Implementación de un sistema basado en un modelo de administración de mejora la comunicación

the physical infrastructure are finished. It is now time to move upward in the OSI ref­ erence model and select the protocols for the network and transport layers and above. There is no need to be concerned about protocol compatibility at this point, because all the data-link layer protocols in current use can function with any network/transport layer protocol combination.

After this lesson, you will be able to

■ Describe the circumstances under which you should use the three network/transport layer protocol options supported by Microsoft Windows operating systems

Estimated lesson time: 15 minutes

Windows Server 2003 (like all current Windows operating systems) includes support for three network/transport layer protocol combinations: TCP/IP, Internetwork Packet Exchange (IPX), and the NetBIOS Extended User Interface (NetBEUI). The operating systems can function with any or all of these protocols installed at the same time. TCP/ IP and IPX are both collections of protocols (called protocol suites) that function together to provide services that span several layers of the OSI reference model. Both TCP/IP and IPX include network and transport layer protocols, and depending on the functions a computer is performing, the services provided by the protocol suite can at times run all the way up to the application layer. NetBEUI is a monolithic protocol that provides basic network functionality but is not nearly as flexible as TCP/IP or IPX.

Using TCP/IP

TCP/IP is a large collection of protocols that provides a comprehensive array of network­ ing services in addition to basic Windows file sharing. For most network designers, the process of selecting protocols for the network and transport layers is a brief one, because TCP/IP is the only logical selection. Only TCP/IP provides the flexibility, expandability, and Internet compatibility that most networks require. The TCP/IP protocols were designed in the 1970s to support the experimental packet-switching network that even­ tually became the Internet. Because this network consisted of many different types of computers, the protocols were designed to be completely hardware-independent. This is why the TCP/IP protocols have their own independent addressing system.

The two primary protocols in the TCP/IP suite are the Internet Protocol (IP), which oper­ ates at the network layer, and the Transmission Control Protocol (TCP), which operates at the transport layer. There is a second transport-layer protocol called the User Datagram Protocol (UDP). Virtually all TCP/IP communications use the IP protocol at the network layer and either TCP or UDP at the transport layer (see Figure 1-6). In fact, the TCP/IP suite is named for the most commonly used combination of protocols.

TCP UDP Transport Layer

IP Network Layer

Figure 1-6 TCP/IP network and transport layer protocols

IP is the key protocol of the TCP/IP suite. Almost all TCP/IP traffic is carried using IP packets called datagrams. An IP datagram is something like the envelope you use to mail a letter. The datagram has the address of the intended recipient and the address of the sender. As the packet travels across the network, computers read the recipient’s address and pass the packet along toward its intended destination. IP is also responsi­ ble for routing packets across an internetwork.

Whether a network communication process uses IP with TCP or IP with UDP depends on the requirements of the application generating the network traffic. TCP is a connection-oriented protocol, which means that before two computers can commu­ nicate, they exchange a series of messages that establish a connection between them. In addition, the computers acknowledge the data packets they receive from each other, ensuring that the transmitted data arrives intact. Computers use TCP when they have to transmit relatively large amounts of data that must arrive intact at the destination. The drawback to using TCP is the additional traffic generated by the connection establish­ ment and acknowledgment messages.

UDP is a connectionless protocol, which means that two computers can communicate without establishing a connection first, and they do not transmit dedicated acknowl­ edgment messages. Computers typically use UDP for brief exchanges of data, such as request and response messages, or for data transmissions that can survive the loss of an occasional packet, such as streaming audio or video. The advantage of using UDP is that its overhead is much lower than that of TCP.

In addition to these three primary protocols, the TCP/IP suite includes many others, spanning the OSI reference model from the data-link to the application layer, and providing a number of different administrative functions. When you configure a com­ puter to use TCP/IP, you install the entire suite of protocols at once. In the Windows Server 2003 operating system, the TCP/IP protocol suite takes the form of a single mod­ ule that you install in the Network Connections tool. The process is similar in other ver­ sions of the Windows operating system.

TCP/IP is unquestionably the industry standard in network/transport layer proto­ cols, and it provides all the functionality that any network design could require. When designing a network, the primary drawback to selecting TCP/IP is the individual

configuration required for each computer. On a TCP/IP network, every computer must have a unique IP address in addition to other configuration parameters. Orig­ inally, administrators had to individually configure each computer by hand, but today, technologies such as the Dynamic Host Configuration Protocol (DHCP) can automate the TCP/IP configuration process.

See Also See Chapter 2, “Planning a TCP/IP Network Infrastructure,” for more information about IP addressing and TCP/IP configuration.

Using IPX

IPX is also a suite of protocols that provides some of the same basic communications features as TCP/IP. The IPX protocols were developed by Novell for use with their Net- Ware operating system. Until the release of NetWare version 5 in 1998, computers had to use IPX to communicate with NetWare servers. However, NetWare 5 included sup- port for TCP/IP, and it is now possible to eliminate IPX from a NetWare network. Unlike the TCP/IP standards, which are in the public domain, the IPX standards are privately owned by Novell, who does not make them available to outside software developers. As a result, Microsoft developed its own version of the IPX protocols, called NWLink, to provide the Windows operating systems with NetWare connectivity. Windows Server 2003 still includes support for NWLink, in the form of a protocol module called NWLink IPX/SPX/Net- BIOS Compatible Transport Protocol, as do the other Windows operating systems.

The IPX suite, like TCP/IP, consists of several different protocols. IPX itself is the net- work layer protocol that carries most of the suite’s traffic. Sequenced Packet Exchange (SPX) is a connection-oriented transport layer protocol that is the IPX equivalent of TCP, and the NetWare Core Protocol (NCP) is roughly the equivalent of UDP.

The primary difference between the IPX protocol suite and TCP/IP is that IPX is designed for use on personal computer LANs only, while TCP/IP can support a net- work of any type and any size. One reason is that IPX does not have a self-contained addressing system, as TCP/IP does. IPX uses the hardware address coded into each computer’s network interface adapter to identify that system on the network.

Although it is possible to use the IPX protocols alone for Windows file sharing, few network administrators do this. IPX does not provide the Internet connectivity that most networks need. In most cases, administrators use IPX only for NetWare connec­ tivity in cases where all NetWare servers are not and cannot be configured to use TCP/ IP. For example, if a network still has a few old NetWare version 3.x servers that users need to access occasionally, the design might call for the installation of the IPX proto­ cols on the workstations, but in most cases the computers will have TCP/IP or NetBEUI installed as well for native Windows communications.

Using NetBEUI

NetBEUI was the default networking protocol of the Windows NT 3.1 and Windows for Workgroups operating systems when these systems were first released in 1993. At the time, PC networking was in its infancy; networks were relatively small and centrally located. NetBEUI uses the NetBIOS namespace to identify the computers on a network, a practice that Windows retained until the release of Windows 2000, which switched to the DNS namespace. Windows Server 2003 still includes support for NetBIOS naming, but the operating system no longer includes the NetBEUI protocol module.

Tip Although Windows Server 2003 does not include NetBEUI, there are still occasions when you might want to install the protocol, such as for testing whether a network communications problem is being caused by a TCP/IP configuration error or a network hardware fault. You can still install the NetBEUI module on a Windows Server 2003 computer, using the installation files included with Windows XP Professional or Windows XP Home Edition. These files are located in the \Valueadd\Msft\Net\Netbeui folder on the Windows XP distribution CD-ROM.

NetBEUI is a relatively simple networking protocol that provides basic file sharing ser­ vices for Windows computers. NetBEUI is a single protocol—not a suite—and does not require any individual configuration, as TCP/IP does. This is because NetBEUI uses the NetBIOS name specified by the installer during the Windows Setup procedure as the computer’s identifier on the network. NetBEUI also cannot provide Internet connectiv­ ity as TCP/IP can.

NetBEUI is intended for use on small LANs and is not suitable for a large enterprise net- work. This is because the NetBEUI protocol cannot route traffic between networks and therefore cannot support internetwork traffic. Both TCP/IP and IPX use separate iden­ tifiers for the network and for the individual computers on the network. A single IP address contains both a network and a host identifier. IPX uses the hardware address to identify the computer, and the NetWare installer assigns another address to each individual network. Therefore, both TCP/IP and IPX traffic can be addressed to a spe­ cific computer on a specific network anywhere in the enterprise.

The only identifier that NetBEUI uses is the computer’s NetBIOS name. This name identifies the computer on the network, but there is no identifier for the network itself. NetBEUI therefore cannot address traffic to a specific computer on another network.

Planning If you are designing a network that consists of a single LAN, such as for a home or a small business, NetBEUI is a suitable choice. However, if you are designing an internet- work, or if your computers need access to the Internet, you should not use NetBEUI.

Tip Although it might not be a suitable full-time protocol for your network, NetBEUI also has value as a troubleshooting tool. If you have computers on the same TCP/IP LAN that cannot communicate, and you suspect there might be a TCP/IP configuration problem, you can install NetBEUI on the computers as a test. If the computers can successfully communicate using NetBEUI, you know that the networking hardware is functioning properly and the prob­ lem lies somewhere in the TCP/IP installation or configuration.

Lesson Review

The following questions are intended to reinforce key information presented in this lesson. If you are unable to answer a question, review the lesson materials and try the question again. You can find answers to the questions in the “Questions and Answers” section at the end of this chapter.

1. Which of the following network/transport layer protocols can you use for Windows file sharing when installed alone?

a. TCP/IP only

b. TCP/IP and NetBEUI only

c. TCP/IP and IPX only

d. TCP/IP, IPX, and NetBEUI

2. Under what conditions would a network designer be obliged to install the IPX protocol suite on workstations using Windows operating systems?

3. Which of the following are connection-oriented protocols? (Choose all that apply.)

a. NetWare Core Protocol (NCP)

b. Transmission Control Protocol (TCP)

c. Sequenced Packet Exchange (SPX)

d. User Datagram Protocol (UDP)

Lesson Summary

■ TCP/IP is the industry standard protocol suite at the network and transport layers. Because it has a self-contained addressing system, TCP/IP can support any type of computer network and is expandable to almost any size.

■ The IPX protocol suite is designed for use with the Novell NetWare operating sys­ tem, but Windows can also use it for its own file sharing.

■ NetBEUI is a relatively simple protocol that supports Windows file sharing on small net- works, but it is not routable and is therefore unsuitable for internetwork installations.