The Transmission Control Protocol

The Transmission Control Protocol
TCP is the Transport layer of the protocol and serves to ensure a reliable, verifiable data exchange between hosts on a network. TCP breaks data into pieces, wraps the pieces with the information needed to identify it as a piece of the original message, and allows the pieces to be reassembled at the receiving end of the communications link. The wrapped and bundled pieces are called datagrams. Datagrams are also referred to as segments for TCP due to the way it often splits the original data into more manageable chunks. The most important information in the header includes the source and destination port numbers, a sequence number for the datagram, and a checksum.
      The source port number and the destination port number ensure that the data is sent back and forth to the correct application process running on each computer. The sequence number allows the datagrams to be rebuilt in the correct order in the receiving device, and the checksum allows the protocol to check whether the data sent is the same as the data received. It performs this last feat by running the bits of the segment through a complex polynomial expression and inserting the resulting number in the header. This is when IP enters the picture. Once the header is on the datagram, TCP passes the datagram to IP to be routed to its destination. The receiving device then performs the same calculation, and if the two calculations do not match, an error has occurred somewhere along the line and the datagram is silently discarded by the destination device and resent by the source device after its timer expires waiting for a positive acknowledgment that never arrives.

Figure 3.2 shows the layout of the datagram with the TCP header in place.

      In addition to the source and destination port numbers, the sequence number, and the checksum, a TCP header contains the following information:

Acknowledgment Number Indicates that the data was received successfully. If the datagram is damaged in transit, the receiver throws the data away and does not send an acknowledgment

back to the sender. After a predefined time-out expires, the sender retransmits the data for which no acknowledgment was received. Only positive forward acknowledgments are sent in TCP. Positive means that only successful transmissions are acknowledged. Forward means that the acknowledgment number represents the next sequence number the destination device expects to receive.

Offset Specifies the length of the header in 32-bit chunks.

Reserved This field specifies variables that are set aside for future use. This field must contain zeros. 

Flags These are six one-bit fields that indicate various things, such as whether this segment is the end of the higher-layer message, that the acknowledgment number is significant, that the sender is requesting that a virtual circuit with the receiver be established or torn down, or that the data in the segment is urgent.

Window Provides a way to increase the number of segments transmitted before the sender expects an acknowledgment, which improves efficiency in data transfers. Conversely, decreasing

the value of this field can indicate that network problems endanger the integrity of the data so more segments need to be acknowledged until conditions improve.

Urgent Pointer Gives the location in the segment where the urgent data ends, assuming the urgent data begins at the beginning of the segment. This allows out-of-band transmission of special

data, signifying to the receiving device that this data should be pushed ahead of any other that it has received but has not yet processed. Special data could include keyboard break sequences in

a Telnet session, which should immediately be processed by the receiving device in order to discontinue potentially harmful processing of previously received data. In light of this use, it makes

sense that the transmitting device would place such critical control information at the beginning of a new, emerging segment.

Options Communicates various parameters of the TCP virtual circuit. The only option originally specified in the TCP RFC (RFC 793) was maximum segment size, which has to be communicated
in the first segment during connection establishment. Later RFCs specify additional options. The latest list of TCP options can be found on the web site for the Internet Assigned Numbers Authority (www.iana.org/assignments/tcp-parameters).

Padding    Ensures that the header ends on a 32-bit boundary so that the offset field makes sense as a whole number. 

The data in the segment immediately follows this header information.


The Actual Use of TCP Communications
The following list summarizes the TCP process:

• Flow control allows two systems to cooperate in datagram transmission to prevent overflows and lost segments.
• Acknowledgment lets the sender know that the recipient has received the information.
• Sequencing ensures that segments arrive in the proper order.
• Checksums allow easy detection of corrupted segments.
• Retransmission of lost or corrupted segments is managed in a timely way.

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TCP/IP and the OSI Model

TCP/IP and the OSI Model
As you learned in Chapter 2, “The OSI Model,” the OSI model divides computer-to-computer communications into seven connected layers; TCP/IP uses the Department of Defense (DoD)
model, which describes communications in only four layers, as Figure 3.1 shows. Each successively higher layer builds on the functions provided by the layers below.

Note:

The DoD model has fewer layers than the OSI model has, but that does not mean that it has less functionality. We draw the models to the same height because all data communications functionality is there. The DoD model simply combines the functionality of those layers into “larger” layers whose protocols perform all related functions of the equivalent OSI layers. Remember, that’s part of the OSI reference model’s success. Even though the original protocols never really caught on, the model itself is at once generic in its description of
protocol functionality and specific in its separation of communications tasks into more layers than just about any other model.

FIGURE 3 . 1 A comparison of the seven-layer OSI model, the four-layer DoD model, and how TCP/IP maps to each model 

As you may remember from Chapter 2’s discussion of the OSI model, the layers are as follows:

Application Layer The highest layer; defines the manner in which applications interact with the network—including databases, e-mail, and terminal-emulation programs using Application layer protocols similar to Lightweight Directory Access Protocol (LDAP), Simple Mail Transfer Protocol (SMTP), and Telnet.

Presentation Layer Defines the way in which data is formatted, presented, converted, and encoded.

Session Layer Coordinates communications and maintains the session for as long as it is needed—performing security, logging, and administrative functions.

Transport Layer Defines protocols for structuring messages and supervises the validity of the transmission by performing error checking.

Network Layer Defines data-routing protocols to increase the likelihood that the information arrives at the correct destination node.

Data Link Layer Validates the integrity of the flow of the data from one node to another by synchronizing blocks of data and controlling the flow.

Physical Layer Defines the mechanism for communicating with the transmission medium and the interface hardware.

Note:

Although no commercially available networking protocol suite follows the OSI model exactly, most perform all the same functions.

In the DoD model, the four layers are as follows:

Process/Application Layer The highest layer; applications such as FTP, Telnet, and others interact through this layer. Corresponds to the top three layers of the OSI model.

Host-to-Host Layer TCP and UDP add transport control information to the user data. Corresponds to the Transport layer of the OSI model.

Internet Layer Adds IP information to form a packet. Corresponds to the Network layer of the OSI model.

Network Access Layer Defines the mechanism for communicating with the transmission medium and the interface hardware. Corresponds to the bottom two layers of the OSI model.

Each layer adds its own header and, in the case of Data Link protocols, trailer control information to the basic data structure and encapsulates the protocol data unit (PDU) from the layer

above. On the receiving end, this header and trailer information is stripped, one layer at a time, until the equivalent of the original data arrives at its final destination.

Note:

PDU is a generic term used to describe the end product of a protocol. It can be thought of as the entire data structure handed down by that protocol to the protocol at the next lowest layer, or the information placed on the network media by the Physical layer. A PDU will consist of the original user data and any upper-layer control information (headers and trailers) imposed by upper-layer protocols encapsulated by the control information of the protocol creating the PDU.

Now let’s look at how TCP and IP work together.

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TCP/IP Design Goals

TCP/IP Design Goals
When the U.S. Department of Defense began to define the TCP/IP network protocols, their design goals included the following:

•       TCP/IP had to be independent of all hardware and software manufacturers. Even today, this is fundamentally why TCP/IP makes such good sense in the corporate world: It is not tied to IBM, Novell, Microsoft, DEC, or any other specific company.
•     It had to have good built-in failure recovery. Because TCP/IP was originally a military proposal, the protocol had to be able to continue operating even if large parts of the network suddenly disappeared from view, say, after an enemy attack.
•        It had to handle high error rates and still provide completely reliable end-to-end service.  It had to be efficient and have a low data overhead. The majority of IP packets have a simple, 20-byte header, which means better performance in comparison with other networks. A simple protocol translates directly into faster transmissions, giving more efficient service.  It had to allow the addition of new networks without any service disruptions.

        As a result, TCP/IP was developed with each component performing unique and vital functions that allowed all the problems involved in moving data between machines over networks

to be solved in an elegant and efficient way. Before looking at both TCP and IP individually, you should understand where TCP/IP fits into the broader world of network protocols and, particularly,

how it compares to the theoretical reference model published by the International Organization for Standardization (ISO) as the OSI model.

     The popularity that the TCP/IP family of protocols enjoys today did not arise just because the protocols were there, or even because the U.S. government mandated their use. They are popular because they are robust, solid protocols that solve many of the most difficult networking problems and do so in an elegant and efficient way.

The Internet, an internet, an intranet, and an extranet
The title of this sidebar may be a bit confusing and look a bit informal with the odd capitalization, but it’s for a very good reason. While internet is a truncated version of internetwork, a lot of play has come from the root of these words. Let’s examine the word internetwork first, just to make sure we understand where all the variants come from. As you know, a network is a conglomeration
of devices tied together with a common technology. Well, once you establish two or more of these networks, work can be started on bringing them together. The interconnection and intercommunication between these autonomous networks is known as an internetwork or just internet. We know we have an internet when we use routers or other layer 3 devices to interconnect the networks. What kind of fun can we have with these words?

First of all, just by capitalizing the word internet to form Internet, we get the proper name of the global commercial internetwork that is tied together by TCP/IP (actually, all of these entities are)
and that has a scope of the planet we call home. If those Mars rovers have IP addresses, the scope suddenly gets a bit grander. That’s the flexibility of TCP/IP for you. What if we analyze the
meaning of inter? An internet is connectivity and communication across network boundaries. Does that mean, then, that an intranet is connectivity and communication within a network?
Gotcha. An intranet is more an opposite of the Internet, in terms of scope. If the Internet spans many administrative boundaries, encompassing many disparate networks, then an intranet,
while often an internet (how’s that for a catch?), encompasses only networks under a single administrative domain, a large corporation’s internal internetwork. Did you catch that? An intranet can be an internet, but not the Internet. Fun, huh?
Well, then, that just leaves extranet. Think of an extranet as an intranet becoming a very controlled Internet. That is, if an intranet is made up of all networks under a single administrative control, then an extranet is the expansion of that to include one, two, or just a few additional outside networks. Said differently, an extranet is an intranet interconnected and intercommunicating with networks that are under separate administrative control. This isn’t nearly as
unruly as the Internet, because this interconnectivity arose from some sort of partnership or affiliation between the parties. Let’s say, for instance, that a manufacturing company wants to have a vendor monitor its inventory so that whenever materials that the vendor supplies reach a minimum threshold, an order can be generated automatically, without personnel from the manufacturing company getting involved. That would require some sort of limited vendor access to internal manufacturing company resources. While the manufacturing company wants the vendor to have access to all that they need to help automate the supply process, they don’t want the vendor accessing sensitive financial, personnel, or possibly engineering information. By tweaking the firewalls just so, the vendor’s trusted network assets can be allowed access to the manufacturing company’s inventory control system but nothing else. That’s an extranet. While there’s a big difference between them all, they are all very similar. They are all generally TCP/IP internetworks.

Benefits of Using TCP/IP over Other Networking Protocols
   There are several benefits to using the TCP/IP networking protocol:

•     TCP/IP is a widely published open standard and is completely independent of any hardware or software manufacturer.
•     TCP/IP can send data between different computer systems running completely different operating systems, from small PCs all the way to mainframes and everything in between.
•     TCP/IP is separated from the underlying hardware and will run over Ethernet, Token Ring, and X.25 networks, to name a few, and even over dial-up telephone lines.
•     TCP/IP is a routable protocol, which means it can send datagrams over a specific route, thus reducing traffic on other parts of the network.
•     TCP/IP has reliable and efficient data-delivery mechanisms.
•     TCP/IP uses a common addressing scheme. Therefore, any system can address any other system, even in a network as large as the Internet. (We will look at this addressing scheme in the section “Understanding IP Addressing” later in this chapter.)

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A Brief History of TCP/IP

A Brief History of TCP/IP
The first Request for Comments (RFC) was published in April 1969, laying the groundwork for today’s Internet, the protocols of which are specified in the numerous RFCs monitored,
ratified, and archived by the Internet Engineering Task Force (IETF). TCP/IP was first proposed in 1973 and was split into separate protocols, TCP and IP, in 1978. In 1983, TCP/IP
became the official transport mechanism for all connections to ARPAnet, a forerunner of the Internet, replacing the earlier Network Control Protocol (NCP). ARPAnet was developed by
the Department of Defense’s (DoD’s) Advanced Research Projects Agency (ARPA), formed in 1957 in response to the Soviet Union’s launch of Sputnik and later renamed the Defense Advanced Research Projects Agency (DARPA), which was split into ARPAnet and MILNET in 1983 and disbanded in 1990.
Much of the original work on TCP/IP was done at the University of California, Berkeley, where computer scientists were also working on the Berkeley version of UNIX (which eventually grew into the Berkeley Software Distribution [BSD] series of UNIX releases). TCP/IP was added to the BSD releases, which in turn was made available to universities and other institutions for the cost of a distribution tape. Thus, TCP/IP began to spread in the academic world, laying the foundation for today’s explosive growth of the Internet and of intranets as well.
      During this time, the TCP/IP family continued to evolve and add new members. One of the most important aspects of this growth was the continuing development of the certification and
testing program carried out by the U.S. government to ensure that the published standards, which were free, were met. Publication ensured that the developers did not change anything or
add any features specific to their own needs. This open approach has continued to the present day; use of the TCP/IP family of protocols virtually guarantees a trouble-free connection

between many hardware and software platforms.

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Introducing TCP/IP

Introducing TCP/IP

Because TCP/IP is so central to working with the Internet and with intranets, you should understand it in detail. We’ll start with some background on TCP/IP and how it came about and then move on
to the descriptions of the technical goals defined by the original designers. Then you’ll get a look at how TCP/IP compares to a theoretical model, the Open Systems Interconnect (OSI) model.

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Design Hotspot-50 Server Mikrotik

Design Hotspot-50  Server Mikrotik

حمل من هنا 

رجاء تغيير بيانات الاتصال 

مع تحيات كنزى نت

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TCP/IP Fundamentals Network+ Chapter 3

Network+™  

"Quoting one of e-books"

Chapter 3 :

           TCP/IP Fundamentals

                Introducing TCP/IP 

                    A Brief History of TCP/IP 

                     TCP/IP Design Goals 

                    TCP/IP and the OSI Model 

                The Transmission Control Protocol 

                The Internet Layer Protocols 

                     The Internet Protocol 

                     Internet Control Message Protocol (ICMP) 

                     Address Resolution Protocol (ARP) and

                         Reverse ARP (RARP) 

                     Routers and Routing 

                 The Application Protocols 

                    Simple Network Management Protocol (SNMP) 

                    File Transfer Protocol (FTP) 

                    Trivial File Transfer Protocol (TFTP) 

                    Secure File Transfer Protocol (SFTP) 

                    Simple Mail Transfer Protocol (SMTP) 

                    Post Office Protocol (POP) 

                    Internet Message Access Protocol, Version 4 (IMAP4)

                    Line Printer Daemon (LPD) 

                    Network File System (NFS) 

                    Telnet 

                    Secure Shell (SSH) 

                    Hypertext Transfer Protocol (HTTP) 

                    Hypertext Transfer Protocol Secure (HTTPS) 

                       Contents

                    Network Time Protocol (NTP) 

                    Network News Transfer Protocol (NNTP) 

                    Secure Copy Protocol (SCP) 

                    Lightweight Directory Access Protocol (LDAP) 

                    Internet Group Management Protocol (IGMP) 

                    Line Printer Remote (LPR) 

                 Other Upper-Layer Protocols 

                    User Datagram Protocol (UDP) 

                    Server Message Block (SMB) 

                    AppleTalk Filing Protocol (AFP) 

                    Internet Connection Sharing (ICS) 

                Overview of Ports and Sockets 

                Understanding IP Addressing 

                    Overview of Ethernet Addresses 

                    Overview of IP Addresses 

                    Understanding Subnets 

                    Subnetting a Class C Network 

                    Classless Inter-Domain Routing (CIDR) 

                     IP Proxy Servers

                 Name Resolution Methods 

                    Internet Domain Organization 

                    Using HOSTS 

                    Using DNS 

                    Using WINS 

                 Configuring TCP/IP on Windows Workstations 

                    The IP Settings Tab 

                    The DNS Tab 

                    The WINS Tab 

                    The Options Tab 

                    The Windows Registry 

                    Zero Configuration (ZeroConf) 

                Virtual LANs (VLANs) 

                    Summary 

                    Exam Essentials 

                    Review Questions 

                    Answers to Review Questions

*************

"Quoting one of e-books"

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Review Questions ( Network+ Chapter 2 )

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.

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Answers to Review Questions ( Network+ Chapter 2 )

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.

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Exam Essentials ( Network+ Chapter 2 )

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.

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AppleTalk and AppleTalk over IP

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.

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