP

   3. IS-IS

   4. RIP

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   • IS-IS

   IS-IS is frequently chosen for underlay routing in large-scale data centers due to its scalability and efficiency in handling flat anycast topologies. It supports fast convergence and integrates well with EVPN overlays.

3. Question 3

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   What does VXLAN stand for in the context of data center networking?

   1. Virtual eXtensible Local Area Network

   2. Virtualized eXternal Link Access Network

   3. Virtual eXchange Layer Aggregation Node

   4. Virtual eXtended Link Overlay Network

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   • Virtual eXtensible Local Area Network

   VXLAN is a network virtualization technology that encapsulates Layer 2 frames within Layer 3 UDP packets to extend Layer 2 segments across Layer 3 boundaries. It helps overcome VLAN ID limitations and supports multi-tenancy.

4. Question 4

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   Which feature is used to synchronize time across all devices in a Juniper data center switch?

   1. NTP

   2. PTP

   3. SNMP

   4. Syslog

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   • NTP

   Network Time Protocol (NTP) is used to ensure all devices share a consistent time reference, which is critical for logging, troubleshooting, and coordinated operations. Precision Time Protocol (PTP) is also supported for sub-microsecond accuracy in specific applications.

5. Question 5

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   What is the role of an EVPN control plane in a Juniper data center solution?

   1. To distribute MAC and IP reachability information across the fabric

   2. To encrypt traffic between spine and leaf devices

   3. To replace the need for Layer 3 gateways

   4. To manage physical cable connections between devices

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   • To distribute MAC and IP reachability information across the fabric

   Ethernet VPN (EVPN) uses BGP to advertise MAC and IP prefixes, enabling efficient host mobility and redundancy without relying on flooding. It provides a scalable control plane for Layer 2 and Layer 3 services in the data center.

6. Question 6

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   Which command would you use to check the status of a physical interface on a Juniper switch?

   1. show interfaces terse

   2. display interface status

   3. check interface operational

   4. list interfaces brief

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   • show interfaces terse

   The operational command 'show interfaces terse' provides a concise overview of interface states, including link status and error counters. This is a common troubleshooting step for verifying physical connectivity.

7. Question 7

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   What does the term 'anycast gateway' refer to in a data center network?

   1. A single IP address shared by multiple devices for redundancy

   2. A gateway that supports both IPv4 and IPv6 simultaneously

   3. A gateway located in any geographic location

   4. A gateway that routes traffic to the least loaded server

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   • A single IP address shared by multiple devices for redundancy

   Anycast gateway allows multiple devices to share the same IP address, typically used for default gateways in Layer 3 host communication. The network directs hosts to the nearest or most appropriate device providing the service.

8. Question 8

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   Which protocol is used for host reachability and MAC address advertisement in an EVPN-based data center?

   1. BGP

   2. OSPF

   3. IS-IS

   4. RIP

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   • BGP

   BGP is the protocol used to carry EVPN routes, including MAC and IP reachability information, across the fabric. This allows for efficient host learning and mobility without relying on Layer 2 flooding.

9. Question 9

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   What is the purpose of a link aggregation group (LAG) in a data center switch?

   1. To combine multiple physical links into a single logical link for increased bandwidth and redundancy

   2. To isolate broadcast domains between different VLANs

   3. To provide a dedicated management path separate from user traffic

   4. To replace the need for routing protocols in the underlay

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   • To combine multiple physical links into a single logical link for increased bandwidth and redundancy

   LAG bundles multiple physical ports to act as a single logical connection, improving throughput and providing failover in case of a link failure. It is commonly used between servers and switches or between switches.

10. Question 10

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    Which feature enables a Juniper switch to automatically detect and classify traffic applications?

    1. Application Recognition (App-ID)

    2. Flow Monitoring (sFlow)

    3. NetFlow Export

    4. Port Mirroring (SPAN)

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    • Application Recognition (App-ID)

    Application Recognition, often referred to as App-ID, allows the device to identify applications regardless of port number, enabling policy enforcement based on application type rather than just port usage.

11. Question 11

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    What is the primary benefit of using VLANs in a data center network?

    1. To logically segment traffic and improve security and manageability

    2. To increase the physical speed of network links

    3. To eliminate the need for routing between subnets

    4. To replace the need for firewalls

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    • To logically segment traffic and improve security and manageability

    VLANs provide logical segmentation of broadcast domains, which enhances security by isolating traffic and simplifies management by grouping devices with similar requirements. This is essential in multi-tenant data center environments.

12. Question 12

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    Which command is used to view the MAC address table on a Juniper switch?

    1. show mac table

    2. display mac-learning

    3. show l2fib extensive

    4. list arp entries

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    • show l2fib extensive

    The command 'show l2fib extensive' displays the Layer 2 forwarding information base, including MAC addresses learned on each interface. This is useful for troubleshooting connectivity and host placement within the network.

13. Question 13

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    What does STP stand for in the context of Ethernet networks?

    1. Spanning Tree Protocol

    2. Shortest Tree Path

    3. Secure Transport Protocol

    4. Switch Trunking Protocol

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    • Spanning Tree Protocol

    Spanning Tree Protocol prevents loops in Layer 2 networks by logically disabling redundant paths while providing backup paths in case of link failure. Juniper switches support STP and its rapid variants like RSTP and MSTP.

14. Question 14

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    Which configuration element is required to enable inter-VLAN routing on a Juniper switch?

    1. VLAN interface with an IP address

    2. Physical interface assigned to a VLAN

    3. Static route to the VLAN subnet

    4. Dynamic routing protocol enabled globally

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    • VLAN interface with an IP address

    To route between VLANs, you must configure a VLAN interface (also known as a SVI) with an IP address and assign it to the appropriate VLAN. This provides a Layer 3 gateway for hosts in each VLAN.

15. Question 15

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    What is the purpose of a management plane in a network device?

    1. To handle device configuration, monitoring, and out-of-band management traffic

    2. To forward user data packets at wire speed

    3. To provide physical connectivity for console access

    4. To optimize data plane packet processing performance

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    Correct answer

    • To handle device configuration, monitoring, and out-of-band management traffic

    The management plane is responsible for device administration tasks such as SSH access, SNMP polling, and configuration changes. It is typically separated from the data plane to ensure control traffic does not interfere with user traffic.