Juniper JN0-280 Online Practice Questions and Exam Preparation

Juniper JN0-280 Online Questions & Answers

• Question 121:

  How does OSPF calculate the best path to a particular prefix?

  A. It finds the path with the numerically lowest cost.
  B. It finds the path with the shortest autonomous system path.
  C. It finds the path with the least number of hops.
  D. It finds the path with the numerically lowest route preference.
  A. It finds the path with the numerically lowest cost.

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  Explanation/Reference:

  OSPF (Open Shortest Path First)calculates the best path based on the cost of the route, which is derived from the bandwidth of the interfaces along the path.

  Step-by-Step Breakdown:

  OSPF Path Selection:

  OSPF assigns a cost to each link, typically based on the link's bandwidth (higher bandwidth equals lower cost).

  The OSPF algorithm computes the shortest path to a destination by adding the costs of all links in the path. The path with the numerically lowest total cost is chosen as the best path.

  Cost Calculation:The OSPF cost can be manually adjusted or automatically calculated using the default formula:

  Cost=Reference BandwidthLink Bandwidth\text{Cost} = \frac{\text{Reference Bandwidth}}{\text{Link Bandwidth}}Cost=Link BandwidthReference Bandwidth

  Juniper Reference:

  OSPF Best Path Selection: OSPF selects the path with the lowest cumulative cost, ensuring efficient use of higher-bandwidth links in Junos networks.

• Question 122:

  Referring to the exhibit, which statement is correct?

  

  A. The ge-0/0/0 interface has been explicitly assigned to a VLAN named default.
  B. The default VLAN is a user defined VLAN name.
  C. The asterisk indicates that the interface is active.
  D. The ge-0/0/12 interfaces is an access port.
  C. The asterisk indicates that the interface is active.

• Question 123:

  Which statement is correct about the BGP AS path when advertising routes?

  A. The order of the AS path is not significant.
  B. The local AS number is added to the end of the AS path.
  C. The order of the AS path is only significant in IBGP.
  D. The local AS number is added to the beginning of the AS path.
  D. The local AS number is added to the beginning of the AS path.

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  Explanation/Reference:

  The BGP AS (Autonomous System) path attribute is crucial in path selection and loop prevention. Each BGP router appends its local AS number to the beginning of the AS path when it advertises a route to an external BGP (eBGP) peer.

  Step-by-Step Breakdown:

  AS Path Attribute:The AS path is a sequence of AS numbers that a route has traversed to reach a destination. Each AS adds its number to the front of the path, allowing BGP to track the route's history. Why the Local AS is Added at the

  Beginning:When advertising a route to an eBGP neighbor, a BGP router adds its own AS number to the beginning of the AS path. This ensures that the AS path reflects the route's journey accurately from the origin to the destination, and

  prevents loops in BGP. If the route returns to the same AS, the router will detect its AS number in the path and reject the route, preventing routing loops. Order of the AS Path:The order is significant because BGP uses it to select the best

  path. A shorter AS path is preferred, as it indicates fewer hops between the source and destination.

  Juniper Reference:

  AS Path Attribute: Junos devices append the local AS at the start of the AS path before advertising the route to an external peer.

• Question 124:

  Which statement is correct about the OSPF link-state database?

  A. Each router within the same area must maintain a unique copy of the link-state database.
  B. Each router within the same area must maintain an identical copy of the link-state database.
  C. Each router within the OSPF domain must maintain a unique copy of the link-state database.
  D. Each router within the OSPF domain must maintain an identical copy of the link-state database.
  A. Each router within the same area must maintain a unique copy of the link-state database.

• Question 125:

  Which of the following is an important consideration when configuring BFD?

  A. Setting a very high multiplier to avoid false positiveswrong
  B. Using the same BFD interval on all devices in the network
  C. Adjusting the BFD interval and multiplier according to network needs
  D. Disabling all other failure detection mechanisms
  C. Adjusting the BFD interval and multiplier according to network needs

• Question 126:

  Filter-based forwarding is typically used to:

  A. Increase the security of the routing process.
  B. Implement policy-based routing decisions.
  C. Optimize the routing table size.
  D. Automatically generate routing entries.
  B. Implement policy-based routing decisions.

• Question 127:

  What is the first route selection mechanism for IBGP?

  A. as path
  B. MED
  C. local preference
  D. origin
  C. local preference

• Question 128:

  Which two prefixes are contributing routes to a 10.20.0.0/18 aggregate route? (Choose two)

  A. 10.20.0.0/24
  B. 10.20.60.0/23
  C. 10.20.0.0/16
  D. 10.20.100.0/24
  A. 10.20.0.0/24
  B. 10.20.60.0/23

• Question 129:

  In troubleshooting a Virtual Chassis setup, what is a common issue to look for?

  A. Incompatible software versions between member switches
  B. Too many switches in a single Virtual Chassis configuration
  C. Use of copper cables for inter-switch connections
  D. Activation of all ports for Virtual Chassis connections
  A. Incompatible software versions between member switches

• Question 130:

  What information in the Ethernet header is used to populate the bridging table?

  A. destination address
  B. source address
  C. type
  D. protocol
  B. source address

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  Explanation/Reference:

  The source MAC address in the Ethernet header is used to populate the bridging table (also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with

  the ingress port in its MAC address table.

  Step-by-Step Breakdown:

  Learning Process:When an Ethernet frame arrives on a switch port, the switch looks at thesource MAC address and adds this MAC address to the MAC table along with the port it was received on.

  This process is called MAC learning .

  Purpose:The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding.

  Juniper Reference:

  Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.