Juniper JN0-280 Online Practice Questions and Exam Preparation

Juniper JN0-280 Online Questions & Answers

• Question 21:

  VLANs help in reducing which of the following? (Choose two)

  A. Collision domains
  B. Broadcast domains
  C. Routing complexity
  D. Encryption requirements
  A. Collision domains
  B. Broadcast domains

• Question 22:

  When troubleshooting an OSPF neighborship, you notice that the router stopped at the ExStart state. What is the cause of this result?

  A. The priority is set to 255.
  B. There is an interval timing mismatch.
  C. There is an area ID mismatch.
  D. There is an MTU mismatch.
  D. There is an MTU mismatch.

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  Explanation/Reference:

  When an OSPF (Open Shortest Path First) neighborship is stuck in the ExStart state, it usually points to a mismatch in Maximum Transmission Unit (MTU) settings between two routers trying to establish the adjacency. The ExStart state is

  where OSPF routers negotiate the master-slave relationship and exchange DBD (Database Description) packets.

  Step-by-Step Breakdown:

  OSPF Neighbor States: OSPF goes through several states to establish an adjacency with a neighbor:

  Down: No hello packets have been received.

  Init: Hello packets are received, but bidirectional communication isn't confirmed.

  2-Way: Bidirectional communication is established.

  ExStart: The routers are negotiating who will be the master and who will be the slave, and begin to exchange DBD packets.

  Exchange: The routers start exchanging the database information.

  Loading: The routers process the Link-State Advertisements (LSAs).

  Full: The adjacency is fully established.

  MTU Mismatch Issue:During the ExStart state, both OSPF routers must agree on their MTU values. If there is an MTU mismatch between the two routers, OSPF neighbors will fail to move from the ExStart to the Exchange state. The router

  with the larger MTU setting will not accept DBD packets from the router with a smaller MTU because the packets may exceed the smaller MTU size.

  In Juniper devices, this behavior can be identified by examining the MTU settings using the show interfaces command and ensuring both routers have matching MTU configurations. To resolve this issue, either match the MTU settings on both

  routers or configure OSPF to ignore MTU mismatches using the command set protocols ospf ignore-mtu.

  Juniper Reference:

  Junos Command: show ospf neighbor helps diagnose neighbor states.

  MTU Adjustment: set interfaces mtu can be used to set the MTU values correctly.

• Question 23:

  You are creating an IP fabric underlay and want to use OSPF as your routing protocol.

  In this scenario, which statement is correct?

  A. All leaf devices must be configured in separate OSPF areas.
  B. All leaf and spine devices must be the same model to ensure the proper load-balancing behavior.
  C. Interface speeds should be the same throughout the fabric to ensure that all links are utilized.
  D. All spine devices must use the same router ID.
  C. Interface speeds should be the same throughout the fabric to ensure that all links are utilized.

  ---

  Explanation/Reference:

  When creating an IP fabric underlay using OSPF as the routing protocol, consistent interface speeds are important to ensure optimal traffic distribution and utilization of all links.

  Step-by-Step Breakdown:

  OSPF and Interface Speeds:OSPF calculates the cost of a link based on its bandwidth.

  The default cost calculation in OSPF is:

  

  If interface speeds vary significantly, OSPF may choose paths with lower cost (higher bandwidth), resulting in some links being underutilized. Equal Utilization:To ensure that all links are equally utilized in an IP fabric, it is recommended to

  maintain uniform interface speeds across the fabric. This ensures balanced load sharing across all available paths.

  Juniper Reference:

  IP Fabric with OSPF: Juniper recommends consistent interface speeds to maintain even traffic distribution and optimal link utilization in IP fabric underlay designs.

• Question 24:

  Which Junos OS routing table stores IPv6 addresses?

  A. inet.0
  B. inet0.6
  C. inet.6
  D. inet6.0
  D. inet6.0

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  Explanation/Reference:

  In Junos OS, routing information is stored in different routing tables depending on the protocol and address family. For IPv6 addresses, the routing table used is inet6.0 .

  Step-by-Step

  Routing Tables in Junos:

  inet.0: This is the primary routing table for IPv4 unicast routes.

  inet6.0: This is the primary routing table for IPv6 unicast routes.

  inet.3: This routing table is used for MPLS-related routing.

  Other routing tables, like inet.1, inet.2, are used for multicast and other specific purposes.

  inet6.0 Routing Table:When IPv6 is enabled on a Juniper router, all the IPv6 routes are stored in the inet6.0 table. This includes both direct routes (connected networks) and learned routes (from dynamic routing protocols like OSPFv3, BGP,

  etc.).

  Verification:To view IPv6 routes, the command show route table inet6.0 is used. This will display the contents of the IPv6 routing table, showing the network prefixes, next-hop addresses, and protocol information for each route.

  Juniper Reference:

  Junos Command: Use show route table inet6.0 to check IPv6 routing entries.

  IPv6 Routing: Ensure that the IPv6 protocol is enabled on interfaces and that routingprotocols like OSPFv3 or BGP are properly configured for IPv6 traffic handling.

• Question 25:

  Which Junos operational mode command is used to troubleshoot issues with VLANs?

  A. show vlans
  B. monitor traffic
  C. show ethernet-switching table
  D. show interfaces
  C. show ethernet-switching table

• Question 26:

  In the context of Layer 2 switching, what does RSTP stand for?

  A. Rapid Spanning Tree Protocol
  B. Routing Switch Transport Protocol
  C. Redundant Switching Tree Protocol
  D. Resilient Switching Transport Protocol
  A. Rapid Spanning Tree Protocol

• Question 27:

  Referring to the 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 ignores the update from R1.
  B. R2 does nothing with R3's update.
  C. R2 ignores the update from R3.
  D. R2 acknowledges R3 and discards it.
  C. R2 ignores the update from R3.

  ---

  Explanation/Reference:

  In the exhibit, R2 receives the same OSPF update from both R1 and R3. OSPF has mechanisms toprevent 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 willignore 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.

• Question 28:

  How does VLAN tagging benefit network segmentation?

  A. By encrypting data traffic between VLANs
  B. By ensuring the same IP address range can be used in different VLANs.
  C. By enabling the identification and separation of traffic belonging to different VLANs.
  D. By providing a backup path for data in case of link failure.
  D. By providing a backup path for data in case of link failure.

• Question 29:

  Which statement about switches is correct?

  A. Each port is a member of VLAN 2 by default.
  B. Every port is in a unique collision domain.
  C. Each port is in a unique broadcast domain by default.
  D. All ports reside in the same collision domain.
  B. Every port is in a unique collision domain.

  ---

  Explanation/Reference:

  Each port on a modern switch creates a separate collision domain . This allows multiple devices to communicate simultaneously without collisions on different ports.

  Step-by-Step Breakdown:

  Collision Domain:

  A collision domain is a network segment where data packets can collide if two devices send packets simultaneously.

  On a switch, each port creates a separate collision domain , so collisions only occur if two devices connected to the same port (through a hub, for instance) try to send data at the same time. Switches vs Hubs:Unlike hubs, which have one

  large collision domain, switches isolate collisions to individual ports, improving performance.

  Juniper Reference:

  Switch Port Behavior: In Juniper switches, each port operates in its own collision domain, enhancing network efficiency by reducing the chances of packet collisions.

• Question 30:

  What is the default route preference of a static route in the Junos OS?

  B. 10
  C. 1
  D. 5
  D. 5

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  Explanation/Reference:

  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.