DC Chapter 9

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Questions and Answers

What role do IP addresses play in the Internet?

  • They indicate the specific type of data being transmitted.
  • They determine the path a datagram takes through the network.
  • They identify the physical devices used in networking.
  • They define the exact points where source and destination hosts are connected. (correct)

What happens if the destination IP address in a datagram changes?

  • The datagram may still be rerouted correctly.
  • The packet never reaches its destination. (correct)
  • The packet will reach the destination without issues.
  • The source will receive an error message.

What is the purpose of link-layer addresses in a connectionless internetwork?

  • To facilitate communication at the data-link layer. (correct)
  • To identify the source and destination IP addresses.
  • To encapsulate data from the application layer.
  • To define the exact routing path for datagrams.

How are link-layer addresses also known?

<p>MAC addresses (B)</p> Signup and view all the answers

What happens to link-layer addresses when a frame moves from one link to another?

<p>They are changed. (A)</p> Signup and view all the answers

What is the primary efficiency gain when system A uses ARP to send datagrams to system B?

<p>Reduces the number of broadcast frames to be processed by other systems. (C)</p> Signup and view all the answers

How many broadcast frames does system A need to send to communicate with system B without using ARP if it has 10 datagrams?

<p>180 (C)</p> Signup and view all the answers

What occurs after system B responds to system A's ARP request?

<p>System A caches the link-layer address of system B. (C)</p> Signup and view all the answers

Which field in an ARP packet indicates the link-layer protocol type?

<p>Hardware type (C)</p> Signup and view all the answers

When using ARP, how many broadcast frames need to be processed by other systems compared to not using ARP?

<p>18 (A)</p> Signup and view all the answers

In the ARP packet format, what do the source and destination addresses define?

<p>The link-layer and network-layer addresses of sender and receiver (A)</p> Signup and view all the answers

What is one of the major drawbacks of processing broadcast frames in a network?

<p>It is inefficient, leading to increased network congestion. (B)</p> Signup and view all the answers

Which of the following best describes an ARP packet's encapsulation?

<p>Incorporated into a data-link frame with a specific payload indicator (D)</p> Signup and view all the answers

What is the primary function of the data-link layer at the source host?

<p>Encapsulate the datagram received from the network (D)</p> Signup and view all the answers

Which action does the data-link layer of intermediate nodes perform?

<p>Both encapsulate and decapsulate the datagram (A)</p> Signup and view all the answers

Why is encapsulation and decapsulation necessary at each intermediate node?

<p>Because links may use different protocols and frame formats (B)</p> Signup and view all the answers

How can the process of delivering a datagram in the Internet be compared to a traveler using different modes of transportation?

<p>The traveler must switch transportation modes at different stages. (A)</p> Signup and view all the answers

At which point does decapsulation occur for the destination host?

<p>At the destination node (C)</p> Signup and view all the answers

What does encapsulation involve at the data-link layer?

<p>Wrapping the datagram in additional protocol information (A)</p> Signup and view all the answers

What can be inferred about link-layer addresses in the context of encapsulation?

<p>They are typically different for each link in a transmission path. (C)</p> Signup and view all the answers

What role does the data-link layer play in relation to the network layer?

<p>It formats and prepares frames from datagrams for delivery. (A)</p> Signup and view all the answers

What is the main purpose of the ARP request in the communication process described?

<p>To translate IP addresses into MAC addresses. (D)</p> Signup and view all the answers

In the ARP packet structure, what does the 'Operation' field indicate?

<p>The action being requested (request or reply). (C)</p> Signup and view all the answers

Which address remains empty in the ARP request packet?

<p>Destination hardware address. (B)</p> Signup and view all the answers

What type of frame is used to send the ARP request from the source to the destination?

<p>Multicast frame. (D)</p> Signup and view all the answers

If the ARP request is sent by host with IP address N1, which address will it use as the source protocol address?

<p>The IP address N1. (D)</p> Signup and view all the answers

What does the hardware type of 0x0001 in the ARP packet indicate?

<p>Ethernet. (D)</p> Signup and view all the answers

What does the protocol type of 0x0800 signify in the ARP packet?

<p>Internet Protocol version 4. (C)</p> Signup and view all the answers

Which components of the ARP request are specific to the source host?

<p>Source hardware address and source protocol address. (B)</p> Signup and view all the answers

What does the data-link layer do upon receiving a frame at Router R1?

<p>Decapsulates the datagram and passes it to the network layer. (B)</p> Signup and view all the answers

What role does Router R1 play in the flow of packets?

<p>It decapsulates incoming frames and directs them to the appropriate layer. (B)</p> Signup and view all the answers

What information does the forwarding table at Router R1 contain?

<p>Network-layer addresses mapping to link-layer addresses. (D)</p> Signup and view all the answers

Which of the following layers is responsible for sending signals from Alice to Router R1?

<p>Physical layer (B)</p> Signup and view all the answers

What happens to the frame once it reaches the physical layer at Router R1?

<p>It is passed to the data-link layer. (D)</p> Signup and view all the answers

Which addresses are primarily used for communication at the network layer?

<p>Network-layer addresses (A)</p> Signup and view all the answers

What type of information does the ARP process utilize in Router R1?

<p>Maps network-layer addresses into data link-layer addresses. (A)</p> Signup and view all the answers

Which layer encapsulates the datagram into a frame for transmission to Router R1?

<p>Data-link layer (B)</p> Signup and view all the answers

What is the primary responsibility of the data-link layer?

<p>Creating and delivering frames to other nodes (A)</p> Signup and view all the answers

Which protocol is used to map an IP address to its corresponding link-layer address?

<p>Address Resolution Protocol (ARP) (A)</p> Signup and view all the answers

What do the terms 'nodes' and 'links' refer to in the context of the Internet?

<p>Hosts and networks respectively (C)</p> Signup and view all the answers

How does the data-link layer handle the flow of packets?

<p>By coordinating two data-link layers at the ends of a link (C)</p> Signup and view all the answers

What type of addressing is used to define the addresses of nodes that a packet should pass through?

<p>Link-layer addressing (D)</p> Signup and view all the answers

Which of the following activities is NOT part of the responsibilities of the data-link layer?

<p>Routing between networks (B)</p> Signup and view all the answers

Can two hosts in different networks share the same link-layer address?

<p>Yes, as link-layer addresses apply only to their local segment (B)</p> Signup and view all the answers

Is the size of the ARP packet fixed?

<p>No, they are defined by the link-layer protocol in use (C)</p> Signup and view all the answers

Flashcards

Link-layer Address

The unique identifier assigned to each device on a network, used at the data link layer for communication within a local network segment.

Link-layer Addressing

An addressing scheme used in connectionless networks like the internet, where datagrams can take different paths, requiring a mechanism to identify devices within a local network segment for communication.

Encapsulation

The process of adding the link-layer addresses to a datagram's header to create a frame, allowing the packet to be transmitted within a local network.

Data-link layer frame

A data-link layer frame contains the data-link layer addresses of the source and destination nodes, allowing communication within a specific network segment.

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Changing link-layer addresses during transmission

The link-layer addresses are changed when a datagram moves from one network segment to another, ensuring that packets are sent to the correct destination within each segment.

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Router

A network device responsible for forwarding data packets between networks. It acts as an intermediary along the path.

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Host

A network device that connects to the network, such as a computer or smartphone.

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Datagram

A single unit of data transmitted at the network layer, addressed to a specific destination.

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Frame

A unit of data transmitted at the data link layer, containing a datagram and its header.

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Encapsulation and Decapsulation at Intermediate Nodes

Each hop between two network nodes, commonly using different network protocols, requires both encapsulation and decapsulation.

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Reasons for Encapsulation and Decapsulation

Every link might use different protocols requiring encapsulation and decapsulation, even if they use the same protocol, different link-layer addresses necessitate this step.

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Encapsulation/Decapsulation

A process at each hop between two network nodes involving adding or removing specific header information to a datagram.

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Changing Link-Layer Address

The process of modifying the link-layer address of a datagram when it moves from one network to another.

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Forwarding Table

A table that stores mappings of network addresses to link-layer addresses, allowing routers to efficiently forward data packets.

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ARP (Address Resolution Protocol)

A mechanism used to discover the MAC address of a device on the same network when its IP address is known.

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ARP Request

When a host wants to send a packet to another device on the same network but doesn't know the destination's MAC address, it broadcasts an ARP request message.

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ARP Response

When a host responds with its MAC address to an ARP request, providing the requester with the information they need.

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Encapsulation in Networking

The process of wrapping a datagram within a data-link frame, adding link-layer addresses for transmission within a local network segment.

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Address Resolution

The process of determining a device's link-layer address, typically using ARP (Address Resolution Protocol), when the network-layer address is known.

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Network Packet with Multiple Datagrams

A single data packet containing multiple datagrams, allowing multiple data transfers together, reducing the overhead of sending multiple ARP frames.

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Why is ARP used?

The use of ARP to determine link-layer addresses before sending datagrams, optimizing network efficiency and reducing unnecessary broadcasts.

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ARP Broadcast

The procedure of sending ARP requests to all devices on a network segment to discover the link-layer address for a given network-layer address.

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ARP Unicast Response

An ARP response containing the sender's link-layer address, allowing a device to communicate directly with the intended recipient.

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Address Resolution Protocol (ARP)

A network layer protocol used to map IP addresses to their corresponding link-layer addresses, allowing devices to find each other within a network.

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Communication at the data-link layer

The process of transmitting data within a local network segment using the link-layer addresses of the source and destination devices.

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Communication at the network layer

The process of exchanging data packets between hosts or devices across different networks, using the network layer protocols.

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Study Notes

  • The TCP/IP protocol suite does not define protocols for the data-link or physical layers
  • These layers are part of the networks that make up the internet (wired/wireless)
  • Data-link layer protocols are standard protocols used in today's networks
  • The chapter gives a general overview of the data-link layer and common issues
  • Data-link layer relates to all types of networks
  • First section introduces the data-link layer, defining links and nodes
  • It lists and describes the services provided by this layer (point-to-point and broadcast)
  • Defines two sub-layers in the data-link layer, to be expanded on in later chapters
  • Explains the rationale behind the data-link layer addressing
  • Describes three types of link-layer addresses found in some protocols
  • Includes the Address Resolution Protocol (ARP), which connects network-layer addresses to data-link layer addresses
  • The data-link layer sits between the physical and network layers
  • Provides services to the network layer, and receives services from the physical layer
  • The data-link layer's responsibility is node-to-node packet delivery
  • Encapsulates network layer datagrams into frames, and decapsulates them
  • The source host encapsulates the datagram
  • Intermediate nodes encapsulate and decapsulate the datagram
  • The destination host decapsulates the datagram

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DC Chapter 9: Introduction to Data-Link Layer PDF

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