Final Lab Scenario

The current CCNA exams include simulated lab questions. The best way to prepare for those is to work with live networks using Cisco routers and switches. You should also make sure to do all the questions in the testing engine on the CD, as it contains a large number of simulated lab questions. You can also use the NetSim network simulator on the CD, or rent time via online labs. Regardless of how much time and effort you spend with hands-on practice, the following lab scenario can help you with...

Accessing Net Sim from the CD

Accessing NetSim from the CD is relatively simple. Put the CD in the CD drive, and the software on the CD starts. (If it doesn't, run the command autorun.exe that is on the CD's root directory.) After logging in, select the Hands-on Practice Exercises and NetSim Demo Software link in the main menu. Another menu opens that allows you to view the CD-only appendixes of labs and to start the NetSim software. NetSim lets you pick which lab topology to load. You pick a lab topology, and you next see...

Accessing the Cisco 2950 Switch CLI

The 2950 CLI works just like the router IOS CLI. Some of the commands you use are different because switches perform different tasks than routers, but the process and the look and feel are the same. For instance It uses user exec and priviledged (enable) exec modes. It uses the enable and disable commands to move between the two. It uses a console password and telnet (vty) password, configured just like a router. It uses an enable secret or just plain enable password, with the enable secret...

Acknowledgments

The technical editing team for this book and its companion volume was fantastic Not only did they find where I had simply written the wrong technical facts, but they also helped me find new, more interesting, and clearer ways to convey certain facts about networking. Lynn was particular helpful with comments that helped keep small sections in line with the overall theme of the chapter a skill I'm sure he developed as a result of having written books himself. Martin helped a lot with technical...

Address Resolution Protocol and the Domain Name System

Network designers should try to make using the network as simple as possible. At most, users might want to remember the name of another computer with which they want to communicate, such as remembering the name of a web site. They certainly do not want to remember the IP address, nor do they want to try to remember any MAC addresses So, TCP IP needs to have protocols that dynamically discover all the necessary information to allow communications, without the user knowing more than a name. You...

Analog Modem Summary

Modems have the great advantage of being the most pervasively available remote access technology. The history of modems is long, with modems growing to be a very reliable choice for remote access. Speeds have improved over the years, with compression technology increasing the effective throughput to beyond 100 kbps. Modems provide a Layer 1 service of delivering a bit stream between the two endpoints on the dialed circuit. To pass IP traffic, an appropriate data-link protocol must be used,...

Analog Modems

Analog modems allow two computers to send and receive a serial stream of bits, with no physical changes required on the typical analog local loop between a residence and the telco CO. Because the switch in the CO expects to send and receive analog voice signals over the local loop, modems simply send an analog signal to the PSTN and expect to receive an analog signal from the PSTN. However, that analog signal represents some bits that the computer needs to send to another computer, instead of...

Analyzing and Interpreting IP Addresses and Subnets

No one reading this book should be shocked to hear that IP addressing is one of the most important topics on both exams. You need a comfortable, confident understanding of IP addressing and subnetting for success on any Cisco certification. You should be prepared to answer questions about the following An interpretation of an address The other IP addresses in the same subnet The other subnets that could be used if the same mask were in use In other words, you had better know IP addressing and...

ATM and SONET

Asynchronous Transfer Mode (ATM) and Synchronous Optical Network (SONET) together provide the capability for a telco to provide high-speed services for both voice and data over the same network. SONET defines a method for transmitting digital data at high speeds over optical cabling, and ATM defines how to frame the traffic, how to address the traffic so that DTE devices can communicate, and how to provide error detection. In short, SONET provides Layer 1 features, and ATM provides Layer 2...

Balanced Hybrid Protocols Enhanced IGRP

EIGRP does not use distance vector or link-state logic, but instead it uses a whole new category of routing protocol. This new category has some features similar to link-state protocols, others similar to distance vector protocols, and yet others unlike either of the two. Cisco sometimes categorizes EIGRP as a balanced hybrid protocol, so you should remember the term. The internal workings of EIGRP depend on an algorithm called the Diffusing Update Algorithm (DUAL). DUAL exchanges more topology...

BASET Ethernet

10BASE-T solved several problems with the early Ethernet specifications. 10BASE-T allowed the use of telephone cabling that was already installed, or simply allowed the use of cheaper, easier-to-install cabling when new cabling was required. 10BASE-T networks make use of devices called hubs, as shown in Figure 3-5. 10BASE-T, Using Shared Hub - Acts Like Single Bus 10BASE-T, Using Shared Hub - Acts Like Single Bus Solid Lines Represent Twisted Pair Cabling Solid Lines Represent Twisted Pair...

BASET Hubs

Compared to 10BASE2 and 10BASE5, hubs solved some cabling and availability problems. However, the use of hubs allowed network performance to degrade as utilization increased, just like when 10BASE2 and 10BASE5 were used, because 10BASE-T still created a single electrical bus shared among all devices on the LAN. Ethernets that share a bus cannot reach 100 percent utilization because of collisions and the CSMA CD arbitration algorithm. To solve the performance problems, the next step was to make...

Basic Administrative Configuration

Chapter 7 focused on the configuration process more than the actual configuration commands that happened to be in the chapter. Before you configure IP, this short section reviews some of the basic commands you typically will configure on any router. On most routers, you would configure at least the following Reference to a DNS so that commands typed on the router can refer to host names instead of IP addresses Set a password for those Telnetting to the router Set the enable secret password to...

Basic Router Configuration and Operation

To configure a Cisco router to route TCP IP packets, you typically configure an IP address and subnet mask on each interface. You also typically configure a dynamic routing protocol, which discovers the routes in a network. That's all the configuration that is required to make a Cisco router route IP packets. In this chapter, you will read about the basic commands to configure IP addresses and IP routing on a Cisco router. You also will read about a variety of commands that you can use to...

Book Features

To help you customize your study time using these books, the core chapters have several features that help you make the best use of your time Do I Know This Already Quizzes Each chapter begins with a quiz that helps you determine the amount of time you need to spend studying that chapter. If you follow the directions at the beginning of the chapter, the Do I Know This Already quiz directs you to study all or particular parts of the chapter. Foundation Topics These are the core sections of each...

Boot Protocol BOOTP

Dynamic Host Configuration Protocol (DHCP) RARP and BOOTP work using the same basic process. To use either protocol, a PC needs a LAN interface card. The computer sends a LAN broadcast frame announcing its own MAC address and requests that someone assign it an IP address. Figure 5-11 outlines the process for both RARP and BOOTP. Hey Everybody My MAC Address Is 0200.1111.1111. If You Are a RARP Server, Please Tell Me My IP Address 0200.1111.1111 10.1.1.1 0200.1234.567810.1.1.2 0200.5432.1111...

Cable Modem Summary

Like DSL, cable modems bring high-speed remote access capabilities to the home. The speeds might seem astounding 30 to 40 Mbps downstream is indeed impressive. In fact, I had a cable modem a few years ago and was one of the first people in my neighborhood to get it. I surfed the web much faster from home than I did from the local Cisco Systems office The data service is always on, even when someone is watching TV. Because it doesn't use the telephone line at all, you also can use the phone at...

Cable Modems

Of all the access technologies covered in this chapter, cable modems are the only one not using a phone line from the local telco for physical connectivity. Many homes also have a cable TV service supplied by an analog electrical signal entering the home over a coaxial cable in other words, over the cable TV cabling. Cable modems provide an always-on Internet access service, while allowing you to surf the Internet over the cable and make all the phone calls you want over your telephone line and...

Cabling and Connectors

Practically every other Cisco certification exam ignores the topic of cabling those exams just assume that you can read the manuals and figure out what cables are needed. Interestingly, a well-designed cabling plan, with the right cables, can be a big component of making a LAN more manageable and available. So, cabling is indeed important in real networks. The cables themselves contain different components inside the cable you just have to cut one open to look inside to see internal components....

Ccna Intro Exam Certification Guide

Copyright 2004 Cisco Systems, Inc. 201 West 103rd Street Indianapolis, IN 46290 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Library of Congress...

Cidr

CIDR is a convention defined in RFC 1817 (www.ietf.org rfc rfc1817.txt) that calls for aggregating multiple network numbers into a single routing entity. CIDR actually was created to help the scalability of Internet routers imagine a router in the Internet with a route to every Class A, B, and C network on the planet There are actually a little more than two million Class C networks alone By aggregating the routes, Internet routers have a significantly smaller number of routes in their routing...

Cisco ISL

Cisco created ISL before the IEEE standardized a trunking protocol. Because ISL is Cisco proprietary, it can be used only between two Cisco switches. ISL fully encapsulates each original Ethernet frame in an ISL header and trailer, with the encapsulated original Ethernet frame being unchanged. Figure 10-4 shows the framing for ISL. The ISL header includes several fields, but most important, the ISL header VLAN field provides a place to encode the VLAN number. By tagging a frame with the correct...

Cisco LAN Switching Basics

Cisco switches can perform the functions detailed in this chapter without any configuration. You can buy several switches, turn on the power, and cable the devices to the switch and everything works So, if the CCNA INTRO exam wanted to test you about only things you have to do to a switch to get it working, you would not even need this chapter. Of course, Cisco wants you to know how switches work. Not only is that necessary for the CCNA exams, but it also helps you in a job as a network...

Cisco Published Intro Exam Topics Covered in This Part

13 Define and describe the structure and technologies of computer networks 14 Describe the hardware and software required to be able to communicate via a network 15 Describe the physical, electrical and mechanical properties and standards associated with optical, wireless and copper media used in networks 16 Describe the topologies and physical issues associated with cabling common LANs 17 Identify the key characteristics of common wide area networking (WAN) configurations and technologies, and...

CLI Help Features

If you printed the IOS Command Reference documents, you would end up with a stack of paper several feet tall. No one should expect to memorize all the commands and no one does in real life, either. Several very easy, convenient tools can be used to help you remember commands and then also save you time typing. As you progress through your Cisco certifications, the exams will cover progressively more commands. However, you should know the methods of getting command help. Table 7-3 summarizes...

Coaxial Cabling

Coaxial cabling was used for 10BASE2 and 10BASE5 Ethernet in years past. 10BASE5 was referred to as thicknet, and 10BASE2 was referred to as thinnet because 10BASE5 used thicker coaxial cable. Even 10 years ago, newly installed Ethernet networks most often were not 10BASE2 or 10BASE5 networks, but rather were 10BASE-T. I personally have not seen a 10BASE2 or 10BASE5 Ethernet NIC available for sale from a vendor for at least 5 years. So, the relative importance of remembering the details of...

Command Syntax Conventions

The conventions used to present command syntax in this book are the same conventions used in the Cisco IOS Command Reference. The Command Reference describes these conventions as follows Vertical bars (I) separate alternative, mutually exclusive elements. Square brackets indicate optional elements. Braces indicate a required choice. Braces within brackets indicate a required choice within an optional element. Boldface indicates commands and keywords that are entered literally as shown. In...

Comparing and Contrasting IP Routing Protocols

Routing protocols can be categorized in several ways. One distinction is whether the protocol is more useful between two companies or inside a single company. Only one IP routing protocol that is popular today, the Border Gateway Protocol (BGP), is designed specifically for use between two different organizations. In fact, BGP distributes routing information between ISPs worldwide today and between ISPs and their customers as need be. Routing protocols that are best used to distribute routes...

Configuring 2950 IOS Software

The configuration process and the configuration files used are identical when comparing the router IOS behavior and a 2950 switch. So there is nothing more to learn compared with the router IOS. In other words, the following are true You use the configure terminal command from enable mode to enter configuration mode. Your configuration commands change the configuration of the switch the instant you press Enter at the end of each command. The help shown in configuration mode changes, depending...

Configuring Cisco IOS Software

You must understand how to configure a Cisco router to succeed on the exam or to succeed in supporting Cisco routers. This section covers the basic configuration processes, including the concept of a configuration file and the locations in which the configuration files can be stored. Configuration mode is another mode for the Cisco CLI, similar to user mode and privileged mode. User mode allows commands that are not disruptive to be issued, with some information being displayed to the user....

Configuring IP Addresses

You easily can configure a Cisco router to forward IP traffic when you understand IP addressing and the IOS configuration process described in Chapter 7, Operating Cisco Routers. This chapter shows you examples of a variety of commands used to configure and troubleshoot the routing of IP packets in a Cisco router. Tables 13-2 and 13-3 summarize many of the most common commands used for IP configuration and verification. You can refer to other sources for more information about basic IP...

Connection Establishment and Termination

TCP connection establishment occurs before any of the other TCP features can begin their work. Connection establishment refers to the process of initializing sequence and acknowledgment fields and agreeing to the port numbers used. Figure 6-8 shows an example of connection establishment flow. Figure 6-8 TCP Connection Establishment SYN, ACK, DPORT 1027, SPORT 80 < - SEQ 201, ACK 1451 ACK, DPORT 80, SPORT 1027 This three-way connection-establishment flow must complete before data transfer can...

Considerations When Using Net Sim

NetSim is a wonderful product, and you can certainly get a lot of good hands-on experience using the NetSim product that is included with the book. However, like any simulator product, it does not mimic a network with 100 accuracy. Some situations are difficult to simulate. For instance, it is very challenging to simulate the output of debug commands, because the simulator is not actually running IOS. If you intend to use NetSim, please download the latest list of hints, tips, and caveats from...

Contents

Introduction xvii Part I Networking Fundamentals 3 Chapter 1 Introduction to Computer Networking Concepts 5 The Flintstones Network The First Computer Network 7 Chapter 2 The TCP IP and OSI Networking Models 15 Do I Know This Already Quiz 16 Foundation Topics 20 The TCP IP Protocol Architecture 21 The TCP IP Application Layer 22 The TCP IP Transport Layer 24 The TCP IP Internetwork Layer 26 The TCP IP Network Interface Layer 27 Data Encapsulation 29 OSI Reference Model 31 OSI Layers 31 OSI...

Converting Analog Voice to Digital Voice

The last step in understanding how the PSTN supports voice across a digital PSTN relates to how the PSTN converts the analog electrical signals to digital signals, and vice versa. To see the need for the conversion, examine Figure 15-4. Figure 15-4 Analog Voice Calls Through a Digital PSTN Figure 15-4 Analog Voice Calls Through a Digital PSTN When Andy calls Barney in Raleigh, the circuit is set up by the telco. (Yes, Barney moved to Raleigh since the last example.) And it works It works...

Creating VLANs

Switches normally define VLANs in terms of which ports are in each VLAN. You literally configure something as simply as interface 0 1 is in VLAN 1 and interface 0 2 is in VLAN 33. Port-based VLANs, the typical choice for configuring VLANs in a switch, can be done very easily, without needing to know the MAC address of the device. However, you need good documentation to make sure that you cable the right devices into the right switch port, thereby putting them in the right VLANs. A rarely used...

Data Link Function 1 Arbitration

Imagine trying to get through an intersection in your car when all the traffic signals are out you all want to use the intersection, but you had better use it one at a time. You finally get through the intersection based on a lot of variables on how tentative you are, how big the other cars are, how new or old your car is, and how much you value your own life Regardless, you cannot allow cars from every direction to enter the intersection at the same time without having some potentially serious...

Data Link Function 2 Addressing

When I sit and have lunch with my friend Gary, and just Gary, he knows I am talking to him. I don't need to start every sentence by saying Hey, Gary Now imagine that a few other people join us for lunch I might need to say something like Hey, Gary. before saying something so that Gary knows I'm talking to him. Data-link protocols define addresses for the same reasons. Many physical networks allow more than two devices attached to the same physical network. So, data-link protocols define...

Data Link Function 3 Error Detection

Error detection discovers whether bit errors occurred during the transmission of the frame. To do this, most data-link protocols include a frame check sequence (FCS) or cyclical redundancy check (CRC) field in the data-link trailer. This field contains a value that is the result of a mathematical formula applied to the data in the frame. An error is detected when the receiver plugs the contents of the received frame into a mathematical formula. Both the sender and the receiver of the frame use...

Data Link Function 4 Identifying the Encapsulated Data

Finally, the fourth part of a data link identifies the contents of the Data field in the frame. Figure 3-3 helps make the usefulness of this feature apparent. The figure shows a PC that uses both TCP IP to talk to a web server and Novell IPX to talk to a Novell NetWare server. Figure 3-3 Multiplexing Using Data-Link Type and Protocol Fields When PC1 receives data, should it give the data to the TCP IP software or the NetWare client software Of course, that depends on what is inside the Data...

Data Link Layer Fundamentals Ethernet LANs

As you learned in the previous chapter, OSI Layers 1 and 2 map closely to the network interface layer of TCP IP. In this chapter, you will learn more details about the functions of each of the two lowest layers in the OSI reference model, with specific coverage of Ethernet local-area networks (LANs). The introduction to this book mentioned that the INTRO exam covers some topics lightly and covers others to great depth. As implied in the title, this chapter hits the fundamentals of Ethernet,...

Digital Subscriber Line

Any two computers using compatible modems could communicate with each other. Those computers might just be two PCs, a PC dialing into a router or access server at one of the business offices, or a PC dialing into a router or access server at an ISP. As long as both endpoints have a compatible modem, the two can communicate. By the time DSL came around in the mid- to late 1990s, the main goal for remote access was not the capability to connect to any site anywhere, but to connect to either the...

Distance Vector Protocols RIP and IGRP

Distance vector protocols advertise routing information by sending messages, called routing updates, out the interfaces on a router. These updates contain a series of entries, with each entry representing a subnet and a metric. The metric represents how good the route is from that router's perspective, with a smaller number being a better route. Any routers that receive a copy of a distance vector routing update receive that information and possibly add some routes to their routing table. The...

Do I Know This Already Quiz

The purpose of the Do I Know This Already quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. The ten-question quiz, derived from the major sections in Foundation Topics portion of the chapter, helps you determine how to spend your limited study time. Table 3-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions...

DSL Protocols

DSL itself provides a Layer 1 transmission path between two endpoints, in some ways like the Layer 1 service that analog modems and ISDN modems provide. However, DSL uses some additional protocols to support data transfer. For instance, DSL uses ATM as the Layer 2 protocol between the DSL router or DSL modem in the home and the ISP router. Additionally, DSL uses a protocol called PPP over ATM (PPPoA). PPP and ATM are both data-link protocols, but they serve different purposes. PPP provides...

DSL Standards

DSL comes in many flavors to meet different needs. For instance, DSL has limits on how long the local loop can be (the length of the local loop is simply the length of the combined cables that stretch from a house to the CO). Some DSL variants allow the local loop to be much longer, while others allow for only a shorter local loop. For the standards with a shorter local loop, the transmission rates tend to be much higher a simple design trade-off. ADSL and SDSL tend to be the most popular...

DSL Summary

DSL provides OSI Layer 1 and Layer 2 services to the home. The goal of DSL is to deliver IP packets from the remote user to a router a router owned by an ISP, or a router resident inside a corporate network. To do so, DSL provides a digital Layer 1 service serial bit streams in each direction between the remote site and the local CO. On top of that, DSL uses a combination of ATM, Ethernet, and PPP to help deliver IP packets between the home and a router at an ISP. DSL brings high-speed remote...

Early Ethernet Standards

Now that you have a little better understanding of some of the functions of physical and data link standards, the next section focuses on Ethernet in particular. This chapter covers some of the basics, while Chapters 9 through 11 cover the topics in more detail. In this section of the chapter, you learn about the three earliest types of Ethernet networks. The term Ethernet refers to a family of protocols and standards that together define the physical and data link layers of the world's most...

Eliminating Collisions to Allow Full Duplex Ethernet

The original Ethernet specifications used a shared bus, over which only one frame could be sent at any point in time. So, a single device could not be sending a frame and receiving a frame at the same time because it would mean that a collision was occurring. So, devices simply chose not to send a frame while receiving a frame. That logic is called half-duplex logic. Ethernet switches allow multiple frames to be sent over different ports at the same time. Additionally, if only one device is...

Error Recovery Reliability

TCP provides for reliable data transfer, which is also called reliability or error recovery, depending on what document you read. To accomplish reliability, TCP numbers data bytes using the Sequence and Acknowledgment fields in the TCP header. TCP achieves reliability in both directions, using the Sequence Number field of one direction combined with the Acknowledgment field in the opposite direction. Figure 6-5 shows the basic operation. In Figure 6-5, the Acknowledgment field in the TCP header...

Ethernet 10BASET Cabling

The PCs and hub in Figure 3-5 typically use Category 5 UTP cables with RJ-45 connectors, as shown in Figure 3-2. The Ethernet cards in each PC have an RJ-45 connector, as does the hub these connectors are larger versions of the same type of connector used for telephone cords between a phone and the wall plate in the United States. So, connecting the Ethernet cables is as easy as plugging in a new phone at your house. The details behind the specific cable used to connect to the hub are important...

Ethernet Addressing

Ethernet LAN addressing identifies either individual devices or groups of devices on a LAN. Unicast Ethernet addresses identify a single LAN card. Each address is 6 bytes long, is usually written in hexadecimal, and, in Cisco devices, typically is written with periods separating each set of four hex digits. For example, 0000.0C12.3456 is a valid Ethernet address. The term unicast addresses, or individual addresses, is used because it identifies an individual LAN interface card. (The term...

Ethernet Cabling Standards

Each IEEE Ethernet standard defines the details for supporting a particular speed over a particular type of cabling. Also, each of these definitions specifies the maximum cable length and the required features of the cabling. Tables 11-5, 11-6, and 11-7 list the pertinent details of the standards, and the cabling. Table 11-5 Ethernet 802.3 Cabling Standards Table 11-5 Ethernet 802.3 Cabling Standards Table 11-6 Fast Ethernet 802.3u Cabling Standards Table 11-6 Fast Ethernet 802.3u Cabling...

Ethernet Data Link Protocols

One of the most significant strengths of the Ethernet family of protocols is that these protocols use the same small set of data-link protocols. For instance, Ethernet addressing works the same on all the variations of Ethernet, even back to 10BASE5. This section covers most of the details of the Ethernet data-link protocols.

Ethernet Framing

Framing defines how a string of binary numbers is interpreted. In other words, framing defines the meaning behind the bits that are transmitted across a network. The physical layer helps you get a string of bits from one device to another. When the receiving device gets the bits, how should they be interpreted The term framing refers to the definition of the fields assumed to be in the data that is received. In other words, framing defines the meaning of the bits transmitted and received over a...

Ethernet Standards

Back in Chapter 3, this book introduced you to the most important Ethernet standards. Those included the IEEE 802.3 standard, including the Media Access Control (MAC) sublayer, which defines the 6-byte Ethernet addresses. Ethernet also uses IEEE 802.2, which defines a sublayer called Logical Link Control (LLC). 802.2 includes the DSAP field, which identifies the type of packet held in an Ethernet frame. Also in that chapter, you learned the main IEEE standards for Fast Ethernet (802.3u) and...

Fast Ethernet

Fast Ethernet, as defined in IEEE 802.3u, retains many familiar features of 10-Mbps IEEE 802.3 Ethernet variants. The age-old CSMA CD logic still exists, but it can be disabled for full-duplex point-to-point topologies in which no collisions can occur. The 802.3u specification calls for the use of the same old IEEE 802.3 MAC and 802.2 LLC framing for the LAN headers and trailers. A variety of cabling options is allowed unshielded and shielded copper cabling as well as multimode and single-mode...

Feedback Information

At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community. Readers' feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book or otherwise alter it to better suit your needs, you can contact us through e-mail at...

Fiber Optic Cabling and Connectors for Ethernet

Fiber cabling, also called optical cabling or fiber optics, provides another option for cabling Ethernet. The main differences, in terms of function, between optical cabling for Ethernet and electrical cabling are as follows Longer distances supported by optical cabling Less magnetic interference, making it slightly more secure Only type of cabling supported by 10 Gig Ethernet For instance, network engineers might choose to use optical interfaces and cabling for Ethernet when building a campus...

Final Preparation

So, you have made it through most of the book, and you have probably either scheduled your INTRO exam or CCNA exam, or at least thought about when you want to try to take it. Congratulations for getting this far You will soon have finished your first step toward building your networking career r sum . This chapter provides some tips on your final preparation for the exam. It also provides an example scenario, which helps you to pull many of the hands-on skills together into a single review...

Flow Control Using Windowing

TCP implements flow control by taking advantage of the Sequence and Acknowledgment fields in the TCP header, along with another field called the Window field. This Window field implies the maximum number of unacknowledged bytes allowed outstanding at any instant in time. The window starts small and then grows until errors occur. The window then slides up and down based on network performance, so it is sometimes called a sliding window. When the window is full, the sender will not send, which...

Forwarding Unknown Unicasts and Broadcasts

What do you suppose the bridge did with Fred's first frame in Figure 9-4, the one that occurred when there were no entries in the bridging table As it turns out, when there is no matching entry in the table, bridges forward the frame out all interfaces. Bridges were designed to forward what are called unknown unicast frames (frames whose destination MAC addresses are not yet in the bridging table), with the hope that the unknown device will be on some other Ethernet segment and will reply, and...

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 INTRO 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. Table 2-6 summarizes the key points about how adjacent layers work together on a single computer and how one layer on one computer works with the same networking...

Foundation Topics

Ethernet is the undisputed king of LAN standards today. Fifteen years ago, people wondered whether Ethernet or Token Ring would become win the battle of the LANs. Eight years ago, it looked like Ethernet would win that battle, but it might lose to an upstart called Asynchronous Transfer Mode (ATM) in the LAN. Today when you think of LANs, no one even questions what type it's Ethernet. Ethernet has remained a viable LAN option for many years because it has adapted to the changing needs of the...

Frame Relay

Point-to-point WANs can be used to connect a pair of routers at multiple remote sites. However, an alternative WAN service, Frame Relay, has many advantages over point-to-point links, particularly when you connect many sites via a WAN. To introduce you to Frame Relay, I focus on a few of the key benefits compared to leased lines. One of the benefits is seen easily by considering Figures 4-7. Figure 4-7 Two Leased Lines to Two Branch Offices In Figure 4-7, a main site is connected to two branch...

Full Duplex Ethernet

Full-duplex Ethernet was explained back in Chapter 3. Briefly, when a switch port has only a single device attached to it, no collisions could possibly occur because there is only one connected device. So, the device cabled to that switch port disables its NIC loopback logic, allowing the device to both send a frame and receive a frame at the same time. If a hub with multiple devices is connected to a switch port, collisions still can occur, so half-duplex operation must be used. Figure 9-6...

Fundamentals of IP

The OSI model assigns the functions of path selection and logical addressing to the OSI network layer (Layer 3). Path selection includes the process of learning all the paths, or routes, in a network and then forwarding packets based on those paths or routes. Often the terms path selection and routing are used interchangeably. In most Cisco documentation and in this book, routing is the more popular term. In this chapter, you will learn about the core concepts behind OSI Layer 3. Because CCNA...

Fundamentals of TCP and UDP

The Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are the two most popular TCP IP transport layer protocols. These TCP IP protocols define a variety of functions considered to be OSI transport layer, or Layer 4, features. Some of the functions relate to things you see every day for instance, when you open multiple web browsers on your PC, how does your PC know which browser to put the next web page in When a web server sends you 500 IP packets containing the various parts...

General Features of Metallic Cabling

The term cable refers to a combination of plastics, metal wires, optical fibers, possibly rubber, and other materials molded into a cord of varying lengths. Well, that's at least a formal definition. People see cables every day. The power cords that go from the electrical wall socket to each of your electrically powered appliances and lamps at home are all cables. There are cables protruding from the back of your PC. And for networking, the phone cord stretching from the wall outlet to your...

Gigabit Ethernet

The IEEE defines Gigabit Ethernet in standards 802.3z for optical cabling and 802.3ab for electrical cabling. Like Fast Ethernet, Gigabit Ethernet retains many familiar features of slower Ethernet variants. CSMA CD still is used and can be disabled for full-duplex support. The 802.3z and 802.3ab standards call for the use of the same old IEEE 802.3 MAC and 802.2 LLC framing for the LAN headers and trailers. The most likely place to use Gigabit is between switches, between switches and a router,...

Hdlc

HDLC performs OSI Layer 2 functions, so a brief review of the OSI Layer 2 functions covered in Chapter 3, Data Link Fundamentals Ethernet LANs, will be helpful Arbitration Determines when it is appropriate to use the physical medium Addressing Ensures that the correct recipient(s) receives and processes the data that is sent Error detection Determines whether the data made the trip across the physical medium successfully Identifying the encapsulated data Determines the type of header that...

How Bridges Learn MAC Addresses

Bridges perform three main functions, as mentioned earlier. One of those key functions is to learn the MAC addresses in the network to build its bridging table. With a full, accurate bridging table, the bridge can make accurate forwarding and filtering decisions. Bridges build the bridge table by listening to incoming frames and examining the source MAC address in the frame. If a frame enters the bridge and the source MAC address is not in the bridge table, the bridge creates an entry in the...

How IP Addresses Are Grouped Together

To fully appreciate IP addressing, you first must understand the concepts behind the grouping of IP addresses. The first visions of what we call the Internet were for connecting research sites. A typical network diagram might have looked like Figure 5-3. Figure 5-3 Sample Network Using Class A, B, and C Network Numbers Figure 5-3 Sample Network Using Class A, B, and C Network Numbers The conventions of IP addressing and IP address grouping make routing easy. For example, all IP addresses that...

How Spanning Tree Works

The Spanning Tree Algorithm places each bridge or switch port into either a forwarding state or a blocking state. All the ports in the forwarding state are considered to be in the current spanning tree. The collective set of forwarding ports creates a single path over which frames are sent between Ethernet segments. Switches can forward frames out ports and receive frames in ports that are in a forwarding state switches do not forward frames out ports and receive frames in ports that are in a...

How to Use This Book to Prepare for the Intro Exam

To study for the INTRO exam, you can simply use this book and start reading. The study plan is simple. However, if you have some experience or knowledge of Cisco products and networking protocols already, you might be able to save a little study time while taking only small risks. Figure I-1 shows the progression you should take through the books as you prepare for the INTRO exam. In each chapter, an assessment quiz, called the Do I Know This Already Quiz, helps you decide whether you already...

How You Should Proceed with Net Sim

You can bring up NetSim and dive right in. However, here a a few suggestions before you are Bring up NetSim now, and make sure you can at least get to a router command prompt, using the PC you will most likely use when studying. That way, when you are ready to do your first lab or scenario, you know you have worked out any installation issues. If you intend to do most of the labs and scenarios, you might want to print CD-only Appendixes B and C. Decide if you prefer to do the labs and scenarios...

ICMP Echo and the ping Command

IP needs to have a way to test basic IP connectivity, without relying on any applications to be working. Hannah, being a great network troubleshooter (in spite of being my 2-year-old daughter), can test basic network connectivity using the ping command. ping (Packet INternet Groper) uses the Internet Control Message Protocol (ICMP), sending a message called an ICMP echo request to another IP address. The computer with that IP address should reply with an ICMP echo reply. If that works, you...

IEEE 80211 Wireless LANs

The most popular type of wireless LAN today is based on the IEEE 802.11 standard, which is known informally as Wi-Fi. The 802.11 specification defines what happens on the wireless network to let two or more devices send and receive data. Wireless LAN communication is really a shared LAN because only one station effectively can transmit at one time, at least in a particular constrained geography. 802.11 signals effectively might reach another device as far as 300 feet away. So, you can have lots...

IEEE 8021q

The IEEE standardizes many of the protocols relating to LANs today, and VLAN trunking is no exception. Years after Cisco created ISL, the IEEE completed work on the 802.1q standard, which defines a different way to do trunking. 802.1q uses a different style of header than does ISL for tagging frames with a VLAN number. In fact, 802.1q does not actually encapsulate the original frame instead, it adds an extra 4-byte header to the middle of the original Ethernet header. That additional header...

Integrated Services Digital Network

Integrated Services Digital Network (ISDN) provides switched (dialed) digital WAN services in increments of 64 kbps. Before ISDN, the only widely-available method to dial a circuit for data communication between two computers was to use analog modems. When ISDN was created, analog modem speeds typically did not even exceed 9600 bps. The phone companies of the world wanted to have a dialed service that not only allowed faster transmission rates, but also was pervasive as a simple analog line...

Internal Processing on Cisco Switches

Switches use a couple of different types of internal processing variations. Almost of the more recently released switches use store-and-forward processing, but all three types of switching are supported in at least one type of currently available Cisco switch. Some switches, and transparent bridges in general, use store-and-forward processing. With store-and-forward, the entire frame is received by the switch before the first bit of the frame is forwarded. However, Cisco also offers two other...

INTRO and ICND Course Outlines

Another way to get some direction about the topics on the exams is to look at the course outlines for the related courses. Cisco offers the Introduction to Cisco Networking (INTRO) and Interconnection Cisco Network Devices (ICND) courses through its Certified Learning Solutions Providers (CLSP) CLSPs, in turn, work with other learning partners as well. The INTRO course covers a much broader set of topics than does ICND, but for the topics it covers, ICND covers the topics to much greater...

Introduction to Dynamic Routing Protocols

The United States Postal Service routes a huge number of letters and packages each day. To do so, the postal sorting machines run fast, sorting lots of letters. Then the letters are placed in the correct container and onto the correct truck or plane to reach the final destination. However, if no one programs the letter-sorting machines to know where letters to each ZIP code should be sent, the sorter can't do its job. Similarly, Cisco routers can route many packets, but if the router doesn't...

IP Addressing and Subnetting

In Chapter 5, Fundamentals of IP, you learned about the basic concepts and terminology relating to IP addressing. These concepts were introduced early in the book because your understanding of many basic networking concepts depends on a base knowledge of IP addressing. In this chapter, you will learn about the concepts and mathematics that let you analyze IP addresses and subnets. IP addressing is the only major topic that happens to get coverage on both of the INTRO and ICND exams. To answer...

IP Addressing Definitions

If a device wants to communicate using TCP IP, it needs an IP address. When the device has an IP address and the appropriate software and hardware, it can send and receive IP packets. Any device that can send and receive IP packets is called an IP host. IP addresses consist of a 32-bit number, usually written in dotted-decimal notation. The decimal part of the term comes from the fact that each byte (8 bits) of the 32-bit IP address is converted to its decimal equivalent. The four resulting...

IP Addressing Fundamentals

No one reading this book should be shocked to hear that IP addressing is one of the most important topics for passing the the INTRO and ICND exams. In fact, IP addressing is the only major topic that is covered specifically on both the INTRO and ICND exams. Plus, you need a comfortable, confident understanding of IP addressing and subnetting for success on any Cisco certification. In other words, you had better know addressing and subnetting This section introduces IP addressing and subnetting,...

IP Addressing Review

Chapter 5 explained the concepts behind IP addressing Class A, B, and C networks and subnetting. Before looking at the math behind IP addressing, a quick review will be helpful. Many different Class A, B, and C networks exist. Table 12-2 summarizes the possible network numbers, the total number of each type, and the number of hosts in each Class A, B, and C network. Table 12-2 List of All Possible Valid Network Numbers* Table 12-2 List of All Possible Valid Network Numbers* Size of Network Part...

IP Naming Commands

When using the IOS CLI, you will want to refer to names instead of IP addresses. Particularly for the trace, ping, and telnet commands, the IP address or host name must be supplied. This section describes the use of host names on an IOS-based device. Along the way, some nuances of the use of Telnet are covered. IOS can use statically configured names as well as refer to one or more DNSs. Example 13-9 shows some names statically configured, with configuration pointing to two different DNSs....

IP Routing and Routing Protocols

In the first section of this chapter, you read about the basics of routing using a network with three routers and two PCs. Armed with more knowledge of IP addressing, you now can take a closer look at the process of routing IP. Figure 5-13 repeats the familiar network diagram, this time with subnets of network 150.150.0.0 used. Figure 5-13 Simple Routing Example, with IP Subnets Subnet Out Interface Next Hop IP Address 150.150.4.0 Serial0 150.150.2.7 Subnet Out Interface Next Hop IP Address...

IP Routing Protocols

IP routing protocols fill the IP routing table with valid, (hopefully) loop-free routes. Each route includes a subnet number, the interface out which to forward packets so that they are delivered to that subnet, and the IP address of the next router that should receive packets destined for that subnet (if needed). Before examining the underlying logic, you need to consider the goals of a routing protocol. The goals described in the following list are common for any IP routing protocol,...

IP Subnetting

IP subnetting creates vastly larger numbers of smaller groups of IP addresses, compared with simply using Class A, B, and C conventions. The Class A, B, and C rules still exist but now a single Class A, B, or C network can be subdivided into many smaller groups. Subnetting treats a subdivision of a single Class A, B, or C network as if it were a network itself. By doing so, a single Class A, B, or C network can be subdivided into many nonoverlapping subnets. Figures 12-2 and 12-3 show the basic...

IP Version 6 Addressing

The short-term solution to the problem of depleting the entire IPv4 address space included NAT and private addressing. CIDR provider a short-term solution to the growing size of IP routing tables. The long-term solution to both problems, at least according to some, is to use a new version of the IP protocol Version 6 (IPv6). (The version discussed in this book is Version 4. Version 5 was defined for experimental reasons and never was deployed.) IPv6 calls for a much larger address structure so...

ISDN Call Setup and Data Link Protocols

Call setup differs between ISDN and modems. With a telephone call and with analog modems, DTMF tones are sent across the analog local loop to the telco. The telco switch at the local CO interprets the dialed digits and sets up the call. However, with ISDN, there is no analog local loop over which the analog DTMF tones can be sent. ISDN devices send and receive signaling messages to and from the local ISDN switch to which it is connected. In telco terminology, signaling refers to any type of...

ISDN Channels

ISDN includes two types of lines Basic Rate Interface (BRI) and Primary Rate Interface (PRI). Both BRI and PRI provide multiple digital bearer channels (B channels) over which data can be sent and received. Because both BRI and PRI have multiple B channels, a single BRI or PRI line can have concurrent digital dial circuits to multiple sites. Alternately, you can create multiple circuits to the same remote site to increase available bandwidth to that site. B channels transport data. They operate...

ISDN Installation and Cabling

ISDN installation for a home-based PC works much like it does for modems. The most popular option uses an external ISDN modem, or terminal adapter. Figure 15-12 depicts the typical cabling. Figure 15-12 Cabling a PC to an ISDN TA In this case, a COM port (shown) or a USB port (not shown) connects to the TA. The TA terminates the ISDN cable from the telco. The cable from the telco uses an RJ-45 connector, the same type used for Ethernet cables. However, the pins used inside the cable are...

ISDN Summary

ISDN supports a BRI service with 2 B channels, and a PRI service with either 23 (T1) or 30 (E1) B channels. Signaling for call setup and teardown occurs over an out-of-band D channel. After a circuit has been established over a B channel, ISDN provides a Layer 1 service, delivering a serial bit stream between the two endpoints of the circuit. ISDN's advantages include the capability to support voice calls concurrently with a data call. Also, ISDN can be used over the local telco loop, with no...

ISL and 8021q Compared

Both ISL and 802.1q provide trunking. The header used by each varies, and only ISL actually encapsulates the original frame, but both allow the use of a 12-bit-long VLAN ID field. So, either works fine and supports the same number of VLANs as a result of both using a 12-bit VLAN Number field. ISL and 802.1q both support a separate instance of spanning tree for each VLAN. ISL supported this feature much earlier than did 802.1q, so in years past, one of the stated differences between the two...

LAN Cabling Standards and Topologies

This chapter completes the Ethernet puzzle for this book, in relation to the requirements of the INTRO exam. Ethernet was covered in several other chapters of this book specifically, Chapter 3, Data Link Layer Fundamentals Ethernet LANs, Chapter 9, Cisco LAN Switching Basics, and Chapter 10, Virtual LANs and Trunking. The topics in those chapters laid the foundation of a relatively broad knowledge of Ethernet. However, to keep those chapters flowing and not get bogged down in some long tangents...

LAN Switching

Before bridges were created, a 10BASE-T network might have begun to suffer from performance problems. As described in the previous section, to improve performance, you might have added a two-port bridge, created two LAN segments, doubled the bandwidth, reduced collisions, and improved performance. Now take a step back and think about what might happen to that network with the bridge 6 months later. More devices have been added to the segments on each side of the bridge. More bandwidth-hungry...

Layer 2 Ethernet Summary

As mentioned earlier in this chapter, physical layer protocols define how to deliver data across a physical medium. Data-link protocols make that physical network useful by defining how and when the physical network is used. Ethernet defines the OSI Layer 1 functions for Ethernet, including cabling, connectors, voltage levels, and cabling distance limitations, as well as many important OSI Layer 2 functions. In this section, four of these data link features were emphasized, as shown in Table...