• Unit 5: The Network Layer

    In this unit, we will learn how packets (groupings of data) travel on a network and how each machine can be addressed uniquely so that data transport between two nodes is reliable. We will learn that networks can run out of space, meaning that unique addresses for different machines are no longer available. In these situations, computer scientists must manage IP addressing using CIDR and subnetting – techniques we will learn about in this unit.

    The network layer is responsible for the delivery of packets from any source to any destination through intermediate routers. Follow the links to explore in detail the IPv4, IPv6, RIP, OSPF, and BGP protocols used in today's Internet.

    Completing this unit should take you approximately 11 hours.

    • Upon successful completion of this unit, you will be able to:

      • explain the correct network layer protocol to perform packet forwarding using both IPv4 and IPv6;
      • configure and illustrate IP addressing and explain its purpose, on both IPv4 and IPv6 networks;
      • compare and contrast Classless Interdomain Routing (CIDR) with subnetting activities within the network layer;
      • use protocols like Dynamic Host Configuration Protocol (DHCP), Address Resolution Protocol (ARP), and Network Address Translation (NAT) to manage IP address assignment, re-assignment, and resolution;
      • illustrate the use of Interior Routing Protocols based on shortest path, distance vector, and link state routing models;
      • compare and contrast interior routing protocols like Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) with exterior routing protocols like Border Gateway Protocol (BGP);
      • use multicasting principles including addressing schemes and associated protocols;
      • use quality of service (QoS) principles and associated protocols like Multiprotocol Label Switching (MPLS); and
      • use protocols like Internet Control Message Protocol (ICMP) to configure and troubleshoot a network in both IPv4 and IPv6.

    • 5.1: Principles

      • Principles Page

        The network layer includes the datagram and virtual circuit modes, the separation between the data plane and the control plane, and the algorithms used by routing protocols.

        As you read this section, it is important to understand the purpose of the router and the use of the packet in enabling you to send data and receive the response. How does the packet interact with the router?

      • 5.1.1: Organization of the Network Layer

        • Organisation of the Network Layer Page

          What are the two internal organizations used in the network layer? When are each used? What is a datagram? Explore this section of your textbook to see how a datagram is used at the network level. Compare and contrast the datagram organization with the virtual circuit discussed in this section.

          The concept of hop-by-hop forwarding is this section. What does this concept have to do with the routing table? What is the difference between the data and control planes?

      • 5.1.2: The Control Plane

        • The Control Plane Page

          In this section, the textbook explains how the control plane maintains the routing table. The three techniques to accomplish this are static routing, distance vector routing, and link state routing. As you explore the next three subunits describing each one in detail, note the advantages and disadvantages of each technique. How does each method deal with link and router failures?

        • 5.1.2.1: Static Routing

          • Static Routing Page

            As you read this section, consider the following questions: What is static routing? What are its advantages and disadvantages?

        • 5.1.2.2: Distance Vector Routing

          • Distance Vector Routing Page

            As you read this section, consider the following questions: What is distance vector routing? What are its advantages and disadvantages?

        • 5.1.2.3: Link State Routing

          • Link State Routing Page

            As you read this section, consider the following questions: What is link state routing? What are its advantages and disadvantages? How does link state routing handle link and routing failures?

          • Bellman-Ford Algorithm Page

            Read this article for more details about the Bellman-Ford routing algorithm. This routing protocol is used in RIP, OSPF, and BGP.

          • Dijkstra's Algorithm Page

            Read this article for more details about the Dijkstra routing algorithm. What is the Dijkstra Algorithm? How is the Dijkstra Algorithm used in link state routing? Like the Bellman-Ford algorithm, this routing protocol is used in RIP, OSPF, and BGP.

    • 5.2: Internet Protocol

      • Internet Protocol Page

        In this section we will explore the Internet Protocol (IP) to discover how IP enables the applications running above the transport layer (UDP/TCP) to utilize any of the different datalink layers available.

      • 5.2.1: IP version 4 (IPv4)

        • IP version 4 Page

          This section starts with a discussion of IP version 4 before exploring network addressing in more detail. As you read, consider the following questions: What are two of the problems with IP version 4 that led to the development of the Classless Interdomain Routing (CIDR) architecture? How does CIDR improve the scalability of the IP routing system?

        • Subnetting and Supernetting Book

          Read these two files for a deeper and more detailed understanding of the need and use of subnetting and supernetting. Make sure that you understand the exact subnet where an address/mask combination belongs to. Once you determine the exact subnet, make sure that you can name the first and last hosts on that subnet, as well as the network name and broadcast address. Very important principles that need to be mastered.

      • 5.2.2: Internet Control Message Protocol (ICMP) Version 4

        • ICMP version 4 Page

          Sometimes a router or the destination host has to inform the sender of the packet of a problem that occurred while processing that packet. In the TCP/IP protocol suite, this reporting is done by the Internet Control Message Protocol (ICMP). How are these messages generated by the ICMP?

      • 5.2.3: IP version 6 (IPv6)

        • IP version 6 Page

          Read this section. As the popularity of the Internet grew exponentially, it became necessary for an expanded addressing architecture, IP version 6 (IPv6). This section discusses how IPv6 has resolved a number of routing issues while becoming the new standard.

      • 5.2.4: ICMP Version 6 (ICMPv6)

        • ICMP version 6 Page

          ICMPv6 is the companion protocol for IPv6, just as ICMPv4 is the companion protocol for IPv4. ICMPv6 is used by routers and hosts to report problems when processing IPv6 packets. In addition, ICMPv6 is used when auto-configuring addresses. This section discusses messaging for IPv6.

      • 5.2.5: Middleboxes

        • Middleboxes Page

          As you read this section, consider the following questions: What is a Middlebox? Why do we need them?

      • 5.2.6: Network Address Translation (NAT)

        • NAT Page

          Large corporations and government agencies prefer their networks to be private (that is, not seen on the Internet). In this section, explore the concept of private networks to learn how their need to communicate with the outside world and with specific machines under certain conditions has resulted in NAT; the mechanism that allows private networks to communicate openly with the outside world. How does NAT work?

    • 5.3: Routing in IP Networks

      • Routing in IP Networks Page

        Read this section. Routing protocols will be discussed in terms of two classifications: intra domain and interdomain. What are the differences between these classifications?

      • 5.3.1: Intradomain Routing

        • 5.3.1.1: Routing Information Protocol (RIP)

          • RIP Page

            As you read this section, consider the following questions: What is RIP? What are the features of the RIP protocol? How does RIP meet the objectives of intra domain routing? What are its weaknesses?

        • 5.3.1.2: Open Shortest Path First (OSPF)

          • OSPF Page

            As you read this section, consider the following questions: What is OSPF? What are the features of the OSPF protocol? How does OSPF meet the objectives of intra domain routing? What are its weaknesses? How is OSPF different from RIP?

      • 5.3.2: Interdomain Routing

        • Interdomain Routing Page

          As you read this section, consider the following questions: What are the objectives of interdomain routing? What is the difference between transit and stub domains? What are some of the relationships you can expect to find in an interdomain routing policy?

          Describe the BGP. How does BGP differ from the intra domain protocols RIP and OSPF that you've studied? What messages might the BGP generate? What is router convergence? Why is router convergence necessary? How is router convergence handled by the BGP?

        • Multicasting Page

          Read this article about Multicasting. Make sure you fully understand the addressing scheme used for IP multicasting as well as the IGMP protocol used to control the traffic. Of particular importance is also the use of the Reverse Path Forwarding technique to avoid multiple copies of the same packet from being endlessly forwarded in the network.

        • Quality of Service Page

          Read this article about Quality of Service. Pay special attention to the ToS field, DiffServe, RSVP and MPLS.

    • 5.4: Practice Exercises

      • Exercises Page

        These exercises expand the key principles in this chapter. If you are a computer professional, you will enjoy the challenges and higher-level discussions in this section. If you are a novice, explore the presentations and spend more time on the topics that are meaningful to you.

      • The Network Simulator: ns-2 Page

        This is a software tool that helps you perform networking experiments on your computer. Download and try it with a few simple examples, such as exercise 5 (page 196) and 6 (page 197) in the textbook.

      • Network Device Scanning Page

        Follow the steps detailed in this document. You will learn how to scan for network devices in your local area network using a mobile device, in this case, the "LAN Scan HD" app.

    • Unit 5 Assessment

      • Unit 5 Assessment Quiz
        Receive a grade

        Take this assessment to see how well you understood this unit.

        • This assessment does not count towards your grade. It is just for practice!
        • You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
        • You can take this assessment as many times as you want, whenever you want.