5.4.3 Network Layer Quiz Answers

Networking Devices and Initial Configuration Module 5.4.3 Network Layer Quiz Answers

1. Which value, that is contained in an IPv4 header field, is decremented by each router that receives a packet?

  • Differentiated Services
  • Fragment Offset
  • Header Length
  • Time-to-Live

Explanation: When a router receives a packet, the router will decrement the Time-to-Live (TTL) field by one. When the field reaches zero, the receiving router will discard the packet and will send an ICMP Time Exceeded message to the sender.

2. Which statement accurately describes a characteristic of IPv4?

  • All IPv4 addresses are assignable to hosts.
  • IPv4 has a 32-bit address space.
  • An IPv4 header has fewer fields than an IPv6 header has.
  • IPv4 natively supports IPsec.

Explanation: IPv4 has a 32-bit address space, providing 4,294,967,296 unique addresses, but only 3.7 billion are assignable, a limit due to address reservation for multicasting and testing. IPv4 does not provide native support for IPsec. IPv6 has a simplified header with fewer fields than IPv4 has.

3. Which technology provides a solution to IPv4 address depletion by allowing multiple devices to share one public IP address?

  • ARP
  • DNS
  • NAT
  • SMB
  • DHCP
  • HTTP

Explanation: Network Address Translation (NAT) is a technology implemented within IPv4 networks. One application of NAT is to use a few public IP addresses to be shared by many internal network hosts which use private IP addresses. NAT removes the need for public addresses for every internal host. It therefore provides a solution to slow down the IPv4 address depletion.

4. Why is IPv6 designed to replace IPv4?

  • because most computers have a 64-bit processor
  • because the IPv4 address space will soon be depleted
  • to allow computers to address more memory
  • to address compatibility issues with mobile devices

Explanation: Various projections show that by 2015 to 2020, there will be no free public IPv4 addresses available.

5. Which characteristic of the network layer in the OSI model allows carrying packets for multiple types of communications among many hosts?

  • the de-encapsulation of headers from lower layers
  • the selection of paths for and direct packets toward the destination
  • the ability to operate without regard to the data that is carried in each packet
  • the ability to manage the data transport between processes running on hosts

Explanation: The function of the network layer protocols specifies the packet structure and processing used to carry the data from one host to another host. The actual communication data is encapsulated in the network layer PDU. The feature of its operation without regard to the data carried in each packet allows the network layer to carry packets for multiple types of communications.

6. Which statement describes a characteristic of the network layer in the OSI model?

  • It manages the data transport between the processes running on each host.
  • In the encapsulation process, it adds source and destination port numbers to the IP header.
  • When a packet arrives at the destination host, its IP header is checked by the network layer to determine where the packet has to be routed.
  • Its protocols specify the packet structure and processing used to carry the data from one host to another.

Explanation: The transport layer manages the data transport between the processes that are running on each host. In the encapsulation process, the network layer adds the IP header information, such as the IP address of the source (sending) and destination (receiving) hosts. When a packet arrives at the network layer of the destination host, the host checks the IP header of the packet to verify if the destination IP address within the header matches its own IP address.

7. Which layer of the OSI model is responsible for the logical addressing of packets?

  • data link
  • network
  • session
  • transport

Explanation: The network layer is the layer that consists of packets containing logical (IP) addressing.

8. What is the order of encapsulation for the protocol data units passing from the user application down the stack?

  • bits, segments, packets, frames, data
  • data, segments, packets, frames, bits
  • segments, data, packets, frames, bits
  • segments, packets, frames, bits, data

Explanation: The correct order of encapsulation of protocol data units down the protocol stack is as follows:

  • data
  • segments
  • packets
  • frames
  • bits

9. What process involves placing one PDU inside of another PDU?

  • encapsulation
  • encoding
  • segmentation
  • flow control

Explanation: When a message is placed inside of another message, this is known as encapsulation. On networks, encapsulation takes place when one protocol data unit is carried inside of the data field of the next lower protocol data unit.

10. What information is added during encapsulation at OSI Layer 3?

  • source and destination MAC
  • source and destination application protocol
  • source and destination port number
  • source and destination IP address

Explanation: IP is a Layer 3 protocol. Layer 3 devices can open the Layer 3 header to inspect the Layer 3 header which contains IP-related information including the source and destination IP addresses.

11. How does the network layer use the MTU value?

  • The network layer depends on the higher level layers to determine the MTU.
  • The network layer depends on the data link layer to set the MTU, and adjusts the speed of transmission to accommodate it.
  • The MTU is passed to the network layer by the data link layer.
  • To increase speed of delivery, the network layer ignores the MTU.

Explanation: The data link layer indicates to the network layer the MTU for the medium that is being used. The network layer uses that information to determine how large the packet can be when it is forwarded. When packets are received on one medium and forwarded on a medium with a smaller MTU, the network layer device can fragment the packet to accommodate the smaller size.

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