Juniper JN0-280 Online Practice Questions and Exam Preparation

Juniper JN0-280 Online Questions & Answers

• Question 1:

  Referring to the exhibit,

  

  why are the BGP routes hidden?

  A. Load balancing is not enabled.
  B. There are too many hops to the destination.
  C. The BGP next hop is unreachable.
  D. Other routes are selected because of better metrics.
  C. The BGP next hop is unreachable.

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  Explanation/Reference:

  In the exhibit, the BGP routes are marked as hidden . This typically happens when the routes are not considered valid for use, but they remain in the routing table for reference. One common reason for BGP routes being hidden is that the next hop for these routes is unreachable.

  Step-by-Step Breakdown:

  BGP Next Hop:In BGP, when a route is received from a neighbor, the next hop is the IP address that must be reachable for the route to be used. If the next hop is unreachable (i.e., the router cannot find a path to the next-hop IP), the route is

  marked as hidden.

  Analyzing the Exhibit:The exhibit shows that the BGP next hop for all hidden routes is 10.4.4.4. If this IP is unreachable, the BGP routes from that neighbor will not be considered valid, even though they appear in the routing table.

  Verification:

  Use the command show route 10.4.4.4 to check if the next-hop IP is reachable.

  If the next-hop is not reachable, the BGP routes will be hidden. Resolving the next-hop reachability issue (e.g., fixing an IGP route or an interface) will allow the BGP routes to become active.

  Juniper Reference:

  Junos Command: show route hidden displays routes that are not considered for forwarding.

  Troubleshooting: Check the next hop reachability for hidden BGP routes using show route .

• Question 2:

  What happens if a frame with a known destination MAC address enters a switch?

  A. The egress PFE performs a MAC address lookup and determines the ingress PFE and port.
  B. The ingress PFE sends the header information to the R
  C. The ingress PFE performs a MAC address lookup and determines the egress PFE and port.
  D. The MAC address is added to the bridge table.
  C. The ingress PFE performs a MAC address lookup and determines the egress PFE and port.

• Question 3:

  In the context of Ethernet bridging on Junos devices, what is the purpose of the Spanning Tree Protocol (STP)?

  A. To prevent routing loops.
  B. To provide a mechanism for VLAN tagging.
  C. To prevent Layer 2 switching loops.
  D. To filter MAC addresses.
  C. To prevent Layer 2 switching loops.

• Question 4:

  Which two statements are about aggregated Ethernet bundles? (Choose two.)

  A. You must enable the chassis to support aggregated Ethernet interfaces.
  B. You must purchase a services license for the chassis to support aggregate Ethernet interfaces.
  C. You must specify which interfaces are members of a specific aggregated Ethernet bundle.
  D. You must enable LACP when configuring aggregated Ethernet bundles.
  A. You must enable the chassis to support aggregated Ethernet interfaces.
  C. You must specify which interfaces are members of a specific aggregated Ethernet bundle.

• Question 5:

  In the context of data center networking, what is the primary purpose of an Underlay Network?

  A. To provide a physical infrastructure for an Overlay Network.
  B. To handle external network connections exclusively.
  C. To facilitate virtual machine migrations.
  D. To encrypt data traffic between servers.
  A. To provide a physical infrastructure for an Overlay Network.

• Question 6:

  Which state in the adjacency process do OSPF routers check the MTU size?

  A. Init
  B. Exchange
  C. Done
  D. ExStart
  B. Exchange

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  Explanation/Reference:

  In OSPF, routers exchange link-state information in different stages to establish full adjacency. TheMTU size is checked during the Exchange state.

  Step-by-Step Breakdown:

  OSPF Adjacency Process:

  OSPF routers go through multiple stages when forming an adjacency: Down Init 2-Way ExStart , , , , Exchange Loading , , and Full .

  Exchange State:

  During the Exchange state, OSPF routers exchange Database Description (DBD) packets to describe their link-state databases. The MTU size is checked at this stage to ensure both routers can successfully exchange these packets without

  fragmentation.

  If there is an MTU mismatch , the routers may fail to proceed past the Exchange state.

  Juniper Reference:

  MTU Checking in OSPF: Junos uses the Exchange state to check for MTU mismatches, ensuring that routers can properly exchange database information without packet fragmentation issues.

• Question 7:

  Which two statements describe an IP fabric? (Choose two.)

  A. An IP fabric allows devices to always be one hop away.
  B. An IP fabric depends on Layer 2 switching.
  C. An IP fabric uses spine and leaf devices.
  D. An IP fabric provides traffic load sharing.
  C. An IP fabric uses spine and leaf devices.
  D. An IP fabric provides traffic load sharing.

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  Explanation/Reference:

  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.

• Question 8:

  What is the behavior of the default export policy for OSPF?

  A. Accept all routes.
  B. Reject all routes.
  C. Redistribute all routes.
  D. Forward all routes.
  B. Reject all routes.

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  Explanation/Reference:

  In Junos, the default export policy for OSPF is to reject all routes from being exported.

  Step-by-Step Breakdown:

  Default Export Policy:By default, OSPF in Junos does not export any routes to other routing protocols or neighbors. This is a safety mechanism to prevent unintended route advertisements.

  Custom Export Policies:

  If you need to export routes, you must create a custom export policy that explicitly defines which routes to advertise.

  Example: You can create an export policy to redistribute static or connected routes into OSPF.

  Juniper Reference:

  OSPF Export Behavior: In Juniper devices, the default policy for OSPF is to reject route advertisements unless explicitly configured otherwise through custom policies.

• Question 9:

  In the context of protocol-independent routing, what is the main difference between static and generated routes?

  A. Static routes require manual configuration, while generated routes are created dynamically.
  B. Static routes are used for load balancing, while generated routes are not.
  C. Generated routes support summarization, while static routes do not.
  D. Generated routes are manually configured, while static routes are automatically created.
  A. Static routes require manual configuration, while generated routes are created dynamically.

• Question 10:

  In the Junos OS, what is the default behavior of a switch when it receives a frame with an unknown destination MAC address?

  A. It discards the frame.
  B. It floods the frame out of all ports except the one it was received on.
  C. It sends the frame to its default gateway.
  D. It buffers the frame until the MAC address can be learned.
  B. It floods the frame out of all ports except the one it was received on.