2101 Ch08: Networking Layer Overview and Functions
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Questions and Answers

What is the primary role of a router in the network layer?

  • To encapsulate the protocol data unit from the transport layer
  • To establish a connection between local devices
  • To process packets at the destination host
  • To select the best path and direct packets towards a destination host (correct)

    • Which operation involves adding IP header information such as source and destination addresses?

  • De-encapsulation
  • Addressing
  • Routing
  • Encapsulation (correct)

    • What unique information must end devices have for identification on the network?

  • Routing number
  • IP address (correct)
  • Subnet mask
  • MAC address

    • How is packet forwarding accomplished in a network?

    <p>Through the use of network layer protocols and routing</p> Signup and view all the answers

    What describes the term 'hop' in the context of network routing?

    <p>A single router encountered by a packet on its way to the destination</p> Signup and view all the answers

    Why is it necessary for a packet to be routed by multiple routers?

    <p>To reach different subnets effectively as packets traverse networks</p> Signup and view all the answers

    Which protocol is NOT considered a network layer communication protocol?

    <p>Transmission Control Protocol (TCP)</p> Signup and view all the answers

    What is the first step that occurs when a packet arrives on a router interface?

    <p>The router examines the destination IPv4 address.</p> Signup and view all the answers

    What does the IPv6 route table list?

    <p>All known IPv6 routes.</p> Signup and view all the answers

    What is one major difference between static and dynamic routing?

    <p>Dynamic routing automatically adjusts to network changes.</p> Signup and view all the answers

    Which type of route entry indicates a network directly connected to the router?

    <p>Directly-connected route</p> Signup and view all the answers

    In the packet forwarding process, what happens after the router examines the destination IP address?

    <p>The router searches for the best matching route.</p> Signup and view all the answers

    How does a router determine the 'best' route to forward a packet?

    <p>By choosing the longest matching prefix.</p> Signup and view all the answers

    What types of networks do directly-connected route entries represent?

    <p>Any network interface that is active and configured.</p> Signup and view all the answers

    What do routing tables in routers primarily store?

    <p>All known network addresses and route entries.</p> Signup and view all the answers

    What is the default destination for packets sent to a remote network?

    <p>The default gateway, typically the local router.</p> Signup and view all the answers

    What type of routing entry indicates a manually configured route by an administrator?

    <p>S</p> Signup and view all the answers

    Which of the following correctly defines the characteristic of IP being connectionless?

    <p>No dedicated end-to-end connection is established.</p> Signup and view all the answers

    What distinguishes an IPv6 packet header from an IPv4 packet header?

    <p>IPv6 eliminates the need for NAT.</p> Signup and view all the answers

    During the packet forwarding process, what initial action does a router take upon receiving a packet?

    <p>Examines the destination IP address.</p> Signup and view all the answers

    Which operation is NOT one of the basic functions performed by network layer protocols?

    <p>Compression of data</p> Signup and view all the answers

    What does the 'D' code signify in routing information?

    <p>Dynamic routing protocol (EIGRP)</p> Signup and view all the answers

    Which of the following statements is true regarding the packet structure defined by IPv4?

    <p>IPv4 headers contain a header checksum field.</p> Signup and view all the answers

    What does the IPv6 address space improvement address specifically?

    <p>Depletion of IPv4 addresses</p> Signup and view all the answers

    What is a characteristic of OSPF within the context of network layer protocols?

    <p>It is a dynamic routing protocol for larger networks.</p> Signup and view all the answers

    Study Notes

    Network Layer Overview

    • The network layer (OSI Layer 3) is responsible for communication protocols and routing protocols.
    • Routers are used to forward data between networks.
    • Key network layer protocols include Internet Protocol version 4 (IPv4), Internet Protocol version 6 (IPv6), Open Shortest Path First (OSPF), and Internet Control Message Protocol (ICMP).

    Network Layer Functions

    • Addressing end devices: Each device must have a unique IP address for identification.
    • Encapsulation: The network layer encapsulates data from the transport layer into a packet by adding an IP header, which includes source and destination IP addresses.
    • Routing: Routers use routing tables to determine the best path to forward packets to their destination.
    • De-encapsulation: When a packet arrives at the destination host, the IP header is removed.

    Network Layer Characteristics

    • IPv4 and IPv6 are the primary network layer communication protocols.
    • IP is connectionless, meaning no dedicated connection is established before transmitting data.
    • IP is best-effort, meaning it does not guarantee delivery of all packets.
    • IP is media-independent, meaning it operates independently of the underlying physical network.

    IPv4 Packet Structure

    • The IPv4 header contains fields with binary values that specify packet settings.
    • Key fields include: version, DS, header checksum, TTL, protocol, source IP address, and destination IP address.

    IPv6 Packet Structure

    • IPv6 was designed to address IPv4 limitations such as address depletion and network complexity.
    • Key fields include: version, traffic class, flow label, payload length, next header, hop limit, source IPv6 address, and destination IPv6 address.

    Host Routing

    • Hosts use routing tables to determine where to send packets.
    • The netstat -r (or route print) command displays the host's routing table.
    • The routing table lists all known routes, including direct connections, local network, and default routes.

    Router Operations

    • Routers also contain routing tables, which are used to forward packets based on destination IP addresses.
    • The router's routing table includes routes for directly-connected networks, statically configured routes, and routes learned from routing protocols like OSPF.
    • Routers forward packets based on the best (longest) matching route entry.

    Routing Table Entries

    • Directly-connected networks: These routes represent active router interfaces.
    • Static routes: These routes are manually configured.
    • Dynamic routes: These routes are learned using routing protocols.

    Data Encapsulation and De-encapsulation

    • The process of encapsulating data at each layer allows for independent development and scaling.
    • The transport layer PDU is encapsulated into an IP packet by adding an IP header.
    • Routers and Layer 3 switches examine the IP header as the packet travels across the network.
    • IP addressing remains unchanged throughout the network, except when NAT is used.

    Network Address Translation (NAT)

    • NAT is a mechanism for translating network addresses from one format to another.
    • NAT is commonly used to conserve IPv4 addresses.
    • NAT is discussed in later modules.

    Router Operations

    • Routers use routing protocols to determine the best path for packets.
    • The network layer addressing (IP address) is examined by routers for packet forwarding.
    • The data portion of the packet remains unchanged during network layer processing.

    IP Protocol Design

    • IP was designed for low overhead, providing only the necessary functions for packet delivery.
    • IP is not designed to track or manage the flow of individual packets.

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    Related Documents

    2101-Ch08.docx

    Description

    This quiz covers the essential functions and characteristics of the network layer, which is the third layer of the OSI model. Key topics include addressing, encapsulation, routing, and the primary protocols like IPv4 and IPv6. Test your knowledge on how routers facilitate communication between networks.

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