CHAPTER 6: The OSI Model and Networking Protocols 276 layers for standard, reliable network communications: physical, data link, network, transport, session, presentation, and application. The acronym commonly used to remember this is (in reverse order): all people seem to need data processing. If you were to follow each layer and map to it a protocol and a device, then by reading this chapter, you would remember that the physical layer is responsible for signaling, transmission medium, and 1s and 0s travers- ing the wire. As we move up the model, things get increasingly more com- plex. The next layer, the data link layer, is where your MAC address is located. We discussed the functionality of a NIC card and what a MAC address is. On Ethernet NICs, the physical or MAC address (also called the hardware address) is expressed as 12 hexadecimal digits, arranged in pairs with colons between each pair, for example, 12:3A:4D:66:3A:1C. In binary notation, this translates to a 48-bit (or 6-byte) number, with the initial 3 bytes representing the manufacturer and the last 3 bits representing a unique NIC made by that manufacturer. The data link layer is subdivided into two sublayers, known as the LLC and MAC layer. The LLC sublayer is responsible for providing the logic for the data link, and thus it controls the synchronization, flow control, and error checking functions of the data link layer. The TCP/IP protocol suite provides the functionality specified in the OSI model using the four related layers of the DoD model: Network Interface, Internet, Host-to-Host, and Application. The Network Interface maps to the physical and data link layers, and the Internet layer maps to the OSI net- work layer. The Host-to-Host layer maps to the transport layer and DoD’s application layer maps to the session, presentation, and application layers of the OSI model. Some of the more commonly known application layer pro- tocols are FTP, HTTP, POP3, WINS, DNS, and DHCP. Understanding the details of the TCP/IP protocol suite is fundamental to managing computers in today’s networked environment. Being able to subnet, assign IP addresses, create subnet masks, and set up routing are essential skills you’ll need on the job and to successfully master the material on the Network exam. In our next chapter, we get more intimate with the TCP/IP suite. EXAM OBJECTIVES FAST TRACK The OSI Model The OSI model has seven defined layers. The seven layers of the OSI model are physical, data link, network,  transport, session, presentation, and application. Exam Objectives Fast Track 277 An acronym commonly used to remember the seven layers is  All People Seem To Need Data Processing. Each layer of the OSI model is responsible for a specific set of  network communication functions. The IEEE 802.3 standard was originally developed by Xerox. It was  eventually standardized as the IEEE 802.3 based on the Ethernet DIX standard. The DIX standard comprised of companies who originally created the specification, which are Digital, Intel, and Xerox, hence DIX. The IEEE 802.3 standard covers all Ethernet-based networks such  as 10 megabits per second (Mbps), 100 Mbps, and 1000 Mbps networks. One thing to consider is that Ethernet is not Fast Ethernet; they are different standards, so they rate different subcommittees. For example, Ethernet Encapsulation Standards/Ethernet (802.3), Fast Ethernet (802.3u), Gigabit Ethernet (802.3z), and Gigabit Ether- net over copper (802.3ab), but they are all primarily 802.3. In 1995, the IEEE defined the 802.3u Fast Ethernet standard  (100BaseTX, 100BaseT4, 100BaseFX). Hubs operate at the physical layer of the OSI model. Switches operate at the data link layer of the OSI model. Bridges operate at the data link layer of the OSI model. Routers operate at the network layer of the OSI model. NICs operate at the data link layer of the OSI model. APs operate at the data link layer of the OSI model. The DoD Network Model The DoD model was originally designed to share computer data  across a wide area between several large, mainframe computers. The DoD’s Advanced Research Projects Agency (DARPA) formed an  internetworking experiment called ARPANet. The DoD model used four layers: Network Interface, Internet,  Host-to-Host, and Application. The  Network Interface layer of the DoD model corresponds to Layers 1 and 2 in the OSI model. CHAPTER 6: The OSI Model and Networking Protocols 278 The  Internet layer maps to the network layer of the OSI model. The Internet layer is responsible for packaging, addressing, and routing the data. The  Host-to-Host Transport layer maps to the transport layer (Layer 4) in the OSI model. The  Application layer maps to the session, presentation, and application layers of the OSI model. Networking Protocols NetBT is an application layer set of protocols that provides  name, session, and datagram services for NetBIOS applications. Name service uses UDP Port 137, datagram service uses UDP Port 138, and the session service uses TCP Port 139. WINS is a NetBIOS name server that NetBIOS clients can use to  attain, register, and resolve NetBIOS names. WINS is used in the legacy Microsoft networks. Server Message Block (SMB) protocol is primarily used for file and  print sharing in earlier versions of Windows operating system. IPP provides the capability to perform various printing operations  across the network and Internet. WinSock is a Microsoft Windows  API that provides a standard programming interface for accessing TCP/IP in Windows. Telnet is a terminal emulation protocol that allows you to log  onto a remote computer. To do this, telnet services should be running on the server. Telnet uses port 23 (both TCP and UDP) for communication. SSH, which is a secure terminal emulation, runs on 22 (both TCP and UDP). DHCP, which is used to automatically (or dynamically) assign IP  addresses to host computers on a network running TCP/IP. You have the DHCP servers that issue IP addresses and DHCP clients that request for IP addresses in a DHCP environment. The SMTP is a protocol used to transfer e-mail messages  and attachments. SMTP is used to transmit e-mail between e-mail servers and from e-mail clients. SMTP uses port 25 for communication. Exam Objectives Frequently Asked Questions 279 POP is a widely used e-mail application protocol that can be used  to retrieve e-mail from an e-mail server for the client applications. POP3 uses port 110 for communication. IMAP is similar to Webmail in which mails reside in the server and  the clients use a Web-based interface to access their mails. IMAP4 uses Port 143. HTTP is the protocol used to transfer files used on the Internet to  display Web pages. HTTP uses port 80 for communication. HTTPS, which is basically secure HTTP, uses SSL to encrypt Web traffic running. SSL runs on port 443. DNS is used to resolve a hostname to an IP address to facilitate the  delivery of network data packets. DNS uses port 53 for communication. The following is a quick summary of commonly used applications  and ports: Port 20 maps to FTP Port 21 maps to FTP Port 22 maps to SSH Port 23 maps to Telnet Port 25 maps to SMTP Port 53 maps to DNS Port 80 maps to HTTP Port 110 maps to POP3 Port 119 maps to NNTP Port 123 maps to NTP Port 143 maps to IMAP4 Port 443 maps to HTTPS Port 137 (UDP) maps to the name service Port 133 (UDP) maps to the datagram service Port 139 (TCP) maps to the session service EXAM OBJECTIVES FREQUENTLY ASKED QUESTIONS How exactly does the Network Interface layer of the DoD model Q: map to the physical and data link layers of the OSI model? The DoD’s Network Interface layer maps directly to the physical A: and data link layers of the OSI model, with one notable exception. CHAPTER 6: The OSI Model and Networking Protocols 280 There are two parts to the data link layer: the LLC and the MAC sublayers. TCP/IP does not implement the LLC element at the Network Interface layer. This function is handled further up the protocol stack at the Host-to-Host (Transport) layer. How likely am I to see a question related to the DoD DARPA Q: model or ARPANet on the exam? It’s unusual to see a question directly related to these topics, but A: you will see questions that rely upon your understanding of both the OSI model and the TCP/IP suite. Understanding the origins of these models will help you answer questions related to the networking models. Isn’t ARPANet the same thing as the Internet? Why do I need to Q: know this anyway? ARPANet was the first working implementation of internet-A: working. The structures devised in the experiment as well as the knowledge gained during that project form the foundation of the Internet. The ARPANet was a network of a few mainframe computers and was neither universally available, as the Internet is today, nor a commercial network (all nodes were located at uni- versities or government agencies). It is possible that you’ll see an exam question that uses ARPANet as an answer. Understanding the origins of the Internet can help you answer other questions on the exam, sometimes by simply helping you eliminate wrong answers. There are a lot of application layer protocols in the TCP/IP suite. Q: Am I expected to memorize them all? There is an ever-expanding set of application layer protocols in A: use today. It’s important to get a firm understanding of the most common protocols and to have at least a familiarity with the less common protocols. At the very least, you should be very familiar with NetBT, DNS, DHCP, WINS, Telnet, SMTP, HTTP, FTP, RIP, and SNMP. SELF TEST Which OSI model layer is responsible for frame sequencing?1. A. The physical layer B. The transport layer Self Test 281 C. The data link layer D. The application layer You are a network technician assigned to install a new network 2. hub. Which layer of the OSI model does a standard hub operate at? Select only one answer. A. Physical layer B. Data link layer C. Network layer D. Transport layer You are a network technician assigned to install a new network 3. switch. Which layer of the OSI model does a standard switch (or bridge) operate at? Select only one answer. A. Physical layer B. Data link layer C. Network layer D. Transport layer You are a network technician assigned to install a new network 4. Router. Which layer of the OSI model does a standard router operate at? Choose all that apply. A. Physical layer B. Data link layer C. Network layer D. Transport layer You are a network technician assigned to install a new NIC in a 5. PC. Which layer of the OSI model does a NIC operate at? Select only one answer. A. Physical layer B. Data link layer C. Network layer D. Transport layer What is the unique physical address (Burned in Address [BIA]) that 6. is found on all NICs called? A. DNS address B. NAT address CHAPTER 6: The OSI Model and Networking Protocols 282 C. IP address D. MAC address Which of the following is a valid MAC address?7. A. 00:05:J6:0D:91:K1 B. 10.0.0.1-255.255.255.0 C. 00:05:J6:0D:91:B1 D. 00:D0:A0:5C:C1:B5 You are the system administrator for a small company that runs 8. two Windows servers (Windows Server 2003) and two Linux servers (SUSE Linux). You need to lock down the connections to the switch via port security; this essentially means you will need to retrieve the MAC addresses on the systems. MAC addresses are found on Linux server by issuing which command? A. ipconfig /a B. ifconfig /a C. winipcfg /a D. ifconfig –a From the list of choices, which of the following media access 9. methods is used for an IEEE 802.5 network? A. Direct sequence B. Token passing C. CSMA/CD D. CSMA/CA Which of the following provides NetBIOS name to IP address 10. resolution? A. Hosts B. lmhosts C. Services D. Protocols POP3 is identified by which TCP/IP port number?11. A. UDP Port 21 B. TCP Port 23 Self Test 283 C. UDP Port 25 D. TCP Port 110 Standards for CSMA/CD are specified by which IEEE 802 12. sublayer? A. 802.1 B. 802.2 C. 802.3 D. 802.5 From the choices listed, which of the following protocols represents 13. e-mail protocols? Please choose two from the list below. A. POP3 B. SMNP C. IMAP4 D. Telnet When discussing the OSI model and the DoD model, which layers 14. of the OSI model handle what you would find in the Application layer of the DoD model? Choose all that apply. A. Application B. Presentation C. Transport D. Session You are a network administrator looking to implement technol-15. ogy into a company. You are told you need to build a network using the IEEE 802.11 standard. From the list below, the IEEE 802.11 standard maps to which of the following? Select only one answer. A. Token Ring B. Wired Ethernet C. Metropolitan Area Network (MAN) D. Wireless in Infrastructure mode CHAPTER 6: The OSI Model and Networking Protocols 284 SELF TEST QUICK ANSWER KEY C1. A2. B3. C4. B5. D6. D7. D8. B9. B10. D11. C12. A and C13. A, B, and D14. D15. 285 CHAPTER 7 EXAM OBJECTIVES IN THIS CHAPTER TCP/IP 286 IPv4 287 IPv6 289 UNDERSTANDING IP ADDRESSING 294 UNDERSTANDING SUBNETTING 305 STRATEGIES TO CONSERVE ADDRESSES 320 PRIVATE NETWORK ADDRESSES 322 MULTICAST, BROADCAST, AND UNICAST 329 UNDERSTANDING BASIC IP ROUTING 335 INTRODUCTION Transmission Control Protocol/Internet Protocol (TCP/IP) is a term we recog- nize easily due to its ever-increasing function in connecting our computers to the Internet. TCP/IP is a network protocol used to provide the logical commu- nication structure needed to send and receive data on a computer network. This logical communication structure is the complicated part, and what we will be primarily learning about in this chapter. The Network exam calls for an understanding of routable and routing protocols in terms of routing, addressing schemes, interoperability, and naming conventions. This chapter, as well as sections of the next chapter, will cover many aspects of TCP/IP, especially those areas made testable by the Network posted objectives. This chapter’s main focus will be on TCP/IP. The reasoning for this is simple; not only is TCP/IP one of the most thoroughly tested knowledge areas on the exam, but it is also the most widely used and integrated proto- col in use today around the world. Not knowing TCP/IP can be somewhat TCP/IP and Routing . with one notable exception. CHAPTER 6: The OSI Model and Networking Protocols 280 There are two parts to the data link layer: the LLC and the MAC sublayers. TCP/IP does not implement the LLC. THIS CHAPTER TCP/IP 286 IPv4 287 IPv6 289 UNDERSTANDING IP ADDRESSING 294 UNDERSTANDING SUBNETTING 305 STRATEGIES TO CONSERVE ADDRESSES 320 PRIVATE NETWORK ADDRESSES 322 MULTICAST, BROADCAST, AND. and receive data on a computer network. This logical communication structure is the complicated part, and what we will be primarily learning about in this chapter. The Network exam calls for