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Authoritative coverage of all exam objectives, including:
Implementing, managing, and maintaining IP addressing
Implementing, managing, and maintaining name resolution
Implementing, managing, and maintaining network security
Implementing, managing, and maintaining routing and remote access
Maintaining a network infrastructure
Featured on the CD
The enclosed CD is packed with vital preparation tools and materials, beginning with the Sybex test engine for exam 70-291. Loaded with hundreds of practice questions, it lets you test yourself chapter by chapter and review your score by objectives area. You’ll also find electronic flashcards for PCs, Pocket PCs, and Palm handhelds, two bonus exams that will help you prepare for the test, WinSim 2003 product simulation software, and a fully searchable electronic version of the book.
About the Authors
James Chellis, MCSE and MCT, is CEO of EdgeTek Education, a Microsoft Certified Solution Provider specializing in courseware development. Paul Robichaux is a noted networking expert and the author of more than 20 books, including MCSE: Windows 2000 Network Infrastructure Administration Study Guide also from Sybex. Matthew Sheltz, MCP, is a software engineer and systems administrator for EdgeTek Education.
Microsoft has put an immense amount of time and effort into building Windows Server 2003. It's not fair to say that this operating system is an entirely new product because it still retains a great deal of core code from Windows 2000 and even Windows NT, Internet Information Server, and Exchange Server. Windows Server 2003 is a large, complicated, and very powerful operating system. To use it effectively, you have to understand how it works and how to make it do what you want it to do. This book is a study guide for the Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure exam, so it makes sense to lead off with a discussion of the network protocols included in Windows Server 2003-what they're for, how they work, and what you can do with them.
Having a good frame of reference helps when comparing network protocols. To establish such a frame, this chapter will begin with the Open Systems Interconnection (OSI) network model, a sort of idealized way to stack various protocols together.
The OSI Model
The International Organization for Standardization (ISO) began developing the Open Systems Interconnection (OSI) reference model in 1977. It has since become the most widely accepted model for understanding network communication; once you understand how the OSI model works, you can use it to compare network implementations on different systems.
When you want to communicate with another person, you need to have two things in common: a communication language and a communication medium. Computer networks are no different; for communication to take place on a network composed of a variety of different network devices, both the language and medium must be clearly defined. The OSI model (and networking models developed by other organizations) attempts to define rules that cover both the generalities and specifics of networks:
How network devices contact each other and, if they have different languages, how they communicate with each other
Methods by which a device on a network knows when to transmit data and when not to
Methods to ensure that network transmissions are received correctly and by the right recipient
How the physical transmission media is arranged and connected
How to ensure that network devices maintain a proper rate of data flow
How bits are represented on the network media
The OSI model isn't a product. It's just a conceptual framework you can use to better understand the complex interactions taking place among the various devices on a network. It doesn't do anything in the communication process; appropriate software and hardware do the actual work. The OSI model simply defines which tasks need to be done and which protocols will handle those tasks at each of the seven layers of the model. The seven layers are as follows:
Application (layer 7)
Presentation (layer 6)
Session (layer 5)
Transport (layer 4)
Network (layer 3)
Data-Link (layer 2)
Physical (layer 1)
You can remember the seven layers using a handy mnemonic, such as "All Pitchers Sometimes Take Naps During Preseason."
Each of the seven layers has a distinct function, which we'll explore a little later in the chapter.
The OSI model splits communication tasks into smaller pieces called subtasks. Protocol implementations are computer processes that handle these subtasks. Specific protocols fulfill subtasks at specific layers of the OSI model. When these protocols are grouped together to complete a whole task, the assemblage of code is called a protocol stack. The stack is just a group of protocols, arranged in layers, that implements an entire communication process. Each layer of the OSI model has a different protocol associated with it. When more than one protocol is needed to complete a communication process, the protocols are grouped together in a stack. An example of a protocol stack is TCP/IP, which is widely used by Unix and the Internet-the TCP and IP protocols are implemented at different OSI layers.
Each layer in the protocol stack receives services from the layer below it and provides services to the layer above it. It can be better explained like this: Layer N uses the services of the layer below it (layer N - 1) and provides services to the layer above it (layer N + 1).
For two computers to communicate, the same protocol stacks must be running on each computer. Each layer on both computers' stacks must use compatible protocols in order for the machines to communicate with each other. The computers can have different operating systems and still be able to communicate if they are running the same protocol stacks. For example, a DOS machine running TCP/IP can communicate with a Macintosh machine running TCP/IP (see Figure 1.1).
The Physical Layer
The Physical layer is responsible for sending bits from one computer to another. Physical layer components don't care what the bits mean; their job is to get the bits from point A to point B, using whatever kind of optical, electrical, or wireless connection that connects the points. This level defines physical and electrical details, such as what will represent a 1 or a 0, how many pins a network connector will have, how data will be synchronized, and when the network adapter may or may not transmit the data (see Figure 1.2).
The Physical layer addresses all the minutiae of the actual physical connection between the computer and the network medium, including the following:
Network connection types, including multipoint and point-to-point connections.
Physical topologies, or how the network is physically laid out (e.g., bus, star, or ring topologies).
Which analog and digital signaling methods are used to encode data in the analog and digital signals.
Bit synchronization, which deals with keeping the sender and receiver in synch as they read and write data.
Multiplexing, or the process of combining several data channels into one.
Termination, which prevents signals from reflecting back through the cable and causing signal and packets errors. It also indicates the last node in a network segment.
The Data-Link Layer
The Data-Link layer provides for the flow of data over a single physical link from one device to another. It accepts packets from the Network layer and packages the information into data units called frames; these frames are presented to the Physical layer for transmission. The Data-Link layer adds control information, such as frame type, to the data being sent.
This layer also provides for the error-free transfer of frames from one computer to another. A cyclic redundancy check (CRC) added to the data frame can detect damaged frames, and the Data-Link layer in the receiving computer can request that the CRC information be present so that it can check incoming frames for errors. The Data-Link layer can also detect when frames are lost and request that those frames be sent again.
In broadcast networks such as Ethernet, all devices on the LAN receive the data that any device transmits. (Whether a network is broadcast or point-to-point is determined by the network protocols used to transmit data over it.) The Data-Link layer on a particular device is responsible for recognizing frames addressed to that device and throwing the rest away, much as you might sort through your daily mail to separate good stuff from junk. Figure 1.3 shows how the Data-Link layer establishes an error-free connection between two devices.
The Institute of Electrical and Electronics Engineers (IEEE) developed a protocol specification known as IEEE 802.X. (802.2 is the standard that divides this layer into two sublayers. The MAC layer varies for different network types and is described further in standards 802.3 through 802.5.) As part of that specification (which today we know as Ethernet), the Data-Link layer is split into two sublayers:
The Logical Link Control (LLC) layer establishes and maintains the logical communication links between the communicating devices.
The Media Access Control (MAC) layer acts like an airport control tower-it controls the way multiple devices share the same media channel in the same way that a control tower regulates the flow of air traffic into and out of an airport.
Figure 1.4 illustrates the division of the Data-Link layer into the LLC and MAC layers.
The LLC sublayer provides Service Access Points (SAPs) that other computers can refer to and use to transfer information from the LLC sublayer to the upper OSI layers. This is defined in the 802.2 standard.
The MAC sublayer, the lower of the two sublayers, provides for shared access to the network adapter and communicates directly with network interface cards. Network interface cards have a unique 12-digit hexadecimal MAC address (frequently called the hardware Ethernet address) assigned before they leave the factory where they are made. The LLC sublayer uses MAC addresses to establish logical links between devices on the same LAN.
The Network Layer
The Network layer handles moving packets between devices that are more than one link away from each other. It makes routing decisions and forwards packets as necessary to help them travel to their intended destination. In larger networks, there may be intermediate devices and subnetworks between any two end systems. The network layer makes it possible for the Transport layer (and layers above it) to send packets without being concerned with whether the end system is on the same piece of network cable or on the other end of a large wide area network.
To do its job, the Network layer translates logical network addresses into physical machine addresses (MAC addresses, which operate at the Data-Link layer). The Network layer also determines the quality of service (such as the priority of the message) and the route a message will take if there are several ways a message can get to its destination.
The Network layer also may split large packets into smaller chunks if the packet is larger than the largest data frame the Data-Link layer will accept. The network reassembles the chunks into packets at the receiving end.
Intermediate systems that perform only routing and relaying functions and do not provide an environment for executing user programs can implement just the first three OSI network layers. Figure 1.5 shows how the Network layer moves packets across multiple links in a network.
The Network layer performs several important functions that enable data to arrive at its destination. The protocols at this layer may choose a specific route through an internetwork to avoid the excess traffic caused by sending data over networks and segments that don't need access to it. The Network layer serves to support communications between logically separate networks. This layer is concerned with the following:
Addressing, including logical network addresses and services addresses
Circuit, message, and packet switching
Route discovery and route selection
Connection services, including Network layer flow control, Network layer error control, and packet sequence control
In Windows Server 2003, the various routing services for TCP/IP, AppleTalk, and Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) perform Network layer services (see Chapter 9, "Managing IP Routing," for more on these services). In addition, the TCP/IP, AppleTalk, and IPX stacks provide routing capacity for those protocols.
The Transport Layer
The Transport layer ensures that data is delivered error free, in sequence, and with no losses or duplications. This layer also breaks large messages from the Session layer into smaller packets to be sent to the destination computer and reassembles packets into messages to be presented to the Network layer. The Transport layer typically sends an acknowledgment to the originator for messages received (as in Figure 1.6).
The Session Layer
The Session layer allows applications on separate computers to share a connection called a session. This layer provides services, such as name lookup and security, that allow two programs to find each other and establish the communication link. The Session layer also provides for data synchronization and checkpointing so that in the event of a network failure, only the data sent after the point of failure would need to be resent. This layer also controls the dialog between two processes and determines who can transmit and who can receive at what point during the communication (see Figure 1.7).
The Presentation Layer
The Presentation layer translates data between the formats the network requires and the formats the computer expects. The Presentation layer performs protocol conversion; data translation, compression, and encryption; character set conversion; and the interpretation of graphics commands.
The network redirector, long a part of Windows networking, operates at this level. The redirector is what makes the files on a file server visible to the client computer. The network redirector also makes remote printers act as though they are attached to the local computer. Figure 1.8 shows the Presentation layer's role in the protocol stack.
The Application Layer
The Application layer is the topmost layer of the OSI model, and it provides services that directly support user applications, such as database access, e-mail, and file transfers. It also allows applications to communicate with applications on other computers as though they were on the same computer. When a programmer writes an application program that uses network services, this is the layer the application program will access. For example, Internet Explorer uses the Application layer to make its requests for files and web pages; the Application layer then passes those requests down the stack, with each succeeding layer doing its job (as in Figure 1.9).
Communication between Stacks
When a message is sent from one machine to another, it travels down the layers on one machine and then up the layers on the other machine, as shown in Figure 1.10.
As the message travels down the first stack, each layer it passes through (except the Physical layer) adds a header. These headers contain pieces of control information that are read and processed by the corresponding layer on the receiving stack. As the message travels up the stack of the other machine, each layer removes the header added by its peer layer and uses the information it finds to figure out what to do with the message contents (see Figure 1.11).
As an example, consider the network we're using while writing this book. It's a TCP/IP network containing several Windows 2000, Windows Server 2003, Macintosh, and Windows NT machines, all connected using the TCP/IP protocol. When we mount a share from our Windows Server 2003 file server on the Mac desktop, at layer 7, the Mac Finder requests something from the Windows Server 2003. This request is sent to the Mac's layer 6, which receives the request as a data packet, adds its own header, and passes the packet down to layer 5. At layer 5, the process is repeated, and it continues until the packet makes it to the Physical layer. The physical layer is responsible for actually moving the bits across the network wiring in the office, so it carries the request packet to a place where the Windows Server 2003 machine can "hear" it. At that point, the request packet begins its journey up the layers on the Windows Server 2003 file server. The header that was put on at the Data-Link layer of the Mac OS is stripped off at the Data-Link layer on the Windows Server 2003 machine. The Windows Data-Link layer driver performs the tasks requested in the header and passes the requests to the next, higher layer. This process is repeated until the Windows Server 2003 file server receives the packet and interprets the request. The Windows Server 2003 would then formulate an appropriate response and send it to the Mac.
Microsoft's Network Components and the OSI Model
Because the OSI model is so abstract, it can be hard to tell how its concepts relate to the actual network software and hardware you use in the real world. The following sections will make the link clearer. We will introduce you to the specific protocols that are included with Windows Server 2003 and see how they apply to the various layers of the OSI model.
Excerpted from MCSA/MCSE: Windows Server 2003 Network Infrastructure, Implementation, Management and Maintenance Study Guide by James Chellis Excerpted by permission.
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|Ch. 1||Understanding Windows Server 2003 Networking||1|
|Ch. 2||Installing and Configuring TCP/IP||47|
|Ch. 3||Administering Security Policy||97|
|Ch. 4||Managing IP Security||169|
|Ch. 5||Managing the Dynamic Host Configuration Protocol (DHCP)||221|
|Ch. 6||Installing and Managing Domain Name Service (DNS)||267|
|Ch. 7||Managing Remote Access Services||325|
|Ch. 8||Managing User Access to Remote Access Services||375|
|Ch. 9||Managing IP Routing||411|
If you have not done simulations or are not in a working environment with Server 2003... this may help for basic level foundation knowledge, but I was better off reviewing practice exam questions and actually exploring toolkits, command lines, services and protocols in order to actually pass the test.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted August 4, 2004
Due to the more focused topics of the previous exams, the previous books were adequete enough to get you ready for the tests. At this point however, the exam begins to deal with many different services over entire networks, so in order to pass, a fluent knowledge of how all the elements work together and good trouble shooting techniques are required and this book does not provide these.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.