Nov 24, 2013 ~ Network Services

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Network+™ "Quoting one of e-books" Chapter 3 : TCP/IP Fundamentals Introducing TCP/IP A Brief History of TCP/IP ...

Review Questions 1. Which layer of the OSI model ensures reliable, end-to-end communications? A. Network B. Transport C. Session D. Presentation 2. Which layer of the OSI model provides routing functionality? A. Transport B. Data Link C. Physical D. Network 3. Which layer of the OSI model translates the data from upper-layer protocols into electrical...

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Answers to Review Questions 1. B. Of the layers listed, the only OSI layer that is responsible for reliable end-to-end communications is the Transport layer. The Network layer is responsible for logical network addresses, the Session layer is responsible for opening sessions and maintaining session information, and the Presentation layer...

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Exam Essentials Be able to specify the main features—including speed, access method, topology, and media—of various network technologies, such as 802 standards and FDDI. You should be able to differentiate between the various networking technologies when studying for the exam. Refer to Table 2.3 for help. Be able to identify a MAC...

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AppleTalk and AppleTalk over IP When Apple introduced the Macintosh in 1984, the Mac included networking software. This networking software used a protocol known as AppleTalk and a cabling system known as LocalTalk. It is a very simple and elegant protocol in that...

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Summary In this chapter, you learned about the OSI model and had an introduction to a few of the most popular protocols in use today. You also learned about the seven layers that make up the OSI model, which are (from top to bottom) the Application, Presentation, Session, Transport, Network, Data Link, and Physical layers. In addition, you...

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NetBEUI NetBEUI is a Network layer protocol designed to provide support for NetBIOS networks. Net- BIOS is a protocol that was developed by IBM (and later enhanced by Microsoft and Novell) for use with network-aware operating systems like LAN Manager/LAN Server, Windows 9x, and Windows NT, 2000, XP, and 2003. It is a very fast and efficient...

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The Presentation Layer The Presentation layer does what you might think it does: It changes the look, or presentation, of the data from the lower layers into a format that the upper-layer processes can work with. Among other services, the Presentation layer deals with encryption, data compression, and network redirectors. ...

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The OSI Model’s Upper Layers The upper layers of the OSI model deal with less esoteric concepts. Even though we’re still discussing computer networking, the top three layers (Session, Presentation, and Application) seem easier to understand. Because the Network+ exam doesn’t cover the upper layers (and many times these top three layers are...

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The Session Layer Protocols that operate at the Session layer of the OSI model are responsible for establishing, maintaining, and breaking sessions, or dialogs. This is different from the connection services provided at the Transport layer because the Session layer operates at a higher level and looks at the bigger picture— the entire conversation,...

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The Application Layer Now, you might be thinking, “This layer is for my programs, right?” Wrong. The Application layer defines several standard network services that fall into categories such as file transfer, print access, and e-mail relay. The applications that access these network services are located above the Application layer and...

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Upper-Layer Devices There are only a few upper-layer devices, none of which operate at any specific layer. Because they perform a range of functions for the network, they fall into the class of devices known as gateways. A gateway translates one type of network data into another. Gateways can be either hardware or software, but the most...

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Networking Protocols Now that you have a basic understanding of the OSI model and its related concepts, you can use these concepts to understand how the major protocols work and how each of the protocols within each protocol stack maps to the OSI model, thus describing its function. In the following sections, you will...

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Review Questions
1. Which layer of the OSI model ensures reliable, end-to-end communications?
A. Network
B. Transport
C. Session
D. Presentation

2. Which layer of the OSI model provides routing functionality?
A. Transport
B. Data Link
C. Physical
D. Network

3. Which layer of the OSI model translates the data from upper-layer protocols into electrical signals and places them on the network media?
A. Physical
B. Transport
C. Data Link
D. Network

4. You are a consultant designing a network for a company with more than 1000 users. Which 802 standard would you implement to ensure that bandwidth would be sufficient and equal without bridging or additional segments?
A. 802.1
B. 802.2
C. 802.3
D. 802.5

5. Which one of the following devices will not propagate broadcasts from one of its interfaces to another?
A. Hub
B. Switch
C. Repeater
D. Router

6. You are installing a Windows XP–based TCP/IP network. You accidentally set workstation B to the same IP address as workstation A. Which workstation(s) will receive an error message?
A. Workstation A
B. Workstation B
C. Neither
D. Both

7. You are installing a Windows XP–based TCP/IP network. You accidentally set workstation B to the same IP address as workstation A. Which workstation(s) will have a valid IP address?
A. Workstation A
B. Workstation B
C. Neither
D. Both

8. Which device increases the number of collision domains while decreasing the average number of nodes per collision domain?
A. Hub
B. Transceiver
C. Switch
D. NIC

9. Which of the following protocols use a connectionless transport? (Choose all that apply.)
A. HTTP
B. TCP
C. TFTP
D. IP
E. NetBIOS

10. Which protocols use a connection-oriented transport?
A. UDP
B. NetBIOS
C. HTTP
D. TFTP

11. Which name resolution system is implemented with TCP/IP by default?
A. DNS
B. NDS
C. SND
D. WINS

12. Which OSI model layer has both a MAC sublayer and an LLC sublayer?
A. Physical
B. Transport
C. Network
D. Data Link

13. Which OSI model layer is responsible for establishing, maintaining, and breaking down dialog?
A. Application
B. Gateway
C. Session
D. Network

14. Which OSI layer is responsible for formatting data based on a standard syntax and for character- set conversion?
A. Transport
B. Network
C. Presentation
D. Session

15. Which OSI layer is responsible for building and tearing down packets?
A. Network
B. Transport
C. Data Link
D. Physical

16. The two halves of a MAC address are referred to as the
A. TCP and IP
B. OUI and device ID
C. OUI and IP
D. Device ID and IP

17. Which of the following directory services are hierarchical in design? (Choose all that apply.)
A. Novell NetWare Bindery
B. Microsoft Windows AD
C. Linux password shadow file
D. NT domain

18. You are the administrator of a 100-node Ethernet network. Your users are complaining of slow network speeds. What could you replace your hub with to increase your network throughput?
A. Router
B. Bridge
C. Switch
D. NIC

19. At which OSI model layer do routers primarily operate?
A. Physical
B. Data Link
C. Transport
D. Network

20. Which of the following is a MAC address?
A. 199.165.217.45
B. 00076A:01A5BBA7FF60
C. 01:A5:BB:A7:FF:60

D. 311 S. Park St.

Answers to Review Questions

1. B. Of the layers listed, the only OSI layer that is responsible for reliable end-to-end communications is the Transport layer. The Network layer is responsible for logical network addresses,
the Session layer is responsible for opening sessions and maintaining session information, and the Presentation layer is responsible for how data “looks” to the upper layer(s).

2. D. Of the OSI model layers listed, the Network layer is the only one that is responsible for routing information because it contains information for logical network addressing.

3. A. The Physical layer, as its name suggests, is the layer responsible for placing electrical transitions on the physical media. The other layers are all upper layers.

4. D. The 802.5 standard is similar to the Token Ring technology developed by IBM. That technology scales well and could handle more than 1000 users without bridging or additional segments.
Also, the performance would be better than that of any of the other technologies listed.

5. D. Routers will not propagate broadcasts from one of their ports to another. The other devices will. Each interface on a router is in a different broadcast domain.

6. D. By sending out packets to their own IP address, both workstations will detect if there is a duplicate IP address on the network and will display error messages to that effect.

7. A. Because workstation A had a valid IP address to begin with, Windows takes a first come, first served approach with the IP addresses and lets workstation A keep its IP address. Workstation
B detects that A already has it and just deactivates its own IP stack.

8. C. Each port on a switch belongs to a different collision domain, such that any device attached to one port on the switch cannot be involved in a collision with a device attached to a different
port on the switch. Inserting a switch into a LAN segment serves the purpose of increasing the number of collision domains and reducing the average number of nodes per collision domain.

9. C, E. TFTP and NetBIOS both use a connectionless transport (UDP and NetBEUI, respectively). TCP is, in fact, a connection-oriented transport protocol. HTTP uses TCP, so it is therefore connection oriented. And IP is a Network layer protocol.

10. C. Of all the protocols listed, HTTP is the only one that uses a connection-oriented Transport layer protocol (TCP). The others use, or are themselves, connectionless Transport layer protocols.
11. A. Although WINS is a name resolution that does translate NetBIOS names to IP addresses, it works only on Windows-based networks. The only true name resolution system that almost
every TCP/IP network uses is DNS.

12. D. The Data Link layer is divided into two sublayers: the MAC sublayer and an LLC sublayer. The other layers aren’t normally subdivided.

13. C. The Session layer is responsible for establishing, maintaining, and breaking down dialog.

14. C. The Presentation layer handles such services as data formatting, compression, encryption, and data-set conversion, such as from ASCII to Unicode or EBCDIC.

15. A. The Network layer is responsible for packaging data into packets. Different terms for data packages (such as frames) are used when discussing the other layers.

16. B. The first half of the MAC address is the Organizationally Unique Identifier (OUI), and the second half is the device ID.
17. B, C. Of the directory services listed, only Microsoft’s Active Directory and the Linux password shadow file are hierarchical in design.

18. C. A switch would increase performance by making virtual, direct connections between sender and receiver. Bridges and routers actually decrease performance because these devices introduce latency into the communication. Replacing the hub with an NIC just can’t be done.

19. D. Because routers deal with logical network addresses, they operate at the Network layer.

20. C. MAC addresses use a 12-digit hexadecimal number that is separated into six pairs of hex numbers. The only one that corresponds to that format is Answer C.

Exam Essentials
Be able to specify the main features—including speed, access method, topology, and media—of various network technologies, such as 802 standards and FDDI. You should be able to differentiate between the various networking technologies when studying for the exam. Refer to Table 2.3 for help.

Be able to identify a MAC address. A MAC address on a network is a 12-digit hexadecimal number in the format xx:xx:xx:xx:xx:xx, where x is a number from 0 to 9 or a letter from A to F.

Be able to identify the seven layers of the OSI model and describe their functions.
The seven layers of the OSI model (from the bottom to top—or layer 1 to layer 7) are the Physical layer, Data Link layer, Network layer, Transport layer, Session layer, Presentation layer, and Application layer.

Know how to differentiate between the IP, IPX, NetBEUI, and AppleTalk/AppleTalk over IP protocols when it comes to routing, addressing schemes, interoperability, and naming conventions.
TCP/IP uses the likes of RIP or OSPF as routing protocols, uses a dotted decimal notation (four sets of numbers, each from 0 to 255) for the addressing, is completely interoperable,
and uses DNS for host naming.

IPX, on the other hand, uses IPX RIP and NLSP for routing information, uses a unique 20-digit address (incorporating the MAC address) for the station address, interoperates with several different
operating systems (but not as many as TCP/IP), and uses NDS for host naming.

NetBEUI isn’t routable or as flexible, nor does it have as many features, but it does offer performance on a LAN segment. Addressing and naming are completely automatic (naming does
require a user to enter a computer name).
Finally, AppleTalk does have routing protocols (RTMP) and uses an automatic addressing scheme. It requires only that the user name the computer when enabling AppleTalk. It is by far the simplest protocol, but it has the lowest performance and the least interoperability. Apple-Talk over IP is a form of tunneling for AppleTalk traffic so AppleTalk devices across the Internet can communicate using that public network, but AppleTalk itself is compatible with neither IP nor the Internet.

Be able to explain the issues that must be considered when multiple protocols are running at the same time. When running multiple protocols, not only are you using more memory on a computer, you’re adding a level of complexity to the network that is multiplied by the number of stations that you add. It is better to run the fewest protocols possible. Some issues you will see include running out of memory, program confusion, stations unable to communicate (each is running a different protocol), and network congestion.

Identify the OSI layers at which hubs, switches, bridges, WAPs, routers, and network interface cards operate. Hubs operate at the Physical layer for the most part. Switches can operate at
many different layers (up to layer 5), but the lowest common denominator for all network switches is OSI layer 2 (Data Link layer). Bridges are relatively simple devices and operate primarily
at the Data Link layer. Routers are more complex devices, but because all they do is route packets, they operate at layer 3 (Network layer). Finally, network interface cards (NICs) operate

at the Physical and Data Link layers.

Review Questions

1. Which layer of the OSI model ensures reliable, end-to-end communications?
A. Network
B. Transport
C. Session
D. Presentation

2. Which layer of the OSI model provides routing functionality?
A. Transport
B. Data Link
C. Physical
D. Network

3. Which layer of the OSI model translates the data from upper-layer protocols into electrical signals and places them on the network media?
A. Physical
B. Transport
C. Data Link
D. Network

4. You are a consultant designing a network for a company with more than 1000 users. Which 802 standard would you implement to ensure that bandwidth would be sufficient and equal without bridging or additional segments?
A. 802.1
B. 802.2
C. 802.3
D. 802.5

5. Which one of the following devices will not propagate broadcasts from one of its interfaces to another?
A. Hub
B. Switch
C. Repeater
D. Router

6. You are installing a Windows XP–based TCP/IP network. You accidentally set workstation B to the same IP address as workstation A. Which workstation(s) will receive an error message?
A. Workstation A
B. Workstation B
C. Neither
D. Both

7. You are installing a Windows XP–based TCP/IP network. You accidentally set workstation B to the same IP address as workstation A. Which workstation(s) will have a valid IP address?
A. Workstation A
B. Workstation B
C. Neither
D. Both

8. Which device increases the number of collision domains while decreasing the average number of nodes per collision domain?
A. Hub
B. Transceiver
C. Switch
D. NIC

9. Which of the following protocols use a connectionless transport? (Choose all that apply.)
A. HTTP
B. TCP
C. TFTP
D. IP
E. NetBIOS

10. Which protocols use a connection-oriented transport?
A. UDP
B. NetBIOS
C. HTTP
D. TFTP

11. Which name resolution system is implemented with TCP/IP by default?
A. DNS
B. NDS
C. SND
D. WINS

12. Which OSI model layer has both a MAC sublayer and an LLC sublayer?
A. Physical
B. Transport
C. Network
D. Data Link

13. Which OSI model layer is responsible for establishing, maintaining, and breaking down dialog?
A. Application
B. Gateway
C. Session
D. Network

14. Which OSI layer is responsible for formatting data based on a standard syntax and for character- set conversion?
A. Transport
B. Network
C. Presentation
D. Session

15. Which OSI layer is responsible for building and tearing down packets?
A. Network
B. Transport
C. Data Link
D. Physical

16. The two halves of a MAC address are referred to as the
A. TCP and IP
B. OUI and device ID
C. OUI and IP
D. Device ID and IP

17. Which of the following directory services are hierarchical in design? (Choose all that apply.)
A. Novell NetWare Bindery
B. Microsoft Windows AD
C. Linux password shadow file
D. NT domain

18. You are the administrator of a 100-node Ethernet network. Your users are complaining of slow network speeds. What could you replace your hub with to increase your network throughput?
A. Router
B. Bridge
C. Switch
D. NIC

19. At which OSI model layer do routers primarily operate?
A. Physical
B. Data Link
C. Transport
D. Network

20. Which of the following is a MAC address?
A. 199.165.217.45
B. 00076A:01A5BBA7FF60
C. 01:A5:BB:A7:FF:60

D. 311 S. Park St.

AppleTalk and AppleTalk over IP
When Apple introduced the Macintosh in 1984, the Mac included networking software. This networking software used a protocol known as AppleTalk and a cabling system known as LocalTalk. It is a very simple and elegant protocol in that the computer takes care of most of the configuration. You simply plug it in and it works. Because of its simplicity and popularity with Mac users, and because the Mac users wanted a faster version, Apple developed Apple- Talk version 2 with support for Ethernet (EtherTalk). Figure 2.20 illustrates the interrelationships between these components of AppleTalk, as well as others we’ll discuss. Table 2.5 descibes the protocols shown in Figure 2.20.

FIGURE 2 . 2 0 The AppleTalk protocol model

TABLE 2 . 5 AppleTalk Protocols Defined

Protocol

Description

Datagram Delivery
Protocol (DDP)    Delivers data in discrete packets. DDP is unreliable, not acknowledging
data delivery or guaranteeing the order of its delivery.

Routing Table Maintenance Protocol (RTMP) Establishes and maintains routing tables through the exchange of routing information between routers.

AppleTalk Echo
Protocol (AEP) Provides a way to test for responsiveness and round-trip transmission
times. Similar to using ICMP for Pinging remote devices.

AppleTalk Transaction
Protocol (ATP) Provides reliable data transmission, similar to the way in which
TCP does so for TCP/IP.

Name Binding
Protocol (NBP) Translates an AppleTalk device name into an AppleTalk network
address.

AppleTalk Data Stream
Protocol (ADSP) Establishes an end-to-end full-duplex session to exchange data
between two network applications in which both endpoints have
equal control over the communication.

Zone Information
Protocol (ZIP) Maintains AppleTalk internetwork-wide mappings of zone names
to network number ranges on routers. While ZIP is primarily implemented by routers, end devices implement a portion of ZIP, allowing them to obtain zone information from a router. A zone is similar, in purpose, to a VLAN in layer 2 switching, unifying nodes by departmental membership or other logical affiliations regardless of their physical LAN segment connectivity.

AppleTalk Session
Protocol (ASP) Establishes reliable sessions that provide for non-duplicate transmissions
between an ASP workstation process and an ASP server process. Unlike those formed in ADSP, ASP sessions are asymmetrical in that an ASP server never initiates communication but only responds to communication initiated by the ASP workstation.

Printer Access Protocol Handles connection setup, maintenance, and termination of reliable transmission of messages to printers.

AppleTalk Filing
Protocol (AFP) Provides the interface between an application and a file server.
Allows an application on an AppleTalk workstation to access and manipulate files on an AFP file server, such as an AppleShare server or a Microsoft Windows server running AFP, in the form of Services for Macintosh.

Apple’s Mac OS X and OS X Panther (versions 10.3.x) can communicate with any server running the AFP service, whether over TCP/IP, which is preferred by Apple, or over the legacy Apple- Talk protocol. On Macintosh servers, the AFP service is implemented as AppleShare. You can use IP to connect to Macintosh file services running on Mac OS X Server, AppleShare IP, and Windows 2000 and later servers. AppleShare IP has been an add-on service available since the Mac OS 8 days, necessary for IP connectivity with AFP resources before this functionality became available natively in Mac OS X. Of course, Mac OS X still is capable of communicating with AFP servers over AppleTalk instead of IP, supporting legacy access to older AppleShare servers and Windows NT servers that only provide Mac file services over AppleTalk. However, Apple recommends migrating to TCP/IP as the transport method between clients and AFP servers.

Note:

One note about Mac OS X and AppleTalk: While Mac OS X clients can still use
AppleTalk to communicate with older AppleShare servers, Mac OS X servers
do not support client communication to their Apple File Services (the server’s
instance of AFP) via AppleTalk. While the Mac OS X server advertises its services
over AppleTalk for older clients to be able to show the server in their
Chooser, connection to the server must be via TCP/IP.

Note:

In addition to using AppleTalk for service browsing, you can use Mac OS X
Server’s Server Admin utility to enable Apple File Service browsing via Network
Service Locator (NSL) and Rendezvous. Rendezvous is an IP-based open
service discovery protocol, allowing devices to be added to and removed from
networks without configuration. Rendezvous is mentioned in Chapter 3’s Zero-
Conf discussion.

Services for Macintosh
Although the Windows 2000 file system is fairly different from the Macintosh file system, files on a Windows 2000 Server machine are accessible by both Windows 2000 clients and Macintosh
clients. Services for Macintosh works in the background on a Windows 2000 Server machine to make this multiclient support possible by establishing an AFP-compatible server service. Files can be made to appear as they usually do for both Macintosh and Microsoft clients. A Microsoft client sees files represented as a directory tree, while a Macintosh client sees files represented as a Macintosh folder. In this environment, files may be stored in shared folders or Macintosh volumes. Macintosh volumes that are shared to the network are seen only by Macintosh clients, not by the Windows 2000 clients. Conversely, in order for a Macintosh
client to gain access to a Microsoft shared folder, the administrator must designate the folder as a Macintosh-accessible volume.

For folders that are both a Microsoft shared folder and a Macintosh-accessible volume, both Microsoft clients and Macintosh clients have access to the resource. However, while Microsoft clients see folders and files as they are stored on the server’s hard disk beneath the root of the share, Macintosh clients see the volume as containing Macintosh files and folders.
The following sections cover AppleTalk’s methods of addressing and naming as well as its ability to be routed over internetworks.

Addressing
Each station on an AppleTalk network uses an address that is 24 bits long. Sixteen of those bits are given to the network, and each network can support 254 nodes. Each network segment can
be given either a single 16-bit network number or a range of 16-bit network numbers. If a network is assigned a range of numbers, that network is considered an Extended AppleTalk network because it can support more than 254 nodes. The node address is automatically assigned by the computer itself.
In addition to network numbers, AppleTalk networks use areas called zones. Zones allow an administrator to divide a network into logical areas for easier administration and to make it easier

for a user to find resources.

Note:

Although you can have multiple zones on an AppleTalk network, an AppleTalk node can belong to only one zone.

Routing
AppleTalk wasn’t originally designed to be routed over a WAN, but with the release of AppleTalk version 2, Apple included routing functionality with the introduction of the Routing Table Maintenance Protocol (RTMP). RTMP is a distance vector routing protocol, like RIP, for both IP and IPX.

Interoperability
The only computer that comes with AppleTalk installed by default is the Macintosh. Most Windows operating systems are able to use the AppleTalk protocol but require that additional software
be installed. By using AppleTalk over IP, it is possible to tunnel AppleTalk conversations over the very Internet itself. Two AppleTalk speakers can package their AppleTalk packets in
such a way that they are transmissible through IP intermediate systems, being stripped back down to the original AppleTalk packet by the receiving AppleTalk-speaking device.

Naming
AppleTalk uses the Name Binding Protocol (NBP) to associate the name of the computer with its network address. It is broadcast based. Every station broadcasts its name when it comes up on a network. The AppleTalk router on a network will cache these names and respond when a node requests a name resolution; the local router will answer with information it has obtained from this NBP cache.

Note:

If an AppleTalk network doesn’t have a router, each node will perform both its normal NBP requests and any NBP responses to broadcasted requests for its own AppleTalk address.

Summary
In this chapter, you learned about the OSI model and had an introduction to a few of the most popular protocols in use today. You also learned about the seven layers that make up the OSI
model, which are (from top to bottom) the Application, Presentation, Session, Transport, Network, Data Link, and Physical layers. In addition, you learned what each layer’s primary responsibility is and in what layer certain popular protocols function. This chapter also reiterated at which layers certain common devices operate. This chapter included discussions of some of the major protocol suites, including TCP/IP, IPX/SPX, NetBEUI/NetBIOS, and AppleTalk, and how the different protocols of each suite work together. For each protocol, you learned which parts of the protocol stack handle the concepts of addressing, routing, interoperability, and naming. Also in this chapter, you were introduced to popular Data Link technologies, including those
in the 802 standards track of IEEE, such as Ethernet and Token Ring, as well as their media access methodologies, such as CSMA/CD and token passing. On a related note, you were given

the details of the structure and use of the 48-bit MAC address.

NetBEUI
NetBEUI is a Network layer protocol designed to provide support for NetBIOS networks. Net- BIOS is a protocol that was developed by IBM (and later enhanced by Microsoft and Novell)
for use with network-aware operating systems like LAN Manager/LAN Server, Windows 9x, and Windows NT, 2000, XP, and 2003. It is a very fast and efficient protocol with low overhead.
Because NetBIOS is small and efficient, it works well on small LANs with between 10 and 200 nodes. The two protocols are often referred to together as NetBEUI/NetBIOS. In the following sections, naming, addressing, routing, and interoperability will be presented for NetBEUI, as it was for IPX/SPX and TCP/IP.

Naming and Addressing
There is very little network addressing with NetBEUI/NetBIOS. Actually, for NetBEUI, naming and addressing are the same thing. Each device, not interface, is configured with a unique name
(called the NetBIOS name) that is used for all communications. It’s simple and quick. The only item that must be configured on the workstation is the name of the workstation. NetBIOS names can be up to 15 characters in length and must adhere to special-character exclusions similar to those listed for IPX/SPX (NetWare).

Routing
Because the NetBEUI/NetBIOS protocol stack does not have an address structure with a hierarchical format and has no network and host boundaries, it is not a routable protocol. Routers
will drop NetBEUI/NetBIOS packets by default. Some routers, however, may be configured to bridge these packets to all segments or to unicast them to a specific IP address, which must be
configured on the receiving interface.

Interoperability
Only a few operating systems run NetBEUI/NetBIOS. The operating systems for IBM and Microsoft are the primary supporters of this protocol. Windows 9x, NT, and 2000/2003 and LAN Manager and OS/2 support NetBEUI/NetBIOS. These operating systems can therefore communicate using
NetBEUI/NetBIOS. The Macintosh operating system, however, does not support NetBEUI natively, nor do the latest implementations of Microsoft Windows, but you can add it back in, which, unless a strong case exists in favor of doing so, is highly frowned upon due to compatibility issues.

Note:

Note that the Apple Filing Protocol should be your certification focus and the
overall structure of the AppleTalk suite of protocols is provided for context.

The Presentation Layer
The Presentation layer does what you might think it does: It changes the look, or presentation, of the data from the lower layers into a format that the upper-layer processes can work with.
Among other services, the Presentation layer deals with encryption, data compression, and network redirectors.
In addition, the Presentation layer deals with character-set translation. Not all computer systems use the same table to convert binary numbers into text. Most standard computer systems use the American Standard Code for Information Interchange (ASCII). Mainframe computers (and some IBM networking systems) use the Extended Binary Coded Decimal Interchange Code (EBCDIC) and Unicode, which is popular on the Internet as one character set that assigns a
unique number to every character regardless of the language or the operating system used to display the character. The three are totally different. Protocols at the Presentation layer can translate
between the three.

The OSI Model’s Upper Layers
The upper layers of the OSI model deal with less esoteric concepts. Even though we’re still discussing computer networking, the top three layers (Session, Presentation, and Application)
seem easier to understand. Because the Network+ exam doesn’t cover the upper layers (and many times these top three layers are grouped together), the following sections will give only a brief overview.

The Session Layer
Protocols that operate at the Session layer of the OSI model are responsible for establishing, maintaining, and breaking sessions, or dialogs. This is different from the connection services provided at
the Transport layer because the Session layer operates at a higher level and looks at the bigger picture— the entire conversation, not just one sentence. Many gateways operate at the Session layer.
Novell’s Service Advertisement Protocol (SAP) is a Session layer protocol, as well as NetBIOS.

The Application Layer
Now, you might be thinking, “This layer is for my programs, right?” Wrong. The Application layer defines several standard network services that fall into categories such as file transfer, print access, and e-mail relay. The applications that access these network services are located above the Application layer and are not even part of the layered model.

Upper-Layer Devices
There are only a few upper-layer devices, none of which operate at any specific layer. Because they perform a range of functions for the network, they fall into the class of devices known as
gateways. A gateway translates one type of network data into another. Gateways can be either hardware or software, but the most popular way to run a gateway is as a software program on
a dedicated computer.
There are many, many types of gateways, but the one most people think of is an e-mail gateway. E-mail gateways translate e-mail messages from one type of e-mail system so that they can
be transmitted on another (for example, from GroupWise e-mail to SMTP mail for the Internet).

Networking Protocols
Now that you have a basic understanding of the OSI model and its related concepts, you can use these concepts to understand how the major protocols work and how each of the protocols
within each protocol stack maps to the OSI model, thus describing its function.
In the following sections, you will learn about four major protocol stacks and how each one handles the concepts of addressing, routing, interoperability, and naming:

TCP/IP
IPX/SPX
NetBEUI
AppleTalk/AppleTalk over IP

Sunday, November 24, 2013

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Sunday, November 24, 2013

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