Network Layer Functions and Protocols Quiz
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Network Layer Functions and Protocols Quiz

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Questions and Answers

What is the primary function of forwarding in the network layer?

  • To evaluate network performance metrics
  • To plan the trip from source to destination
  • To encrypt data for security during transmission
  • To move packets from router’s input to an appropriate router output (correct)

    • What does routing determine in the context of network layer operations?

  • The route taken by packets from source to destination (correct)
  • The format for encapsulating data within datagrams
  • The specific IP address assigned to a host
  • The process of managing data link layers

    • Which of the following best describes what a router does with IP datagrams?

  • It generates new IP datagrams for each session.
  • It examines header fields in all IP datagrams passing through it. (correct)
  • It prioritizes traffic based on application type.
  • It encrypts them for secure transmission.

    • Which protocol is part of routing in the Internet?

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

    What is a characteristic of a connectionless service in networking?

    <p>Packets are routed independently without a predefined path</p> Signup and view all the answers

    What determines the end-to-end path through a network?

    <p>Routing algorithm</p> Signup and view all the answers

    What does VC stand for in the context of network services?

    <p>Virtual Circuit</p> Signup and view all the answers

    What does a forwarding table determine?

    <p>Local forwarding at the router</p> Signup and view all the answers

    Which of the following ATM classes does not guarantee any bandwidth?

    <p>ATM UBR</p> Signup and view all the answers

    In which architectures is connection setup an important function?

    <p>ATM, frame relay, and X.25</p> Signup and view all the answers

    What happens in the virtual circuit implementation before data can flow?

    <p>A call setup and teardown process occurs.</p> Signup and view all the answers

    How does the network layer differ from the transport layer in terms of connection service?

    <p>Network layer establishes connections between two hosts possibly with intervening routers</p> Signup and view all the answers

    In a datagram network, how are packets identified?

    <p>Each packet carries a destination host address</p> Signup and view all the answers

    Which of the following describes a service model allowing for guaranteed delivery?

    <p>Guaranteed delivery with less than 40 msec delay</p> Signup and view all the answers

    Which routing algorithm focuses on the complete view of the network?

    <p>Link state routing</p> Signup and view all the answers

    What is one type of restriction mentioned for network service models?

    <p>Restrictions on changes in inter-packet spacing</p> Signup and view all the answers

    Which characteristic differentiates connection-oriented services from connectionless services?

    <p>Connection-oriented services require dedicated paths.</p> Signup and view all the answers

    What value in the arriving packet's header would lead to the output link '1' in local forwarding?

    <p>1001</p> Signup and view all the answers

    What type of service does ATM ABR provide?

    <p>Guaranteed minimum bandwidth</p> Signup and view all the answers

    What is the primary function of the Internet network layer?

    <p>Path selection</p> Signup and view all the answers

    Which of the following is NOT a routing protocol mentioned?

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

    What does IP in the context of the network layer stand for?

    <p>Internet Protocol</p> Signup and view all the answers

    What does ICMP stand for in networking?

    <p>Internet Control Message Protocol</p> Signup and view all the answers

    The datagram format in IP includes which of the following?

    <p>Protocol version</p> Signup and view all the answers

    Which protocol is used for hierarchical routing?

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

    Which layer handles the forwarding process in networking?

    <p>Network layer</p> Signup and view all the answers

    What is the primary role of routing algorithms in a network?

    <p>Path selection</p> Signup and view all the answers

    Which of the following is a characteristic of 'link state' routing?

    <p>Forwarding based on entire network topology</p> Signup and view all the answers

    Study Notes

    Chapter 4: Network Layer

    • The slides are freely available to faculty, students, and readers.
    • The PowerPoint slides include animations and can be modified.
    • Use of the slides should mention their source.
    • Any posting of slides on a website must include a note about adapting the slides and copyright.
    • Authors of the slides are Jim Kurose and Keith Ross.

    Chapter Goals

    • Understand principles behind network layer services.
    • Understand network layer service models.
    • Understand forwarding versus routing.
    • Understand how routers operate.
    • Understand routing (path selection).
    • Understand broadcast, multicast, and instantiation, implementation in the internet.

    Chapter Outline

    • Introduction
    • Virtual circuit and datagram networks
    • What's inside a router
    • IP: Internet Protocol
      • Datagram format
      • IPv4 addressing
      • ICMP
      • IPv6
    • Routing algorithms
      • Link state
      • Distance vector
      • Hierarchical routing
    • Routing in the internet
      • RIP
      • OSPF
      • BGP
    • Broadcast and multicast routing
    • Network layer protocols and functions

    Network Layer

    • Transports segments from sending to receiving host
    • Encapsulates segments into datagrams
    • Delivers segments to the transport layer on receiving side
    • Network layer protocols are in every host and router.
    • Routers examine header fields in all IP datagrams passing through them

    Two Key Network Layer Functions

    • Forwarding: Moves packets from a router's input to appropriate output port.
    • Routing: Determines route taken by packets from source to destination.
    • Routing algorithms are used to determine routes.

    Interplay between Routing and Forwarding

    • The routing algorithm determines the end-to-end path through a network.
    • A forwarding table determines local forwarding at a router.
    • A header value in the packet's header is used to determine the output link.

    Connection Setup

    • A third important function in network architectures
    • Establish virtual connections before datagrams flow.
    • Routers get involved in connection setup in some architectures like ATM, frame relay or X.25.

    Network Service Model

    • Q: What service model for transporting datagrams from sender to receiver?
    • Individual datagrams: guaranteed delivery with less than 40 msec delay.
    • Flow of datagrams: in-order datagram delivery, minimum bandwidth guaranteed to a flow of datagrams, constraints on changes in inter packet spacing.

    Network Layer Service Models: Table

    • Attributes: network architecture, service model, bandwidth, loss, order, timing, congestion feedback
    • Examples of architectures and service models are shown (including Internet, ATM, CBR, VBR, ABR, and UBR).

    Virtual Circuits

    • The source-to-destination path behaves like a telephone circuit.
    • Performance is consistent and network resources are allocated in advance
    • Includes call setup & teardown ,VC identifier, and router state maintenance
    • Link-level and router resources can be allocated to virtual circuits.

    Virtual Circuits Implementation

    • Consists of path from source to destination
    • Contains VC numbers for each link along path
    • Creates entries in forwarding tables in routers.
    • Packets carry VC number rather than destination address.
    • VC number can change on each link based on forwarding table.

    Virtual Circuits: Signaling Protocols

    • Used to set up, maintain, and tear down VCs.
    • Used in ATM, frame relay and X.25 but are not used in the modern Internet.

    Datagram Networks

    • No call setup; no state about end-to-end connections in routers.
    • No network-level concept of connection.
    • Packets are forwarded using destination host address
    • Forwarding tables only look at destination address rather than maintaining connections.

    Datagram Forwarding Table

    • 4 billion IP addresses but rather than each one, lists ranges (aggregate table entries) for simplicity.
    • Routers use destination address in arriving packets to look up next hop using a forwarding table.
    • Longest prefix matching is used in the tables, and it finds the longest match for destination address within the table.

    Datagram or VC Networks: Why Choose One?

    • Internet (datagram): elastic service, many link types, different network characteristics, smart end systems (computers).
    • ATM (VC): evolved from telephony, strict timing and reliability requirements, need for guaranteed service, dumb end systems (telephones).

    Router Architecture Overview

    • Routing protocols (e.g., RIP, OSPF, BGP) run within the router, to compute and update forwarding tables and push it to input ports.
    • Routing processor (control plane)
    • High-speed switching fabric
    • Forwarding data plane (hardware)

    Input Port Functions

    • Physical layer: bit-level reception
    • Link layer (receive): receives frame and extracts the network-layer packet
    • Lookup: using forwarding table
    • Forwarding: Based on lookup
    • Queuing: to handle delay if packets come too quickly

    Switching Fabrics

    • Transfer packets from input buffer to appropriate output buffer.
    • Switching rate: Transfer rate of packets from inputs to outputs
    • Three types of fabrics: memory, bus, crossbar
    • Memory/CPU based switching
    • Bus switching
    • Interconnection Network switching (faster than bus)

    Switching via Memory

    • Packets are copied to system's memory.
    • Speed is limited by memory bandwidth.
    • 2 bus crossings need to occur for each datagram

    Switching via Bus

    • Datagrams from input port memory to output port memory via a shared bus.
    • Switching rate limited by bus bandwidth.
    • 32 Gbps bus sufficient speed for access, enterprise routers

    Switching via Interconnection Network

    • Allows overcoming bus limitations
    • Utilizes technologies like banyan networks, crossbars
    • It fragments datagram into smaller cells and switches cells through the fabric
    • Cisco 12,000 and above devices have this kind of architecture

    Output Ports

    • Buffer packets from the switching fabric.
    • Requires buffering to handle differences between the rate at which data flows from the fabric and the output ports
    • Queuing: if arriving rate exceeds output line speed.
    • Scheduling: how datagrams from the queue are processed.

    Input Port Queuing

    • Fabric slower; queueing at input queues could occur
    • Head-of-the-line blocking
    • Output Port Contention: only one packet is transferred at a time.

    Buffering

    • The recent recommendation is that the buffering amount at the output ports is proportional to the link capacity and the RTT (round trip time).

    ICMP

    • Internet Control Message Protocol
    • Used by hosts & routers to communicate network-level information.
    • ICMP messages (types and codes)
      • Error reporting
      • Echo request, reply

    IPv6 Motivation

    • Initial motivation: 32-bit address space exhaustion.
    • Additional motivation: header format helps processing/forwarding, header changes accommodate QoS.

    IPv6 Datagram Format

    • Fixed-length header (40 bytes)
    • No fragmentation allowed from the beginning.
    • Priority, flow label, next-header, hop limit, source, destination addresses in the header.

    Other Changes from IPv4

    • Removed checksums
    • Options outside the header
    • ICMPv6 with Packet Too Big messages
    • Multicast group management functions

    Transition from IPv4 to IPv6

    • Tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers.
    • Allows interoperability while IPv6 network deployment is still ongoing.

    Subnets

    • Subnets are isolated network islands.
    • Interfaces with same subnet portion of the IP address can communicate directly without requiring a router.

    Hierarchical Addressing: Route Aggregration

    • Efficient advertisement of routing information through ISP blocks and subnets with hierarchical addressing and aggregation
    • Route aggregation to advertisement from ISP to ISP and within Organizations reduces routing load and traffic.

    Hierarchical Addressing: More Specific Routes

    • More specific routes for organizations, given by Internet service providers (ISPs).
    • Allows ISP-level route advertisements
    • Examples are shown in diagrams

    IP Addressing: Last Word...

    • ICANN (Internet Corporation for Assigned Names and Numbers)
    • Allocates IP addresses, manages DNS, assigns domain names, and address resolution.

    DHCP Overview

    • DHCP dynamically assigns the IP address to a client on a network
    • Protocols and messages involved in the process
      • discover
      • offer
      • request
      • ACK.
    • Useful for mobile users and when it dynamically assigns the IP address based on the network usage.

    DHCP Client-Server Scenarios

    • arriving client needs the IP in a network
    • DHCP server gives an IP to the client.

    DHCP: More than IP Addresses

    • DHCP can return addresses of first-hop router, DNS server, and network mask to client.

    IP Addresses: How to Get One?

    • Hard-coded in a file by system administrator
    • DHCP(Dynamic Host Configuration Protocol)

    NAT (Network Address Translation)

    • Motivation: Local networks use just one IP address for outside world visibility.
    • Implementation: Router needs NAT translation table to remember source IP & port to NAT IP & port mapping for outgoing datagrams and the opposite for incoming ones.

    NAT Traversal Problem

    • Solutions: Static configuration to forward incoming connections through NAT.

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    Related Documents

    Chapter 4 Network Layer PDF

    Description

    Test your knowledge on the critical functions of the network layer, including forwarding, routing, and protocols. This quiz covers essential concepts that are foundational for understanding how data is transported across networks. Challenge your understanding of how routers manage IP datagrams and the different service models in the network layer.

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