Clock Rates DCE and DTE

When a network engineer needs to add a point-to-point leased line between two routers, he contacts a service provider and orders the circuit. As part of that process, the customer specifies how fast the circuit should run, in kilobits per second (kbps). While the circuit is being set up by the telco, the engineer purchases two CSU DSUs, installs one at each site, and configures each CSU DSU. He also cables each router to the respective CSU DSU using the cables shown in the previous section....

OSI Layer 1 for Pointto Point WANs

The OSI physical layer, or Layer 1, defines the details of how to move data from one device to another. In fact, many people think of OSI Layer 1 as sending bits. Higher layers encapsulate the data, as described in Chapter 2, The TCP IP and OSI Networking Models. No matter what the other OSI layers do, eventually the sender of the data needs to actually transmit the bits to another device. The OSI physical layer defines the standards and protocols used to create the physical network and to send...

OSI Networking Models

The term networking model, or networking architecture, refers to an organized description of all the functions needed for useful communications to occur. Individual protocols and hardware specifications then are used to implement the functions described in the networking model. When multiple computers and other networking devices implement these protocols, which, in turn, implement the functions described by the networking model, the computers can successfully communicate. You can think of a...

Comparison of Remote Access Technologies

This chapter scratches the surface of how modems, ISDN, cable, and DSL work. Consumers choose between these options for Internet access all the time, and network engineers choose between these options for supporting their work-at-home users as well. So, it seems appropriate to close the chapter by listing some of the key comparison points for these options. Comparison of Remote Access Technologies 465 The remote access technologies in this chapter provide services at Layer 1, and possibly Layer...

Do I Know This Already Quiz

In which of the following modes of the CLI could you configure the duplex setting for interface fastethernet 0 5 Answer E. The duplex command is an interface subcommand. 2. In which of the following modes of the CLI could you issue a command to erase the initial configuration of the switch Answer B. The erase command is an exec command, so it cannot be issued from any configuration mode. User mode does not allow the use of the erase command. 3. What type of switch memory is used to store the...

Identifying the Data Inside an Ethernet Frame

Each data-link header has a field in its header with a code that defines the type of protocol header that follows. For example, in the first frame in Figure 3-13, the Destination Service Access Point (DSAP) field has a value of E0, which means that the next header is a Novell IPX header. Why is that Well, when the IEEE created 802.2, it saw the need for a protocol type field that identified what was inside the field called data in an IEEE Ethernet frame. Figure 3-13 802.2 SAP and SNAP Type...

What Subnet Masks Meet the Stated Design Requirements

So far in this chapter, the text has explained how to answer questions that provide the subnet number. However, some questions do not supply the subnet number, but instead ask you to choose the correct subnet mask, given a set of requirements. The most common of these questions reads something like this You are using Class B network X, and you need to have 200 subnets, with at most 200 hosts per subnet. Which of the following subnet masks can be used (followed by some subnet masks that you can...

Whats on the CCNA Exams

Ever since I was in grade school, whenever the teacher announced that we were having a test soon, someone would always ask, What's on the test Even in college, people would try to get more infomrmation about what would be on the exams. At heart, the goal is to know what to study hard, what to study a little, and what to not study at all. Cisco does want you to know what topics to study and wants you to be well prepared for your exams. However, Cisco does not want to be so specific that you...

OSI Layers

The OSI reference model consists of seven layers. Each layer defines a set of typical networking functions. When OSI was in active development in the 1980s and 1990s, the OSI committees created new protocols and specifications to implement the functions specified by each layer. In other cases, the OSI committees did not create new protocols or standards, but instead referenced other protocols that were already defined. For instance, the IEEE defines Ethernet standards, so the OSI committees did...

Network Topologies

You already have been introduced to several different network topologies as you have read through this book. For instance, 10BASE2 networks use a physical bus topology, whereas 10BASE-T networks use a physical star topology. This section introduces you to several other types of network topologies. Figure 11-1 shows the different types of Ethernet topologies covered earlier in the book, with some specific terms used to describe the topology for each design. Figure 11-1 Different Types of Network...

Modulation and Demodulation

Most people can fully appreciate the concept of the speed of a dialed circuit in terms of bits per second. However, another term, baud, often is used to describe the speed of a modem. In fact, some people say things like That modem runs at 33 kilo baud per second, really meaning 33 kilobits per second (kbps), thinking that bits per second and baud per second are the same thing. But the two terms are not synonymous, as you will read shortly. Modems create an analog signal when sending data. As...

CCNA Exam Topics

Interestingly, the CCNA (640-801) exam topics posted by Cisco are not simply the combination of the INTRO exam topics and the ICND exam topics. If you look closely, the CCNA exam topics match more closely to the ICND exam topics than they do to the INTRO exam topics. So, for those of you planning to take the single CCNA exam, what does that mean Well, for practical purposes, the CCNA exam covers all the topics covered on both the INTRO and ICND exams. However, the length of the CCNA exam does...

Classes of Networks

In Figure 5-3 and the surrounding text, I claimed that the IP addresses of devices attached to the Token Ring all started with 8 and that the IP addresses of devices attached to the Ethernet all started with 130.4. Why only one number for the prefix on the Token Ring and two numbers on the Ethernet Well, it all has to do with IP address classes. RFC 790 defines the IP protocol, including multiple different classes of networks. IP defines three different network classes, called A, B, and C, from...

Network Layer Layer 3 Addressing

One key feature of network layer addresses is that they were designed to allow logical grouping of addresses. In other words, something about the numeric value of an address implies a group or set of addresses, all of which are considered to be in the same grouping. In TCP IP, this group is called a network or a subnet. In IPX, it is called a network. In AppleTalk, the grouping is called a cable range. These groupings work just like U.S.P.S. ZIP codes, allowing the routers (mail sorters) to...

Layer 1 and Layer 2 between the Home and the Head

Cable TV systems originally were built to send TV video and audio signals to lots of places, with no need to receive a signal back. In other words, the idea of having someone's TV send some information back to the cable company was not even under consideration. Because the original CATV architecture allowed for sending signals from the head end outward, and the capability for two-way communication was added later, data over cable standards treats data going toward the home differently than data...

Bandwidth Clock Rate and Serial Lines in the

As mentioned back in Chapter 4, Fundamentals of WANs, you can build a WAN link in a lab without using a CSU DSU. The lab network that I used to build the examples in this chapter used three back-to-back serial cables, essentially a DTE and DCE cable pair connected together. To use a back-to-back WAN connection, one router must supply the clocking. Example 13-7 shows an example configuration for Seville, with a couple of important commands related to WAN links. Example 13-7 Seville Router...

The Flintstones Network The First Computer Network

The Flintstones are a cartoon family that, according to the cartoon, lived in prehistoric times. Because I want to discuss the thought process behind some imaginary initial networking standards, the Flintstones seem to be the right group of people to put in the example. Fred is the president of FredCo, where his wife (Wilma), buddy (Barney), and buddy's wife (Betty) all work. They all have phones and computers, but they have no network because no one has ever made up the idea of a network...

Internet Control Message Protocol

Earlier in this chapter, you read about how to configure IP addresses and how to perform some basic troubleshooting. For troubleshooting, you have seen how to look at the routing table with the show ip route command, how to look at interface status with several options on the show interfaces command, and how to use standard and extended ping commands for basic troubleshooting. TCP IP includes a protocol specifically to help manage and control the operation of a TCP IP network, called the...

LAN Segmentation

Network Segmentation

LAN segmentation simply means breaking one LAN into parts, with each part called a segment. The term LAN segment comes from the original use of a physical bus with 10BASE2 and 10BASE5. A single Ethernet segment consisted of the devices connected serially with coaxial cable. When 10BASE-T came along, the term segment still was used, this time to identify a hub with multiple devices connected to it. Figure 9-7 repeats an earlier figure, but with the term segment noted on the figure. Figure 9-7...

WAN Cabling Standards

Cisco offers a large variety of different WAN interface cards for its routers, including synchronous and asynchronous serial interfaces. For any of the point-to-point serial links or Frame Relay links in this chapter, the router uses an interface that supports synchronous communication. Synchronous serial interfaces in Cisco routers use a variety of proprietary physcial connector types, such as the 60-pin D-shell connector shown in Figure 4-4. The cable connecting the router to the CSU uses a...

Example Configuration Process

Example 7-1 illustrates how the console password is defined gives host name, prompt, and interface descriptions and shows the finished configuration. The lines beginning with are comment lines that highlight significant processes or command lines within the example. The show running-config command output also includes comment lines with just a to make the output more readable many comment lines in the examples in this book were added to explain the meaning of the configuration. You should...

Telnet and Suspend

The telnet IOS exec command enables you to Telnet from one Cisco device to another in practical use, it is typically to another Cisco device. One of the most important features of the telnet command is the suspend feature. To understand the suspend function, you should to refer to the network diagram in Figure 13-4. In the figure, the router administrator is using Bench to Telnet into the Cincy router. When in Cincy, the user Telnets to Milwaukee. When in Milwaukee, the user suspends the Telnet...

Introduction to Computer Networking Concepts

This chapter gives you a light-hearted perspective about networks, how they were originally created, and why networks work the way they do. Although no specific fact from this chapter happens to be on either of the CCNA exams, this chapter helps you prepare for the depth of topics you will start to read about in Chapter 2, The TCP IP and OSI Networking Models. If you are brand new to networking, this short introductory chapter will help you get ready for the details to follow. If you already...

Link Speeds Offered by Telcos

No mater what you call them telcos, PTTs, service providers these companies do not simply let you pick the exact speed of a WAN link. Instead, standards define how fast a point-to-point link can run. For a long time, the telcos of the world made more money selling voice services. That is no longer the case for any of these companies in the United States, except for the companies that provide local residential telephone service. So, years ago, the telcos of the world developed a standard for...

Foundation Summary

The Foundation Summary section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your CCNA exam, a well-prepared CCNA candidate should know, at a minimum, all the details in each Foundation Summary section before going to take the exam. Figure 4-12 depicts some of those key concepts and terms used with point-to-point WAN leased lines. Figure 4-12 Point-to-Point Leased Line Components and Terminology -...

What Is the Subnet Number and What Are the IP Addresses in the Subnet

One of the most common things you need to figure out is that after you know an IP address and subnet mask, you must answer questions about them. The question might be straightforward, such as What is the subnet number , or it might be more subtle, such as Which of the following IP addresses are in the same subnet as the stated address In either case, if you can dissect an IP address as described in this chapter, you can answer any variation of this type of question. In the next several...

The CCNA Certification Exams What Theres More than One Exam

For the first time since Cisco announced CCNA in 1998, the CCNA certification has an option for multiple exams. Before Cisco announced these latest changes around summer of 2003, to get your CCNA certification, you just passed a single CCNA exam. With this latest generation of the CCNA, you can either take a single exam to get your CCNA, or you can take two exams, with each of these exams covering a subset of the CCNA exam topics. Table I-1 lists the exams. Table I-1 CCNA Exam Names and Numbers...

How Many Hosts and How Many Subnets

You also should know how to figure out how many network, subnet, and host bits are used with that subnetting scheme. From those facts, you easily can figure out how many hosts exist in the subnet and how many subnets you can create in that network using that subnet mask. You already have learned that Class A, B, and C networks have either 8, 16, or 24 bits in their network fields, respectively. Those rules do not change. You also already have read that, without subnetting, Class A, B, and C...

Data Encapsulation

The term encapsulation describes the process of putting headers and trailers around some data. A computer that needs to send data encapsulates the data in headers of the correct format so that the receiving computer will know how to interpret the received data. You have seen several examples of encapsulation in this chapter already. The web server encapsulated the home page inside an HTTP header in Figure 2-2. The TCP layer encapsulated the HTTP headers and data inside a TCP header in Figure...

About the Ccna Intro Exam Certification Guide and Ccna Icnd Exam Certification Guide

As mentioned earlier in this introduction, you can take both the INTRO and ICND exams to acquire CCNA certification, or you can take a single CCNA exam. Because of the significantly expanded topics as compared with the previous CCNA exam, there was simply too much material for a single book. So, we simply created two books one for the INTRO exam and one for the ICND exam. The contents of the two books, however, were actually designed for both the single-exam and dual-exam audience. For those of...

Operating Cisco LAN Switches

Cisco's LAN switch revenue surpassed router revenues about the time that the CCNA certification was first announced back in 1998, so there is little doubt about the importance of LAN switches to Cisco. Also, the vast majority of end-user devices connect to a network by connecting to a LAN switch. So, it's no surprise that the CCNA certification exams cover switching concepts extensively. Cisco uses two major alternatives for LAN switch operating systems. Also, each model series of switches from...

Math Operations Used to Answer Subnetting Questions

Computers, especially routers, do not think about IP addresses in terms of the conventions shown in Table 12-2. They think in terms of 32-bit binary numbers, which is fine because, technically, that's what IP addresses really are. Also, computers use a mask to define the structure of these binary IP addresses. A full understanding of what that means is not too difficult. However, getting accustomed to doing the binary math in your head is challenging for most of us, particularly if you don't do...

How to Use These Books to Prepare for the CCNA Exam

If you are using this book to study for the INTRO exam, just follow the plan outlined in the last few pages. However, to use this book to study for the CCNA exam, you really should use both this book and the CCNA ICND Exam Certification Guide. (By the way, if you've not bought this book yet and you want both, you can generally get the pair cheaper by buying a set, called the CCNA Certification Library.) These two books were designed to be used together to help those who want to get their CCNA...

Format of the CCNA Exams

The INTRO, ICND, and CCNA exams all follow the same general format. When you get to the testing center and check in, the proctor will give you some general instructions and then take you into a quiet room with a PC. When you're at the PC, you have a few things to do before the timer starts on your exam for instance, you can take a sample quiz, just to get accustomed to the PC and to the testing engine. Anyone who has user-level skills in getting around a PC will have no problems with the...