Network Layer: Introduction and Services
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Questions and Answers

What is the primary responsibility of the network layer in the TCP/IP protocol suite?

  • Providing a connection-oriented service
  • Path determination between the source and destination
  • Host-to-host delivery of datagrams (correct)
  • Error-free transfer of data

    • What happens to a packet at the source host in the network layer?

  • It is decapsulated and delivered to the transport layer
  • It is encapsulated in a datagram and delivered to the data-link layer (correct)
  • It is stored temporarily until a connection is established
  • It is discarded if it is not properly formatted

    • What is required for successful communication between two devices at a communication layer?

  • The same protocol on each side of the connection (correct)
  • Different protocols on each side of the connection
  • A network layer that supports multiple protocols
  • A router with multiple data-link layers and physical layers

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

    <p>To deliver packets from one network to another</p> Signup and view all the answers

    At the destination host, what happens to a datagram in the network layer?

    <p>It is decapsulated, and the packet is extracted and delivered to the transport layer</p> Signup and view all the answers

    What is shown in Figure (1) of the network layer?

    <p>The communication between Alice and Bob</p> Signup and view all the answers

    What is the primary duty of the network layer?

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

    What happens to the packet header when a packet is fragmented?

    <p>It is copied to all fragments</p> Signup and view all the answers

    What is the responsibility of the routers in the path?

    <p>Forwarding packets</p> Signup and view all the answers

    What is the term for the process of delivering packets from the source to the destination without changing them?

    <p>Carrier service</p> Signup and view all the answers

    What is the purpose of the routing protocols?

    <p>Defining the best route</p> Signup and view all the answers

    What is the forwarding table used for?

    <p>Making forwarding decisions</p> Signup and view all the answers

    What is the result of the routing process?

    <p>Creation of the forwarding table</p> Signup and view all the answers

    What is the purpose of the error control mechanism?

    <p>Detecting corrupted, lost, or duplicate datagrams</p> Signup and view all the answers

    What is the key difference between unicast and multicast routing?

    <p>Number of attached networks</p> Signup and view all the answers

    What is the role of the network layer in packet delivery?

    <p>Carrying a payload from the source to the destination</p> Signup and view all the answers

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

    <p>Host-to-host delivery and routing of packets</p> Signup and view all the answers

    Why is error control not implemented in the network layer of the Internet?

    <p>Because it is inefficient due to packet fragmentation</p> Signup and view all the answers

    What is the role of ICMP in the Internet?

    <p>Providing an auxiliary protocol for error control</p> Signup and view all the answers

    What is the difference between a switch and a router?

    <p>A switch is a connecting device, while a router is a type of switch</p> Signup and view all the answers

    What is the primary advantage of packet switching over circuit switching?

    <p>It is more efficient in terms of resource utilization</p> Signup and view all the answers

    What is the primary difference between the datagram approach and the virtual circuit approach?

    <p>The datagram approach is connectionless, while the virtual circuit approach is connection-oriented</p> Signup and view all the answers

    What is the role of the flow label in a connection-oriented packet-switched network?

    <p>It defines the virtual path the packet should follow</p> Signup and view all the answers

    What is the primary reason for using packet switching in the Internet?

    <p>It is more efficient in terms of resource utilization</p> Signup and view all the answers

    What is the primary difference between the original design of the network layer and its recent development?

    <p>The original design was connectionless, while the recent development is connection-oriented</p> Signup and view all the answers

    What is the primary function of a router in a packet-switched network?

    <p>To route packets based on the destination address</p> Signup and view all the answers

    What is the purpose of the setup phase in a connection-oriented packet switched network?

    <p>To create table entries for the connection-oriented service</p> Signup and view all the answers

    What is the function of the acknowledgment packet?

    <p>To complete the entries in the switching tables</p> Signup and view all the answers

    What is latency in a network?

    <p>The total time taken for a complete message to arrive at the destination</p> Signup and view all the answers

    What is throughput in a network?

    <p>The actual measurement of how fast we can send data</p> Signup and view all the answers

    What is the unit of measurement for latency?

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

    What is the effect of high latency on a network?

    <p>It decreases the bandwidth of the network</p> Signup and view all the answers

    What is the difference between bandwidth and throughput?

    <p>Bandwidth is the potential measurement of a link, while throughput is the actual measurement of how fast we can send data</p> Signup and view all the answers

    What is the effect of packet loss on the Internet network layer?

    <p>The packet needs to be resent, which may create overflow and cause more packet loss</p> Signup and view all the answers

    What is the purpose of the request packet?

    <p>To request a virtual circuit from the source to the destination</p> Signup and view all the answers

    What is the term for network connections where small delays occur?

    <p>Low-Latency-Networks</p> Signup and view all the answers

    What is the purpose of subnetting?

    <p>To divide a large block into smaller ones</p> Signup and view all the answers

    What is the total number of addresses used by the protocol?

    <p>The address space</p> Signup and view all the answers

    What are the factors that affect throughput?

    <p>Available bandwidth, available signal-to-noise ratio, and hardware limitations</p> Signup and view all the answers

    What is the reason for the obsolescence of classful addressing?

    <p>Address depletion</p> Signup and view all the answers

    What is the purpose of supernetting?

    <p>To combine several class C blocks into a larger block</p> Signup and view all the answers

    What is the size of the IPv4 address?

    <p>32-bit</p> Signup and view all the answers

    What is the maximum number of devices that can be connected to the Internet using IPv4 addresses?

    <p>More than 4 billion</p> Signup and view all the answers

    What is the effect of congestion on the throughput?

    <p>It decreases the throughput</p> Signup and view all the answers

    What is the purpose of the input buffer in a router?

    <p>To store packets waiting for processing</p> Signup and view all the answers

    What is the prefix length in an IPv4 address?

    <p>Fixed and variable</p> Signup and view all the answers

    What is the main reason that classful addressing has become obsolete?

    <p>Address depletion</p> Signup and view all the answers

    What happens in subnetting?

    <p>A class A or class B block is divided into several subnets</p> Signup and view all the answers

    What is the advantage of classful addressing?

    <p>The prefix length is inherent in the address</p> Signup and view all the answers

    What is the purpose of supernetting?

    <p>To combine several blocks into a larger block</p> Signup and view all the answers

    What is the characteristic of the prefix length in classless addressing?

    <p>It is variable and ranges from 0 to 32</p> Signup and view all the answers

    What is the purpose of the slash notation in classless addressing?

    <p>To indicate the prefix length</p> Signup and view all the answers

    How do you find the first address in a block in classless addressing?

    <p>Keep the n leftmost bits and set the (32 - n) rightmost bits all to 0s</p> Signup and view all the answers

    What is the main difference between classful and classless addressing?

    <p>Classful addressing uses fixed-length blocks, while classless addressing uses variable-length blocks</p> Signup and view all the answers

    What is the result of dividing a range of addresses into several subranges and assigning each subrange to a subnetwork?

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

    What is the main concept behind classless addressing?

    <p>Using variable-length blocks to divide the address space</p> Signup and view all the answers

    What is the formula to find the prefix length for each subnetwork?

    <p>nsub = 32 - log2Nsub</p> Signup and view all the answers

    What is the purpose of the slash notation?

    <p>To separate the prefix and suffix of an address</p> Signup and view all the answers

    What is the relationship between the size of a network and its prefix length?

    <p>A small prefix means a larger network</p> Signup and view all the answers

    What is the advantage of classless addressing?

    <p>It is compatible with classful addressing</p> Signup and view all the answers

    What is the formula to find the number of addresses in a block?

    <p>N = 232 - n</p> Signup and view all the answers

    What is the first step in designing subnets?

    <p>Assign addresses to larger subnetworks</p> Signup and view all the answers

    What is the purpose of subnetting?

    <p>To divide a network into smaller subnetworks</p> Signup and view all the answers

    What is the relationship between the number of addresses in each subnetwork and the prefix length?

    <p>The number of addresses is inversely proportional to the prefix length</p> Signup and view all the answers

    What is the benefit of using classless addressing?

    <p>It provides more flexibility in assigning addresses</p> Signup and view all the answers

    What is the primary function of DHCP in a network?

    <p>To dynamically assign IP addresses and other network configuration parameters</p> Signup and view all the answers

    What is the device that allocates and manages IP addresses and other configuration parameters in a network?

    <p>DHCP Server</p> Signup and view all the answers

    What is the term for the temporary assignment of IP addresses and other configuration parameters to DHCP clients?

    <p>IP Address Lease</p> Signup and view all the answers

    What is the purpose of the DHCP Discover message?

    <p>To discover available DHCP servers on a network</p> Signup and view all the answers

    What is the technology that allows a site to use private addresses for internal communication and global Internet addresses for communication with the rest of the world?

    <p>Network Address Translation (NAT)</p> Signup and view all the answers

    What type of NAT maps a private IP address to a specific public IP address?

    <p>Static NAT</p> Signup and view all the answers

    What is the term for delivering packets from the source to the destination without changing them?

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

    When is a DHCP client required to renew its lease?

    <p>When the lease time expires</p> Signup and view all the answers

    What is the purpose of the DHCP Request message?

    <p>To respond to a DHCP Offer message</p> Signup and view all the answers

    What is the term for the process of assigning IP addresses and other network configuration parameters to devices on a network?

    <p>Dynamic Host Configuration</p> Signup and view all the answers

    What happens to a packet at the destination host in the network layer?

    <p>The datagram is decapsulated, and the packet is extracted and delivered to the corresponding transport layer</p> Signup and view all the answers

    What is the key point to remember when communicating at each communication layer?

    <p>The same protocol must be used at each side of a connection</p> Signup and view all the answers

    How many data-link layers and physical layers does a router in the path normally have?

    <p>Two data-link layers and two physical layers</p> Signup and view all the answers

    What is the role of the network layer at the source host?

    <p>To accept a packet from the transport layer, encapsulate it in a datagram, and deliver it to the data-link layer</p> Signup and view all the answers

    What happens to a packet at the source host after it is encapsulated in a datagram?

    <p>It is delivered to the data-link layer</p> Signup and view all the answers

    What is the purpose of the network layer in the TCP/IP protocol suite?

    <p>To provide services to the transport layer and receive services from the data-link layer</p> Signup and view all the answers

    Why was error control not implemented in the network layer of the Internet?

    <p>Because it was inefficient due to packet fragmentation</p> Signup and view all the answers

    What is the primary function of a router in a packet-switched network?

    <p>To forward packets to their destination</p> Signup and view all the answers

    What is the primary function of the network layer in packet delivery?

    <p>To route packets from the source to the destination</p> Signup and view all the answers

    What is the main difference between circuit switching and packet switching?

    <p>Packet switching divides the message into packets, while circuit switching establishes a physical circuit</p> Signup and view all the answers

    What is the key difference between unicast and multicast routing?

    <p>The number of destinations</p> Signup and view all the answers

    What is the role of the forwarding table in a router?

    <p>To make decisions about packet forwarding</p> Signup and view all the answers

    What is the function of the flow label in a connection-oriented packet-switched network?

    <p>To define the virtual path for the packets</p> Signup and view all the answers

    What happens to the packet header when a packet is fragmented?

    <p>It is copied to all fragments</p> Signup and view all the answers

    What is the main difference between the datagram approach and the virtual circuit approach?

    <p>Datagram approach is connectionless, while virtual circuit approach is connection-oriented</p> Signup and view all the answers

    What is the purpose of routing protocols?

    <p>To define the best route to the destination</p> Signup and view all the answers

    What is the purpose of ICMP in the Internet?

    <p>To provide an auxiliary protocol for error control</p> Signup and view all the answers

    Why is packet switching preferred over circuit switching in the Internet?

    <p>Because packet switching is more flexible and adaptable to network changes</p> Signup and view all the answers

    What is the responsibility of the routers in the path?

    <p>To forward packets to the next hop</p> Signup and view all the answers

    What is the purpose of error control mechanisms?

    <p>To detect corrupted, lost, or duplicate packets</p> Signup and view all the answers

    What happens to the packets in a packet-switched network?

    <p>They are assembled at the destination</p> Signup and view all the answers

    What is the primary responsibility of the network layer in the Internet?

    <p>To route packets from the source to the destination</p> Signup and view all the answers

    What is the role of the network layer in packet delivery?

    <p>To carry the payload from the source to the destination</p> Signup and view all the answers

    What is the term for the process of forwarding packets to their destination?

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

    What is the term for delivering packets from the source to the destination without changing them?

    <p>Carrier service</p> Signup and view all the answers

    What is the primary function of the network layer?

    <p>To carry the payload from the source to the destination</p> Signup and view all the answers

    What is the purpose of the setup phase in a connection-oriented packet-switched network?

    <p>Creating table entries for the connection-oriented service</p> Signup and view all the answers

    What is latency in a network?

    <p>The total time taken for a complete message to arrive at the destination</p> Signup and view all the answers

    What is the difference between bandwidth and throughput?

    <p>Bandwidth is the potential measurement of a link, while throughput is the actual measurement of how fast data can be sent</p> Signup and view all the answers

    What is the effect of high latency on a network?

    <p>It creates bottlenecks in the network and decreases the bandwidth</p> Signup and view all the answers

    What is the purpose of the acknowledgment packet?

    <p>To complete the entries in the switching tables</p> Signup and view all the answers

    What is the unit of measurement for latency?

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

    What is the term for network connections where small delays occur?

    <p>Low-Latency-Networks</p> Signup and view all the answers

    What is the purpose of the request packet?

    <p>To request a connection from the source to the destination</p> Signup and view all the answers

    What is the formula for latency?

    <p>Propagation Time + Transmission Time + Queuing Time + Processing Delay</p> Signup and view all the answers

    What is throughput in a network?

    <p>The number of messages successfully transmitted per unit time</p> Signup and view all the answers

    What is the maximum achievable throughput that can be affected by numerous protocol expenses?

    <p>The actual throughput</p> Signup and view all the answers

    What happens to a packet when a router receives it while processing another packet?

    <p>The packet is stored in the input buffer</p> Signup and view all the answers

    What is the total number of addresses used by the IPv4 protocol?

    <p>2^32</p> Signup and view all the answers

    What is the main reason that classful addressing has become obsolete?

    <p>Address depletion</p> Signup and view all the answers

    What is the purpose of subnetting in IPv4?

    <p>To divide a large block into smaller ones</p> Signup and view all the answers

    What happens to the packet that needs to be dropped when the input buffer is full?

    <p>It is discarded</p> Signup and view all the answers

    What is the effect of packet loss on the Internet network layer?

    <p>The packet is resent</p> Signup and view all the answers

    What is the size of the IPv4 address?

    <p>32 bits</p> Signup and view all the answers

    What is the advantage of classful addressing?

    <p>Given an address, we can easily find the class of the address</p> Signup and view all the answers

    What is the effect of congestion on the throughput?

    <p>It decreases the throughput</p> Signup and view all the answers

    What is the main reason classful addressing has become obsolete?

    <p>Address depletion</p> Signup and view all the answers

    What is the purpose of subnetting?

    <p>To divide a large block into smaller ones</p> Signup and view all the answers

    What is the advantage of classful addressing?

    <p>Easy to extract the prefix and suffix</p> Signup and view all the answers

    In classless addressing, what determines the block (network) and the node (device)?

    <p>The prefix defines the block, and the suffix defines the node</p> Signup and view all the answers

    What is the notation informally referred to as slash notation?

    <p>CIDR strategy</p> Signup and view all the answers

    What can be found using the prefix length, n?

    <p>The number of addresses, the first address, and the last address</p> Signup and view all the answers

    Why did class B addresses remain unused?

    <p>They were too small for most companies</p> Signup and view all the answers

    What was the problem with Class C addresses?

    <p>The number of addresses that can be used in each network was too small</p> Signup and view all the answers

    What is the idea behind supernetting?

    <p>To combine several class C blocks into a larger block</p> Signup and view all the answers

    In classless addressing, what is the relationship between the size of the network and the length of the prefix?

    <p>A small prefix means a larger network</p> Signup and view all the answers

    What is the main function of the DHCP server?

    <p>To manage and allocate IP addresses and other network configuration parameters</p> Signup and view all the answers

    What happens when a DHCP client's lease expires?

    <p>The IP address is released and returned to the DHCP pool for reuse</p> Signup and view all the answers

    What is the purpose of Network Address Translation (NAT)?

    <p>To map private IP addresses to public IP addresses</p> Signup and view all the answers

    What is the term for the process of delivering packets from the source to the destination without changing them?

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

    What is the difference between static NAT and dynamic NAT?

    <p>Static NAT maps a private IP address to a specific public IP address, while dynamic NAT maps private IP addresses to public IP addresses from a pool</p> Signup and view all the answers

    What is the purpose of the DHCP Discover message?

    <p>To discover available DHCP servers on the network</p> Signup and view all the answers

    What is the term for the temporary assignment of IP addresses and other configuration parameters to DHCP clients?

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

    What is the purpose of the DHCP Offer message?

    <p>To offer an IP address and configuration parameters to the DHCP client</p> Signup and view all the answers

    What is the purpose of the DHCP Acknowledgment message?

    <p>To confirm the assignment of the IP address and provide the client with the configuration parameters</p> Signup and view all the answers

    What happens when a DHCP client needs to renew its lease?

    <p>The client sends a DHCP Request message to the DHCP server</p> Signup and view all the answers

    What is the total number of addresses granted to an organization assumed to be?

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

    What is the formula to find the prefix length for each subnetwork?

    <p>nsub = 32 - log2Nsub</p> Signup and view all the answers

    What is the main difference between classless addressing and classful addressing?

    <p>Classful addressing uses fixed-length blocks, while classless addressing uses variable-length blocks</p> Signup and view all the answers

    How do you find the number of addresses in a block?

    <p>N = 232 - n</p> Signup and view all the answers

    What is the purpose of subnetting?

    <p>To divide a range of addresses into several subranges</p> Signup and view all the answers

    What is the notation used to represent the prefix length in an address?

    <p>Slash notation</p> Signup and view all the answers

    How do you find the first address in a block?

    <p>Keep the n leftmost bits and set the (32 - n) rightmost bits all to 0s</p> Signup and view all the answers

    What is the size of the network inversely proportional to?

    <p>The prefix length</p> Signup and view all the answers

    What is the advantage of dividing a subnetwork into several sub-subnetworks?

    <p>It provides more flexibility in assigning addresses</p> Signup and view all the answers

    What is the result of a subnetwork being divided into several sub-subnetworks?

    <p>An increase in the number of subnetworks</p> Signup and view all the answers

    Study Notes

    Network Layer Services

    • The network layer is responsible for host-to-host delivery of datagrams.
    • It provides services to the transport layer and receives services from the data-link layer.
    • The network layer is involved at the source host, destination host, and all routers in the path.

    Packetizing

    • The network layer's first duty is packetizing, which is encapsulating the payload (data received from the upper layer) in a network-layer packet at the source and decapsulating the payload from the network-layer packet at the destination.
    • The network layer is responsible for carrying a payload from the source to the destination without changing it or using it.

    Routing

    • The network layer is responsible for routing the packet from its source to the destination.
    • The network layer needs to have some specific strategies for defining the best route.
    • Routing protocols are used to help the routers coordinate their knowledge about the neighborhood and to come up with consistent tables to be used when a packet arrives.

    Forwarding

    • Forwarding is the action applied by each router when a packet arrives at one of its interfaces.
    • The decision-making table used by a router is called the forwarding table or routing table.
    • When a router receives a packet from one of its attached networks, it needs to forward the packet to another attached network (in unicast routing) or to some attached networks (in multicast routing).

    Error Control

    • Error control means including a mechanism for detecting corrupted, lost, or duplicate datagrams.
    • Error control also includes a mechanism for correcting errors after they have been detected.
    • The Internet does not directly provide error control at the network layer, but uses an auxiliary protocol, ICMP, which provides some kind of error control.

    Switching

    • Switching is the process of selecting one of the output ports through which the packet needs to be sent out.
    • The two types of switching are:
      • Circuit switching: a physical circuit (or channel) is established between the source and destination of the message before the delivery of the message.
      • Packet switching: the message is divided into manageable packets at the source before being transmitted, and the packets are assembled at the destination.

    Packet Switching at Network Layer

    • The network layer is designed as a packet-switched network.
    • The packet-switched network layer of the Internet was originally designed as a Connectionless service, but recently there is a tendency to change this to a Connection-oriented service.
    • The two approaches to packet switching are:
      • Datagram approach: each packet is routed independently, and the packets in a message may or may not travel the same path to their destination.
      • Virtual-circuit approach: a virtual connection is set up to define the path for the datagrams, and the datagrams follow the same path.

    Network Layer Performance

    • The performance of a network pertains to the measure of service quality of a network as perceived by the user.
    • The performance of a network can be measured in terms of:
      • Routing efficiency: latency (delay) and throughput
      • Packet loss: the number of packets lost during transmission

    Latency

    • Latency is defined as the total time taken for a complete message to arrive at the destination, starting with the time when the first bit of the message is sent out from the source and ending with the time when the last bit of the message is delivered at the destination.
    • Latency is measured in milliseconds (ms).

    Throughput

    • Throughput is the number of messages successfully transmitted per unit time.
    • Throughput is controlled by available bandwidth, the available signal-to-noise ratio, and hardware limitations.
    • Throughput is measured in terms of bits per second (bps), bytes per second (Bps), kilobytes per second (KBps), megabytes per second (MBps), and gigabytes per second (Gbps).

    Packet Loss

    • Packet loss is the number of packets lost during transmission.
    • Packet loss can be caused by congestion in the network, and can lead to overflow and cause more packet loss.

    IPv4 Address

    • An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet.
    • IPv4 addresses are hierarchical, with a prefix that defines the network and a suffix that defines the node (connection of a device to the Internet).
    • The address space of IPv4 is 2^32, or 4,294,967,296.

    Classful Addressing

    • Classful addressing is a system of addressing that divides the address space into five classes (A, B, C, D, and E).
    • Each class has a fixed prefix length, which determines the number of nodes that can be connected to the Internet.
    • Classful addressing has become obsolete due to address depletion.

    Subnetting and Supernetting

    • Subnetting is a technique of dividing a class A or class B block into several subnets.
    • Supernetting is a technique of combining several class C blocks into a larger block.
    • Both subnetting and supernetting were devised to conserve addresses and make routing more efficient.

    Classless Addressing

    • Classless addressing is a system of addressing that uses variable-length blocks.
    • In classless addressing, the whole address space is divided into variable-length blocks.
    • The prefix length in classless addressing is variable, and can range from 0 to 32.
    • Classless addressing is more flexible and efficient than classful addressing.### Classless Addressing
    • An address in class A, B, C can be thought of as a classless address with a prefix length of 8, 16, and 24 respectively.
    • Classful addressing is a special case of classless addressing.

    Prefix Length and Slash Notation

    • The prefix length, n, is added to the address, separated by a slash (/).
    • This notation is informally referred to as slash notation and formally as Classless Interdomain Routing (CIDR).

    Extracting Information from an Address

    • Three pieces of information can be extracted from an address:
      • The number of addresses in the block: N = 2^(32-n)
      • The first address in the block: keep the n leftmost bits and set the (32 - n) rightmost bits to 0s
      • The last address in the block: keep the n leftmost bits and set the (32 - n) rightmost bits to 1s

    Subnetting

    • An organization can divide a range of addresses into several subranges and assign each subrange to a subnetwork (subnet).
    • A subnet can be divided into several sub-subnets, and so on.
    • Designing subnets requires careful planning to guarantee proper operation.

    Designing Subnets

    • The number of addresses in each subnetwork should be a power of 2.
    • The prefix length for each subnetwork should be found using the formula: nsub = 32 - log2Nsub.
    • The starting address in each subnetwork should be divisible by the number of addresses in that subnetwork.

    DHCP (Dynamic Host Configuration Protocol)

    • DHCP is a network management protocol used to dynamically assign IP addresses and other network configuration parameters to devices on a network.
    • DHCP operates on the client-server model, where a DHCP server manages and allocates IP addresses to DHCP clients.

    DHCP Server and Client

    • The DHCP server is responsible for allocating and managing IP addresses and other configuration parameters.
    • The DHCP client requests and obtains network configuration information from a DHCP server.

    DHCP Leases

    • DHCP leases are temporary assignments of IP addresses and other configuration parameters to DHCP clients.
    • Leases have a duration, known as the lease time, after which the client must renew its lease.

    DHCP Messages

    • DHCP Discover: The DHCP client broadcasts a message to discover available DHCP servers on the network.
    • DHCP Offer: DHCP servers respond to DHCP Discover messages with DHCP Offer messages.
    • DHCP Request: The DHCP client selects an offered IP address and sends a DHCP Request message to the chosen DHCP server.
    • DHCP Acknowledgment: The DHCP server sends a DHCP Acknowledgment message to confirm the assignment of the IP address and provide the client with the configuration parameters.

    NAT (Network Address Translation)

    • NAT is a technology that provides the mapping between private and universal addresses and supports virtual private networks.
    • NAT types: Static NAT, Dynamic NAT, and NAT Overload (PAT - Port Address Translation).

    Forwarding of IP Packets

    • Forwarding means to deliver the packet to the next hop, which can be the final destination or an intermediate connecting device.
    • Forwarding can be based on the destination address of the IP datagram or the label attached to an IP datagram.
    • A forwarding table is used to find the next hop to deliver the packet to.

    Network Layer Services

    • The network layer is responsible for host-to-host delivery of datagrams.
    • It provides services to the transport layer and receives services from the data-link layer.
    • The network layer is involved at the source host, destination host, and all routers in the path.

    Packetizing

    • The network layer's first duty is packetizing, which is encapsulating the payload (data received from the upper layer) in a network-layer packet at the source and decapsulating the payload from the network-layer packet at the destination.
    • The network layer is responsible for carrying a payload from the source to the destination without changing it or using it.

    Routing

    • The network layer is responsible for routing the packet from its source to the destination.
    • The network layer needs to have some specific strategies for defining the best route.
    • Routing protocols are used to help the routers coordinate their knowledge about the neighborhood and to come up with consistent tables to be used when a packet arrives.

    Forwarding

    • Forwarding is the action applied by each router when a packet arrives at one of its interfaces.
    • The decision-making table used by a router is called the forwarding table or routing table.
    • When a router receives a packet from one of its attached networks, it needs to forward the packet to another attached network (in unicast routing) or to some attached networks (in multicast routing).

    Error Control

    • Error control means including a mechanism for detecting corrupted, lost, or duplicate datagrams.
    • Error control also includes a mechanism for correcting errors after they have been detected.
    • The Internet does not directly provide error control at the network layer, but uses an auxiliary protocol, ICMP, which provides some kind of error control.

    Switching

    • Switching is the process of selecting one of the output ports through which the packet needs to be sent out.
    • The two types of switching are:
      • Circuit switching: a physical circuit (or channel) is established between the source and destination of the message before the delivery of the message.
      • Packet switching: the message is divided into manageable packets at the source before being transmitted, and the packets are assembled at the destination.

    Packet Switching at Network Layer

    • The network layer is designed as a packet-switched network.
    • The packet-switched network layer of the Internet was originally designed as a Connectionless service, but recently there is a tendency to change this to a Connection-oriented service.
    • The two approaches to packet switching are:
      • Datagram approach: each packet is routed independently, and the packets in a message may or may not travel the same path to their destination.
      • Virtual-circuit approach: a virtual connection is set up to define the path for the datagrams, and the datagrams follow the same path.

    Network Layer Performance

    • The performance of a network pertains to the measure of service quality of a network as perceived by the user.
    • The performance of a network can be measured in terms of:
      • Routing efficiency: latency (delay) and throughput
      • Packet loss: the number of packets lost during transmission

    Latency

    • Latency is defined as the total time taken for a complete message to arrive at the destination, starting with the time when the first bit of the message is sent out from the source and ending with the time when the last bit of the message is delivered at the destination.
    • Latency is measured in milliseconds (ms).

    Throughput

    • Throughput is the number of messages successfully transmitted per unit time.
    • Throughput is controlled by available bandwidth, the available signal-to-noise ratio, and hardware limitations.
    • Throughput is measured in terms of bits per second (bps), bytes per second (Bps), kilobytes per second (KBps), megabytes per second (MBps), and gigabytes per second (Gbps).

    Packet Loss

    • Packet loss is the number of packets lost during transmission.
    • Packet loss can be caused by congestion in the network, and can lead to overflow and cause more packet loss.

    IPv4 Address

    • An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet.
    • IPv4 addresses are hierarchical, with a prefix that defines the network and a suffix that defines the node (connection of a device to the Internet).
    • The address space of IPv4 is 2^32, or 4,294,967,296.

    Classful Addressing

    • Classful addressing is a system of addressing that divides the address space into five classes (A, B, C, D, and E).
    • Each class has a fixed prefix length, which determines the number of nodes that can be connected to the Internet.
    • Classful addressing has become obsolete due to address depletion.

    Subnetting and Supernetting

    • Subnetting is a technique of dividing a class A or class B block into several subnets.
    • Supernetting is a technique of combining several class C blocks into a larger block.
    • Both subnetting and supernetting were devised to conserve addresses and make routing more efficient.

    Classless Addressing

    • Classless addressing is a system of addressing that uses variable-length blocks.
    • In classless addressing, the whole address space is divided into variable-length blocks.
    • The prefix length in classless addressing is variable, and can range from 0 to 32.
    • Classless addressing is more flexible and efficient than classful addressing.### Classless Addressing
    • An address in class A, B, C can be thought of as a classless address with a prefix length of 8, 16, and 24 respectively.
    • Classful addressing is a special case of classless addressing.

    Prefix Length and Slash Notation

    • The prefix length, n, is added to the address, separated by a slash (/).
    • This notation is informally referred to as slash notation and formally as Classless Interdomain Routing (CIDR).

    Extracting Information from an Address

    • Three pieces of information can be extracted from an address:
      • The number of addresses in the block: N = 2^(32-n)
      • The first address in the block: keep the n leftmost bits and set the (32 - n) rightmost bits to 0s
      • The last address in the block: keep the n leftmost bits and set the (32 - n) rightmost bits to 1s

    Subnetting

    • An organization can divide a range of addresses into several subranges and assign each subrange to a subnetwork (subnet).
    • A subnet can be divided into several sub-subnets, and so on.
    • Designing subnets requires careful planning to guarantee proper operation.

    Designing Subnets

    • The number of addresses in each subnetwork should be a power of 2.
    • The prefix length for each subnetwork should be found using the formula: nsub = 32 - log2Nsub.
    • The starting address in each subnetwork should be divisible by the number of addresses in that subnetwork.

    DHCP (Dynamic Host Configuration Protocol)

    • DHCP is a network management protocol used to dynamically assign IP addresses and other network configuration parameters to devices on a network.
    • DHCP operates on the client-server model, where a DHCP server manages and allocates IP addresses to DHCP clients.

    DHCP Server and Client

    • The DHCP server is responsible for allocating and managing IP addresses and other configuration parameters.
    • The DHCP client requests and obtains network configuration information from a DHCP server.

    DHCP Leases

    • DHCP leases are temporary assignments of IP addresses and other configuration parameters to DHCP clients.
    • Leases have a duration, known as the lease time, after which the client must renew its lease.

    DHCP Messages

    • DHCP Discover: The DHCP client broadcasts a message to discover available DHCP servers on the network.
    • DHCP Offer: DHCP servers respond to DHCP Discover messages with DHCP Offer messages.
    • DHCP Request: The DHCP client selects an offered IP address and sends a DHCP Request message to the chosen DHCP server.
    • DHCP Acknowledgment: The DHCP server sends a DHCP Acknowledgment message to confirm the assignment of the IP address and provide the client with the configuration parameters.

    NAT (Network Address Translation)

    • NAT is a technology that provides the mapping between private and universal addresses and supports virtual private networks.
    • NAT types: Static NAT, Dynamic NAT, and NAT Overload (PAT - Port Address Translation).

    Forwarding of IP Packets

    • Forwarding means to deliver the packet to the next hop, which can be the final destination or an intermediate connecting device.
    • Forwarding can be based on the destination address of the IP datagram or the label attached to an IP datagram.
    • A forwarding table is used to find the next hop to deliver the packet to.

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    Description

    This quiz covers the basics of the network layer in the TCP/IP protocol suite, including its services and communication process. It explains how the network layer enables host-to-host delivery of datagrams and interacts with the transport and data-link layers.

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