Chapter 1 Understanding and Configuring IP
Like any communication system, computer networks rely on a set of standards that allow communicators to send, receive, and interpret messages. For the Internet, Windows networks, and virtually all other computer networks, that underlying set of standards is the suite of protocols known collectively as Transmission Control Protocol/Internet Protocol (TCP/IP), the core of which is IP.
Lesson 1: Understanding and Configuring Network Connections
Network connections in Windows are software interfaces that use TCP/IP and associated services to communicate over a network. This lesson helps you understand the concepts and features of TCP/IP, how you can configure Windows 11 network connections, and how to troubleshoot network connections by using basic TCP/IP utilities.
What Are Network Layers?
Network layers are conceptual steps in network communication that are performed by standards based programs called protocols. As an analogy, consider an assembly line. If a factory uses an assembly line to create a product that is assembled, coated, packaged, boxed, and labeled, for example, you could view these five sequential functions as vertically stacked layers in the production process. Following this analogy, the protocols in the assembly line are the specific machines or procedures used to carry out the function of each layer.
Although each protocol is designed to accept a specific input and generate a specific output, you could replace any protocol within the system as long as it remained compatible with the neighboring machines on the assembly line.
In a way, network communications really do resemble the creation of packaged products on an assembly line because computers communicate with one another by creating and sending encapsulated (wrapped) packages called packets. Unlike assembly-line production, however, communication between computers is bidirectional. This means that the networking layers taken together describe a way both to construct and deconstruct packets. Each layer, and each specific protocol, must be able to perform its function in both directions.
Exploring the Layers of the TCP/IP Networking Model
The idea of a layered networking model allows for the possibility that individual protocols at any layer can be replaced as long as the replacement protocols work seamlessly with the protocols at neighboring layers. Such a change has in fact recently happened with TCP/IP in Windows networks. Windows Server 2008 and Windows Vista have introduced a new implementation of the TCP/IP protocol stack known as the Next Generation TCP/IP stack. New protocols have been added to the stack, but this upgraded version of TCP/IP is still based on the same four-layer model.
NOTE:- TCP/IP layer numbers Although you will sometimes see the layers of the TCP/IP model assigned their own numbers independent of the OSI model, this book’s terminology reflects the layer number usage that is far more current.
Layer 2
Layer 2, also called the Network Interface Layer or Data Link Layer, is the step in the communication process that describes a specific set of standards for network adapters, hardware addresses (such as MAC addresses) assigned to those adapters, cabling type, hubs, switches, associated physical standards, and associated messaging protocols. The function of this layer is to deliver messages from one device to the next, and its protocols allow communications to occur between computers separated only by hubs, switches, and cabling. Examples of standards defined at the Network Interface Layer include Ethernet and Token Ring.
Layer 3
Also called the Network Layer or Internet Layer, Layer 3 is the step in the communication process during which a source and destination software address is added to the packet and during which the packet is routed to the remote network destination beyond the “earshot” of a physical signal. The main protocol that operates at Layer 3 is IP, and the device that operates at this layer is a router. Routers stop physical propagations (broadcasts) of messages on a network, read the software address assigned in Layer 3 of a packet, and then forward the message along an appropriate pathway toward its destination.
Layer 3 is where the main changes have appeared in Microsoft’s new implementation of TCP/ IP. Traditionally, IPv4 is the only protocol to appear at this layer. In the Next Generation TCP/ IP stack, however, the IPv4 and IPv6 protocols now co-occupy Layer 3.
■ IPv4 IPv4, or simply IP, is responsible for addressing and routing packets between hosts that might be dozens of network segments away. IPv4 relies on 32-bit addresses, and because of this relatively small address space, addresses are rapidly becoming depleted in IPv4 networks.
■ IPv6 IPv6 uses 128-bit addresses instead of the 32-bit addresses used with IPv4, and, as a result, it can define many more addresses. Because few Internet routers are IPv6 compatible, IPv6 today is used over the Internet with the help of tunneling protocols. However, IPv6 is supported natively in Windows Vista and Windows Server 2008 LANs. Both IPv4 and IPv6 are enabled by default. As a result of this dual-IP architecture, computers can use IPv6 to communicate if the client, server, and network infrastructure support it but also communicate with computers or network services that support only IPv4.
Layer 4
Layer 4, or the Transport Layer of the TCP/IP model, is the step in the communication process during which the terms of sending and receiving data are determined. Layer 4 also serves to tag data as being destined for a general application, such as e-mail or the Web. TCP and UDP are the two Transport Layer protocols within the TCP/IP suite
. ■ TCP TCP receives data from the Application Layer and processes the data as a stream of bytes. These bytes are grouped into segments that TCP then numbers and sequences for delivery to a network host. TCP acknowledges received data and arranges for data to be resent when such an acknowledgment is not received. When TCP receives a stream of data from a network host, it sends the data to the application designated by the TCP port number. TCP ports enable different applications and programs to use TCP services on a single host. Each program that uses TCP ports listens for messages arriving on its associated port number. Data sent to a specific TCP port is thus received by the application listening at that port.
UDP Many network services (such as DNS) rely on UDP instead of TCP as a transport protocol. UDP enables fast transport of datagrams by eliminating the reliability features of TCP, such as delivery guarantees and sequence verification. Unlike TCP, UDP is a connectionless service that provides only best-effort delivery to network hosts. A source host that needs reliable communication must use either TCP or a program that provides its own sequencing and acknowledgment services.
Layer 7
Layer 7, or the Application Layer of the TCP/IP model, is the step in the communication process during which end-user data is manipulated, packaged, and sent to and from Transport Layer ports. Application Layer protocols often describe a user-friendly method of presenting, naming, sending, or receiving data over TCP/IP. Common examples of Application Layer protocols native to the TCP/IP suite include HTTP, Telnet, FTP, Trivial File Transfer Protocol (TFTP), Simple Network Management Protocol (SNMP), DNS, Post Office Protocol 3 (POP3), Simple Mail Transfer Protocol (SMTP), and Network News Transfer Protocol (NNTP).
TCP/IP Encapsulation
By encapsulating data with each of the four layers described above, TCP/IP creates a packet. In the figure, an e-mail message of “Hello” is encapsulated with POP3 email (Layer 7), TCP (Layer 4), IP (Layer 3), and Ethernet (Layer 2) headers.
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