A

Note that each IP datagram carries this header, which includes a source IP address and destination IP address that identify the source and destination network and host. An IP address is a hierarchical address, and it consists of two parts The high order, or leftmost, bits specify the network address component (network ID) of the address. The low order, or rightmost, bits specify the host address component (host ID) of the address. Every physical or virtual LAN on the corporate internetwork is...

Gso

Catalyst switches, 178 Cisco routers, 307 acknowledgments, 79-80 active attacks, 27 ad hoc mode (802.11), 222 address classes, 46-49 address exhaustion, 54-57 address resolution, 88 addressing, Ethernet, 113 addressing scheme, determining, 264-265 Class A networks, 268, 270 Class B networks, 267-268 Class C networks, 265, 267 administrative distance, 397-398 ADSL (asynchronous DSL), 359 application layer OSI model, 34 TCP IP model, 41 applications, TCP IP, 67 APs (access points) BSA, 223...

Aa

L2 0800 0222 2222 L2 0800 0333 2222 L2 0800 0333 1111 L2 0800 0222 1111 To be able to move data from one network to another, there must be some type of Layer 3 addressing that can uniquely identify both the network and the host. For this example, we will be using IP as the Layer 3 addressing. Figure 4-30 shows the Layer 3 addressing for each device along the path. The router has its own Layer 3 address on each interface. This will be the gateway address for the client on each subnet and, along...

About the Author

Steve McQuerry, CCIE No. 6108, is a consulting systems engineer with Cisco Systems focused on data center architecture. Steve works with enterprise customers in the midwestern United States to help them plan their data center architectures. Steve has been an active member of the internetworking community since 1991 and has held multiple certifications from Novell, Microsoft, and Cisco. Prior to joining Cisco, Steve worked as an independent contractor with Global Knowledge, where he taught and...

Accessing Remote Devices

During routine maintenance, it is often desirable to access a device from another device. Cisco IOS Software provides a set of tools for this purpose. The following sections describe methods that you can use to access remote devices. Establishing a Telnet or SSH Connection Telnet or Secure Shell (SSH) applications are useful for connecting to remote devices. One way to obtain information about a remote network device is to connect to it using either the Telnet or SSH applications. Telnet and...

Ack

TCP, UDP, and IP and their headers are key in the communications between networks. Layer 3 devices use an internetwork protocol like TCP IP to provide communications between remote systems. TCP performs sequencing of segments with a forward reference acknowledgment. A forward reference acknowledgment comes from the receiving device and tells the sending device which segment the receiving device is expecting to receive next. For the purpose of this lesson, the complex operation of TCP is...

Ack 5

Each acknowledgment transmitted by the receiver contains a window advertisement that indicates the number of bytes the receiver can accept (the window size). This allows the window to be expanded or contracted as necessary to manage buffer space and processing. TCP maintains a separate congestion window size (CWS) parameter, which is normally the same size as the window size of the receiver, but the CWS is cut in half when segments are lost. Segment loss is perceived as network congestion. TCP...

Acknowledgments

There are a great number of people that go into publishing a work like this, and I would like to take this space to thank everyone who was involved with this project. Thanks to the ICND course developers. Most of this book is the product of their hard work. Thanks to the technical editors, Tami Day-Orsatti, Kevin Wallace, and Matt Brussel, for looking over this work and helping maintain its technical integrity. Thanks to all the real publishing professionals at Cisco Press. This is a group of...

Adversaries Hacker Motivations and Classes of Attack

To defend against attacks on information and information systems, organizations must define the threat in these three terms Adversaries Potential adversaries might include nation-states, terrorists, criminals, hackers, disgruntled employees, and corporate competitors. Hacker motivations Hackers' motivations might include intelligence gathering, the theft of intellectual property, denial of service (DoS), the embarrassment of the company or clients, or the challenge of exploiting a notable...

Am

Table 4-12 show ip dhcp conflict Command Field Descriptions Table 4-12 show ip dhcp conflict Command Field Descriptions The IP address of the host as recorded on the DHCP server The manner in which the IP addresses of the hosts were found on the DHCP server, which can be a ping or a gratuitous ARP The date and time when the conflict was found Summary Using a Cisco Router as a DHCP Server The following list summarizes the key points that were discussed in the previous sections DHCP is built on a...

App Data

IP Layer 2 send this to 192.168.4.2. L3 192.168.3.1 L2 0800 0222 2222 L3 192.168.3.2 L2 0800 0333 2222 L3 192.168.4.1 L2 0800 0333 1111 L3 192.168.4.2 L2 0800 0222 1111 Figure 4-33 Determine Host Is on a Different Subnet Parking Lot IP I am on 192.168.3.0 24 and the destination is on 192.168.4.0 24, so we are on different segments. I'll have to use the default gateway. ARP My default gateway is 192.168.3.2, but I don't have its MAC address. I'll have to ARP....

Arp

Layer 3 192.168.3.1 Layer 2 0800 0222 2222 Layer 3 192.168.3.2 Layer 2 0800 0222 1111 Layer 2 encapsulates the ARP in a Layer 2 frame using the destination MAC address provided by ARP and the local source MAC address. Figure 1-72 shows this operation. Figure 1-72 ARP Responds Parking Lot Layer 3 192.168.3.1 Layer 2 0800 0222 2222

Arpa

Table 4-8 show ip arp Command Output Fields Table 4-8 show ip arp Command Output Fields Protocol for network address in the Address field. The network address that corresponds to the Hardware Address. Age in minutes of the cache entry. A hyphen (-) means that the address is local. LAN hardware address of a MAC address that corresponds to the network address. Indicates the encapsulation type that the Cisco IOS Software is using in the network address in this entry. Possible values include the...

Atm

When a Cisco device boots, CDP starts by default, and automatically discovers neighboring Cisco devices running CDP, regardless of which protocol suite is running. Figure 6-2 displays an example of how CDP exchanges information with its directly connected neighbors. You can display the results of this information exchange on a console connected to a network device configured to run CDP on its interfaces. Figure 6-2 CDP Works Between Neighbor Devices Figure 6-2 CDP Works Between Neighbor Devices...

B

B Occurs when RF waves bounce off metal or glass surfaces A Occurs when RF waves are soaked up by walls C Occurs when RF waves strike an uneven surface and are reflected in many directions 16. A Mobile clients connect directly without an intermediate access point. B The communication devices use a single access point for connectivity to each other or to wired network resources. C The wireless topology is two or more service sets connected by a distribution system (DS) or, more commonly, a wired...

Balancing Network Security Requirements

The overall security challenge is to find a balance between two important needs open networks to support evolving business requirements and freedom-of-information initiatives versus the protection of private, personal, and strategic business information. Figure 1-19 shows the relationship between expanding the business value and increasing security risks. Security has moved to the forefront of network management and implementation. The survival of many businesses depends on allowing open access...

Basecx

Gigabit Ethernet over copper cabling You can add devices to an Ethernet LAN to extend segments. This topic describes how adding repeaters or hubs can overcome the distance limitation in an Ethernet LAN. A repeater is a physical layer device that takes a signal from a device on the network and acts as an amplifier. Adding repeaters to a network extends the segments of the network so that data can be communicated successfully over longer distances. There are, however, limits on the number of...

Bbe3

K N> ipconfig all Windows IP Configuration IP Routing Enabled. . . WINS Proxy Enabled. . . DNS Suffix Search List. Ethernet adapter Local Area Connection Connection specific DNS Suffix Description Physical Address Dhcp Enabled. . Autoconf iguratioi IP Address. . . Subnet Mask . . Default Gateway DHCP Server . . DNS Seruers . . Lease Obtained. UMware Accelerated AMD PCNet Adapterl

Building a Simple Network

When you are building a network, the tasks and components can sometimes be overwhelming. The key to understanding how to build a computer network lies in understanding the foundations of network communications. The key to building a complex network involves gaining an understanding of the physical and logical components of a simple point-to-point network. To become proficient in networking, you must gain knowledge of why networks are built and the protocols used in modern network designs. This...

Bus Topology

The bus topology is commonly referred to as a linear bus all of the devices on a bus topology are effectively connected by one single cable. As illustrated in Figure 1-8, in a bus topology, a cable proceeds from one computer to the next like a bus line going through a city. The main cable segment must end with a terminator that absorbs the signal when it reaches the end of the line or wire. If no terminator exists, the electrical signal representing the data bounces back at the end of the wire,...

C

If you are addressing a nonpublic intranet, these private addresses can be used instead of globally unique addresses. If you want to connect a network using private addresses to the Internet, however, it is necessary to translate the private addresses to public addresses. This translation process is referred to as Network Address Translation (NAT). A router is often the network device that performs NAT. The growth of the Internet has resulted in enormous demands for IP addresses. This section...

C H A P T E R

When sites are located at different geographic locations, a WAN provides interconnections between the sites. WANs are most often charge-for-service networks, enabling you to access resources across a wide geographical area. Several types of WANs exist, including point-to-point leased lines, circuit-switched networks, and packet-switched networks. Also, many physical network devices are used in the WAN, as well as many access and encapsulation technologies such as digital subscriber line (DSL),...

Chapter

C 3. security A 4. availability E 5. scalability B 6. reliability F 7. topology 10. B 1. All of the network devices connect directly to each other in a linear fashion. A 2. All of the network devices are directly connected to one central point with no other connections between them. D 3. All of the devices on a network are connected in the form of a circle. C 4. Each device has a connection to all of the other devices. E 5. At least one device maintains multiple connections to other devices. F...

Chapter Objectives

Upon completing this chapter, you will be able to create a simple point-to-point network and describe network components and functions. These abilities include meeting these objectives Identify the benefits of computer networks and how they function Identify common threats to a network and threat-mitigation methods Identify and compare the Open System Interconnection (OSI) and TCP IP layered models that control host-to-host communications Describe IP address classification and how a host can...

Chapter Organization

This book is divided into six chapters and is designed to be read in order because many chapters build on content from previous chapters. Chapter 1, Building a Simple Network, describes the principles on which basic networks operate. This chapter helps build a foundational understanding that is used throughout the other chapters of the book. Chapter 2, Ethernet LANs, explores the operation and configuration of LANs, including the challenges associated with these networks, and describes how...

Chapter Summary

A network is a connected collection of devices that can communicate with each other. Networks in homes, small businesses, or large enterprises allow users to share resources such as data and applications (e-mail, web access, messaging, collaboration, and databases), peripherals, storage devices, and backup devices. Networks carry data (or data packets) following rules and standards called protocols, each with its own specialized function. Networks can be evaluated in terms of both performance...

Characteristics of a Network

Many characteristics are commonly used to describe and compare various network designs. When you are determining how to build a network, each of these characteristics must be considered along with the applications that will be running on the network. The key to building the best network is to achieve a balance of these characteristics. Networks can be described and compared according to network performance and structure, as follows Speed Speed is a measure of how fast data is transmitted over...

Classes of Attack

Passive Passive attacks include traffic analysis, monitoring of unprotected communications, decrypting weakly encrypted traffic, and capturing authentication information such as passwords. Passive interception of network operations enables adversaries to see upcoming actions. Passive attacks result in the disclosure of information or data files to an attacker without the consent or knowledge of the user. Examples include the disclosure of personal information such as credit card numbers and...

Command Syntax Conventions

The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows Boldface indicates commands and keywords that are entered literally as shown. In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command). Italics indicate arguments for which you supply actual values. Vertical bars...

Common Physical Components of a Network

The physical components are the hardware devices that are interconnected to form a computer network. Depending on the size of the network, the number and size of these components varies, but most computer networks consist of the basic components shown in Figure 1-2. Figure 1-2 Common Network Components Figure 1-2 Common Network Components These are the four major categories of physical components in a computer network Personal computers (PCs) The PCs serve as endpoints in the network, sending...

Configuring Serial Encapsulation

You can use serial point-to-point connections to connect your LAN to your service provider WAN. You are likely to have serial point-to-point connections within your network, between your network and a service provider, or both. You need to know how to configure the serial ports for such connections. Circuit-switched WANs used to be the most common method of connecting remote sites. Because of the bandwidth requirements of modern applications, circuit-switching technology has been relegated to...

Constructing a Network Addressing Scheme

Subnetworks, also known as subnets, are very common in all but the smallest of network environments, segmenting the network into smaller divisions that have their own addresses. To create subnet addresses, some of the bits used for the host portion of an IP address are borrowed to create the subnet address. The following sections describe how subnets function and how they are computed. Network administrators often need to divide networks, especially large networks, into subnetworks, or subnets,...

Corporate and Government Sales

The publisher offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales, which may include electronic versions and or custom covers and content particular to your business, training goals, marketing focus, and branding interests. For more information, please contact U.S. Corporate and Government Sales 1-800-382-3419 corpsales pearsontechgroup.com For sales outside the United States, please contact International Sales international pearsoned.com

Cpu

Most of these components are hardware, as follows CPU This is the processor that runs the Cisco IOS and features like route processing. RAM This read write memory contains the software and data structures that enable the router to function. The principal software running in RAM is the Cisco IOS Software image and the running configuration. The RAM also contains the routing tables and packet buffers. RAM is volatile its memory contents will be lost when power is turned off. ROM This type of...

Crc

CRC errors can indicate a duplex mismatch or a malfunctioning Ethernet adapter in an attached device. The show interfaces command is used frequently while configuring and monitoring network devices. Switches use the MAC address tables to forward traffic between ports. These MAC tables include dynamic, permanent, and static addresses. To view the MAC address table, use the show mac-address-table command, as shown in Example 2-3. Example 2-3 show...

D

De-encapsulation, 38 encapsulation, 36-37 data link layer, 35 host-to-host communication, 86 LLC sublayer, 109 MAC sublayer, 109 WAN access standards, 350, 354 connectivity options, 355 data rates for WLANs, 224, 226 debug commands, 452-455 decimal numbering system, 247 converting to binary, 250-251 de-encapsulation, 36, 38 default gateway, 98 default routes, 242 default static routes, configuring, 378 from external sources, 153-154 hubs, 141 network map, creating, 432-433 repeaters, 141 DHCP...

D D

The IEEE divides the OSI data link layer into two separate sublayers Logical link control (LLC) Transitions up to the network layer MAC Transitions down to the physical layer LLC Sublayer The IEEE created the LLC sublayer to allow part of the data link layer to function independently from existing technologies. This layer provides versatility in services to the network layer protocols that are above it, while communicating effectively with the variety of MAC and Layer 1 technologies below it....

Data

Layer 3 192.168.3.1 Layer 2 0800 0222 2222 Layer 3 192.168.3.2 Layer 2 0800 0222 1111 As with the example in Chapter 1, Building a Simple Network, Address Resolution Protocol (ARP) does not have an entry in its MAC address table, so it must place the packet in the parking lot until it uses ARP to resolve the Layer 3 logical IP address to the Layer 2 physical MAC address. This is shown in Figure 2-6. Layer 2 ARP, do you have a mapping for 192.168.3.2 ARP Is...

Data Communications Process

All communications on a network originate at a source and are sent to a destination. A networking protocol using all or some of the layers listed in the OSI reference model move data between devices. Recall that Layer 7 is the part of the protocol that communicates with the application, and Layer 1 is the part of a protocol that communicates with the media. A data frame is able to travel across a computer network because of the layers of the protocol. The process of moving data from one device...

Dce

Data Terminal Equipment User Device with Interface Connecting to the WAN Link Data Circuit-Terminating Equipment End of the WAN Provider Side of the Communication Facility Your CPE, in this case a router, is the DTE. The data DCE, commonly a modem or a DSU CSU, is the device that converts the user data from the DTE into a form acceptable to the WAN service provider. The synchronous serial port on the router is configured as DTE or DCE (except EIA TIA-530, which is DTE only) depending on the...

Dedication

Becky, as the years go by, I love you more. Thank you for your support and understanding. Katie, your work ethic has always amazed me. As you prepare to move into the next phase of your life, remember your goals and keep working hard and you can achieve anything. Logan, you have never believed there was anything you couldn't do. Keep that drive and spirit and there will be no limit to what you can accomplish. Cameron, you have a keen sense of curiosity that...

DeEncapsulation

When the remote device receives a sequence of bits, the physical layer at the remote device passes the bits to the data link layer for manipulation. The data link layer performs the following process, referred to as de-encapsulation Step 1 It checks the data link trailer (the FCS) to see if the data is in error. Step 2 If the data is in error, it is discarded. Step 3 If the data is not in error, the data link layer reads and interprets the control information in the data link header. Step 4 It...

Des

Suspending and Resuming a Telnet Session After connecting to a remote device, you might want to access a local device without terminating the Telnet session. Telnet allows temporary suspension and resumption of a remote session. Figure 4-52 shows a Telnet session from Router A to Router B. The key sequence shown is entered to suspend the session. The output indicates that the Telnet session has been suspended. Figure 4-52 Suspending a Telnet Session

Dhcpack

After the DHCP server receives the DHCPREQUEST message, it acknowledges the request with a DHCPACK message, thus completing the initialization process. Using a Cisco Router as a DHCP Server Cisco routers running Cisco IOS Software provide full support for a router to be a DHCP server. The Cisco IOS DHCP server is a full DHCP server implementation that assigns and manages IP addresses from specified address pools within the router to DHCP clients. You can configure a DHCP server to assign...

Dhcpoffer

A DHCP server that receives a DHCPDISCOVER message can respond with a DHCPOFFER message, which contains initial configuration information for the client. For example, the DHCP server provides the requested IP address. The subnet mask and default gateway are specified in the options field, subnet mask, and router options, respectively. Other common options in the DHCPOFFER message include IP address lease time, renewal time, domain name server, and NetBIOS Name Service (Microsoft Windows...

Discovering Neighbors on the Network

Most network devices, by definition, do not work in isolation. A Cisco device frequently has other Cisco devices as neighbors on the network, and being able to obtain information about those other devices is important to assist with network design decisions, troubleshooting, and completing equipment changes. The following sections describe how to gather information about the Cisco devices in a network and use that information to create a map of the network environment. The Cisco Discovery...

Dly

Delay of the interface, in microseconds. Reliability of the interface as a fraction of 255 (255 255 is 100 percent reliability), calculated as an exponential average over 5 minutes. Load on the interface as a fraction of 255 (255 255 is completely saturated), calculated as an exponential average over 5 minutes. Encapsulation method assigned to an interface. Indicates whether keepalives are set. Type of Address Resolution Protocol (ARP) assigned. Number of hours, minutes, and seconds since the...

Dst Ip 19216831

Layer 3 192.168.3.1 Layer 2 0800 0222 2222 Layer 3 192.168.3.2 Layer 2 0800 0222 1111 Layer 3 192.168.3.2 Layer 2 0800 0222 1111 The data exchange continues until the application stops sending data. In the host-to-host packet delivery example, the host was able to use ARP to map a destination's MAC address to the destination's IP address. However, this option is available only if the two hosts are on the same network. If the two hosts are on different networks, the sending host must send the...

Dst

When host 192.168.3.2 receives the frame, it notes the broadcast address and strips the Layer 2 encapsulation. Figure 1-68 shows this operation. Layer 2 I just got a frame with a broadcast MAC, so I'll process it. The protocol ID indicates that it belongs to ARP. Let me strip the Layer 2 header and send it to ARP.

Dst Mac

Layer 3 192.168.3.1 Layer 2 0800 0222 2222 Layer 3 192.168.3.2 Layer 2 0800 0222 1111 When the switch receives the frame, it needs to forward it out the proper port. However, in this example, neither the source nor the destination MAC address is in the switch's MAC address table. The switch can learn the port mapping for the source host by reading and learning the source MAC address in the frame, so the switch will add the source MAC address, and the port it learned it on, to the port mapping...

Dynamic

SwitchX Dynamic addresses are source MAC addresses that are learned by the switch by reading the source MAC address in a frame as it is received by the switch port, and then dropped if they are not refreshed and aged out. The switch provides dynamic addressing by learning the source MAC address of each frame that it receives on each port, and then adding the source MAC address and its associated port number to the MAC address table. As stations are added or removed from the network, the switch...

E

EGPs (exterior gateway protocols), 396 EIRP (Effective Isotropic Radiated Power), calculating, 212 encapsulation, 36-37, 68 Enterprise Mode, 220 branch office, 4 home office, 4 main office, 4 speed requirements, 187 WLANs, client features, 227-228 environmental security threats, 175, 306 ESA (Extended Service Area), 224 ESS (Extended Service Set), 223 Ethernet addressing, 113 collision domains, 142 collisions, 141-142 frames, 111-112 configuring, 185-187 LANs, 104-108, 140 connecting to,...

E1

Each wire is identified with the network address. This value is not assigned, but it is assumed. A value of 0 means this network or the wire itself' (for example, 172.16.0.0). This is the information used by the router to identify each network. The routing table contains entries for network or wire addresses it usually does not contain any information about hosts. As soon as the network portion is determined by the classification, you can determine the total number of hosts on the network by...

Employees

Find Open Networks Use Them to Gain Free Internet Access View Sensitive WLAN Info and Even Break into WLANs Plug Consumer-Grade APs Gateways into Company Ethernet Ports to Create Own WLANs War driving originally meant using a cellular scanning device to find cell phone numbers to exploit. War driving now also means driving around with a laptop and an 802.11b g client card to find an 802.11b g system to exploit. Most wireless devices sold today are WLAN-ready. End users often do not change...

Enabling RIP

While static routes provide a method for giving the router information about where networks are located so that they can route packets, they are not scalable. For that information you need to use a dynamic routing protocol. While a lot of different routing protocols exist, the Routing Information Protocol (RIP), which is a distance vector routing protocol, is one of the most enduring of all routing protocols. RIP is a relatively old, but still commonly used, interior gateway protocol created...

Enabling Static Routing

Routing is the process of determining where to send data packets destined for addresses outside the local network. Routers gather and maintain routing information to enable the transmission and receipt of such data packets. Conceptually, routing information takes the form of entries in a routing table, with one entry for each identified route. You can statically (manually) configure the entries in the routing table, or the router can use a routing protocol to create and maintain the routing...

Encapsulation

As indicated in the previous section, encapsulation on a data network is similar to the process of sending that mug. However, instead of sending a coffee mug to a friend, you send information from an application from one device to another. The information sent on a network is referred to as data or data packets. Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the data moves down through the layers of the OSI reference model, each OSI layer...

Exploring the Functions of Networking

To understand how networks function, you need to become familiar with the basic elements of a network. This chapter explains networks by introducing fundamental computer and network concepts and the characteristics, functions, benefits, metrics, and attributes used to describe network features and performance. This chapter also introduces the Open System Interconnection (OSI) reference model, data communications terms and concepts, and the TCP IP protocol, which serves as the de facto standard...

Exploring the Functions of Routing

Routing is the process that forwards data packets between networks or subnetworks using a Layer 3 device a router or gateway. The routing process uses network routing tables, protocols, and algorithms to determine the most efficient path for forwarding the IP packet. Routers greatly expand the scalability of networks by terminating Layer 2 collisions and broadcast domains. Understanding how routers function will help you understand the broader topic of how networks are connected and how data is...

Exploring the Packet Delivery Process

The previous sections discussed the elements that govern host-to-host communications. You also need to understand how these elements interact. This section covers host-to-host communications by providing a graphic representation. Layer 1 defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Some common examples are Ethernet segments and serial links like Frame Relay and T1. Repeaters...

Exploring Wireless Networking

Wireless networking technology has developed like most new technologies business needs drive technology developments, which in turn drive new business needs, which in turn drive new technology developments. To keep this cycle from spinning out of control, several organizations have stepped forward to establish WLAN standards and certifications. This lesson describes the trends and standards that impact WLAN development. Productivity is no longer restricted to a fixed work location or a defined...

Extended Star Topology

A common deployment of an extended-star topology is in a hierarchical design such as a WAN or an Enterprise or a Campus LAN. Figure 1-10 shows the topology of an extended star. The problem with the pure extended-star topology is that if the central node point fails, large portions of the network can become isolated. For this reason, most extended-star topologies employ a redundant connection to a separate set of connection devices to prevent isolation in the event of a device failure.

Fcs

SOF Start-of-Frame Delimiter FCS Frame Check Sequence SOF Start-of-Frame Delimiter FCS Frame Check Sequence Preamble This field consists of 7 bytes of alternating 1s and 0s, which synchronize the signals of the communicating computers. Start-of-frame (SOF) delimiter This field contains bits that signal the receiving computer that the transmission of the actual frame is about to start and that any data following is part of the packet. Destination address This field contains the address of the...

Features

This book features actual router and switch output to aid in the discussion of the configuration of these devices. Many examples, illustrations, and notes are spread throughout the text. In addition, you can find many references to standards, documents, books, and websites to help you understand networking concepts. At the end of each chapter, your comprehension and knowledge are tested by review questions prepared by a certified Cisco Systems instructor. NOTE The operating system used in this...

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 email at...

Foreword

Cisco Certification Self-Study Guides are excellent self-study resources for networking professionals to maintain and increase internetworking skills and to prepare for Cisco Career Certification exams. Cisco Career Certifications are recognized worldwide and provide valuable, measurable rewards to networking professionals and their employers. Cisco Press exam certification guides and preparation materials offer exceptional and flexible access to the knowledge and information required to stay...

Full Mesh Topology

The full-mesh topology connects all devices (or nodes) to one another for redundancy and fault tolerance. Implementing a full-mesh topology is expensive and difficult. This method is the most resistant to failures because the failure of any single link does not affect reachability in the network. Figure 1-13 shows the connections in a full-mesh topology. Figure 1-13 Full-Mesh Topology Figure 1-13 shows the connections in a full-mesh topology. Figure 1-13 Full-Mesh Topology

Gh

Protocol, 386 help system (CLI), 156-159 history of Internet, 361-362 home office, 4 hop count, 243 hosts per subnet, calculating, 255-257 host-to-host communication, 84-87 verifying with shop ip arp command, 302-304 Layer 3 addressing, 295 packet delivery, 89-98, 295-301 connectivity, verifying, 99-102 default gateway, 98 switching, packet delivery process, 144-151 host-to-host communications model, 42-43 hubs, 141

H

Network Address (Host Bits All os) The decimal numbers that fill the first two octets in a Class B network address are assigned. The last two octets contain 0s because those 16 bits are for host numbers and are used for devices that are attached to the network. The IP address in the example (172.16.0.0) is reserved for the network address it is never used as an address for any device that is attached to it. An example of an IP address for a device on the 172.16.0.0 network would be 172.16.16.1....

Hdlc

Flag Address Control Data FCS Flag Flag Address Control Proprietary Data FCS Flag PPP originally emerged as an encapsulation protocol for transporting IP traffic over point-to-point links. PPP also established a standard for the assignment and management of IP addresses, asynchronous (start and stop bit) and bit-oriented synchronous encapsulation, network protocol multiplexing, link configuration, link quality testing, error detection, and option negotiation for such capabilities as network...

I

I could have walked to Finance by now. Collisions are by-products of the CSMA CD method used by Ethernet. In a shared-bandwidth Ethernet network, when using hubs, many devices will share the same physical segment. Despite listening first, before they transmit, to see whether the media is free, multiple stations might still transmit simultaneously. If two or more stations on a shared media segment do transmit at the same time, a collision results, and the frames are destroyed. When the sending...

1

Suppose that a host named London sends a frame to a host named Rome. London resides on network segment A, and Rome resides on network segment B. Redundant connections between switches and hosts are provided to ensure continual operations in the case of a segment failure. For the example shown in Figure 2-24, it is assumed that none of the switches have learned host B's address.

Dyp

Authority), 396 IBSS (Independent Basic Service Set), 222 IEEE (Institute for Electrical and Electronic Engineers), 108, 211 standards, comparing, 213-214 IGPs (interior gateway protocols), 396 images, managing on Cisco IOS Software, 445-446, 448 implementing CDP, 428 WLANs, 227 infrastructure mode (802.11), 223 inside global address overloading, 367-368 inside global addresses, 364 inside local addresses, 364 inside source address translation, 366-367 insider attacks, 27 interactive...

Fvg

To display address conflicts found by a DHCP server when addresses are offered to the client, use the show ip dhcp conflict command in user EXEC or privileged EXEC mode The server uses ping to detect conflicts. The client uses Gratuitous Address Resolution Protocol (ARP) to detect clients. If an address conflict is detected, the address is removed from the pool and the address is not assigned until an administrator resolves the conflict. Example 4-17 displays the detection method and detection...

Hap

Closing connection to 10.3.3.2 confirm Closes the Current Session Opened by You Closes a Session Opened by a Remote Device You can close a Telnet session on a Cisco network device by using one of the following methods From a remote device, by using the exit or logout command to log out from the console session and return the session to the local device From the local device, by using the disconnect command (when there are multiple sessions) or the disconnect session session number command to...

Implementing a WLAN

Implementing a WLAN involves more than selecting the desired standard and selecting a security mechanism. Access point placement can have more effect on throughput than standards. You need to understand how the efficiency of a WLAN is affected by such issues as topology, distance, and access point location. Upon completing this lesson, you will be able to describe the factors affecting the implementation of a WLAN. Figure 3-8 shows the original standard-defined 802.11 topologies workgroup (ad...

Info

Figure 1-31 shows how the bits in the first octet identify the address class. The router uses the first bits to identify how many bits it must match to interpret the network portion of the address (based on the standard address class). Table 1-1 lists the characteristics of Class A, B, and C addresses that address network devices. Range of network numbers 1.0.0.0 to 126.0.0.0. Range of network numbers 128.0.0.0 to 191.255.0.0. Range of network numbers 192.0.0.0 to 223.255.255.0. Number of...

Interpreting a Network Diagram

When designing and describing a computer network, you use a drawing or diagram to describe the physical components and how they are interconnected. The network diagram uses common symbols to capture information related to the network for planning, reference, and troubleshooting purposes. The amount of information and the details of that information differ from organization to organization. The network topology is commonly represented by a series of lines and icons. Figure 1-3 shows a typical...

IP Network Addressing

Just as you use addresses to identify the specific locations of homes and businesses so that mail can reach them efficiently, you use IP addresses to identify the location of specific devices on a network so that data can be sent correctly to those locations. IP addressing has various aspects, including the calculations for constructing an IP address, the classes of IP addresses designated for specific routing purposes, and public versus private IP addresses. Learning how IP addresses are...

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Layer 3 192.168.3.2 Layer 2 0800 0222 1111 After the sender receives the ARP response, it populates its own ARP cache and then moves the packet out of the parking lot and places the appropriate Layer 2 destination MAC address on the frame for delivery, as shown in Figure 2-12. As the data is sent to the switch, the switch recognizes that the destination MAC address of the receiver is connected out a particular port, and it sends only the frame out that port to the receiver, where it is received...

Jam Jam Jam Jam Jam

Stations on a CSMA CD LAN can access the network at any time. Before sending data, CSMA CD stations listen to the network to determine whether it is already in use. If it is, the CSMA CD stations wait. If the network is not in use, the stations transmit. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously (see the figure). In this case, both transmissions are damaged, and the stations must retransmit at some later time. CSMA CD stations must...

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Addressing, 113 collision domains, 142 collisions, 141-142 connecting to, 115-116, 118-120, frames, 111-112 MAC addresses, 113 physical redundancy, 187, 189-190 segments, distance limitations, 140 segments, extending, 141 standards, 108-109 versus WANs, 348 latency, 80 Layer 1. See physical layer Layer 2. See data link layer Layer 2 addressing, 295 verifying with show ip arp command, 302-304 Layer 3. See network layer Layer 3 addressing, 295 Layer 4. See transport layer Layer 5. See session...

L3 L2

L3 192.168.4.2 L2 0800 0222 1111 The user has programmed the IP address of 192.168.3.2 as the default gateway. Host 192.168.3.1 sends out the ARP request, and it is received by the router. Figure 4-34 shows the PC sending out an ARP request. Figure 4-34 ARP Request for Router Parking Lot ARP The ARP request will say that I am 192.168.3.1. Who is 192.168.3.2

LAN Connections

In addition to connecting multiple devices in a network, the networks themselves can be connected. In fact, the Internet is a collection of connected networks. The concept of connected networks is a common communication infrastructure in large organizations. Connecting networks with diverse devices, architectures, and protocols requires more sophisticated components than simple local-area networks (LAN). Routers are the devices used in this more complex networking environment, and a suite of...

Layer 4 The Transport Layer

The transport layer segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. For example, business users in large corporations often transfer large files from field locations to a corporate site. Reliable delivery of the files is important, so the transport layer breaks down large files into smaller segments that are less likely to incur transmission problems. The boundary between the transport layer and the session layer can be...

Layer 5 The Session Layer

The session layer establishes, manages, and terminates sessions between two communicating hosts. It provides its services to the presentation layer. The session layer also synchronizes dialogue between the presentation layers of the two hosts and manages their data exchange. For example, web servers have many users, so many communication processes are open at a given time. Therefore, keeping track of which user communicates on which path is important. In addition to session regulation, the...

Li

The switch learns the port mapping for the source host by reading the source MAC address in the ARP broadcast reply frame. So the switch adds this new source MAC address and the port that it learned it on to the port-mapping table or MAC address table. In this case 0800 0222 1111 port 2. Because the new destination MAC address being replied to was previously added to the switch's MAC table, the switch can now forward the reply frame back out port 1, and only out port 1, because it knows what...

Logical Topologies

The logical topology of a network refers to the logical paths that the signals use to travel from one point on the network to another that is, the way in which data accesses the network media and transmits packets across it. The physical and logical topologies of a network can be the same. For example, in a network physically shaped as a linear bus, the data travels along the length of the cable. Therefore, the network has both a physical bus topology and a logical bus topology. On the other...

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The traceroute command shows the routes that the packets take between network devices. A device, such as a router or switch, sends out a sequence of User Datagram Protocol (UDP) datagrams to an invalid port address at the remote host. Three datagrams are sent, each with a Time to Live (TTL) field value set to 1. The TTL value of 1 causes the datagram to time out as soon as it hits the first router in the path. The router then responds with an Internet Control Message Protocol (ICMP) Time...

Managing Cisco Devices

Carefully managing Cisco IOS images and configuration files reduces device downtime and maintains best practices. Cisco IOS image files contain the Cisco IOS Software required for a Cisco device to operate, and the device configuration files contain a set of user-defined configuration commands that customize the functionality of a Cisco device. The Cisco IOS File System (Cisco IFS) feature provides a single interface to all the file systems that a router uses. This topic describes the file...

Managing Cisco Router Startup and Configuration

When a Cisco router boots, it performs a series of steps in a particular order. At several points during the process, the router makes a decision about the next step to take. Knowledge of the boot sequence can be of great help when troubleshooting a Cisco router and also when adjusting its configuration. The following sections describe each step in the router boot sequence. Stages of the Router Power-On Boot Sequence When a router boots, it performs a series of steps performing tests, finding...

Maximizing the Benefits of Switching

As devices are added to LANs to accommodate more users, and more bandwidth is required by more networked software applications, maintaining an acceptable level of network performance becomes an increasing challenge. There are a number of ways to enhance switched Ethernet LANs to meet the demands of users for performance and availability. Microsegmentation eliminates the possibility of collisions on the network segment, providing a number of benefits in increasing network performance. Figure...

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NAT (Network Address Translation), 54, 356, 363-364 inside global address overloading, 367-368 inside source address translation, 366-367 verifying configuration, 373 network access layer (TCP IP model), 41 network devices, configuring, 152-153 from external sources, 153-154 network diagrams, interpreting, 6-7 network ID, 51 network layer, 35 network map, creating with CDP, 432-433 networks, 5-6 topology, 12-15, 17-19 resource-sharing functions, 7-8 user applications, 9 interactive...

Need for Network Security

In the past, hackers were highly skilled programmers who understood the intricacies of computer communications and how to exploit vulnerabilities. Today almost anyone can become a hacker by downloading tools from the Internet. These sophisticated attack tools and generally open networks have generated an increased need for network security and dynamic security policies. The easiest way to protect a network from an outside attack is to close it off completely from the outside world. A closed...

Network Environment Management

The network staff is responsible for ensuring that the underlying communications infrastructure is capable of supporting business objectives and associated applications. Network staff is also responsible for managing each device on the network according to best industry practices and for reducing device downtime. This chapter describes commands and processes to determine network operational status, gather information about remote devices, and manage Cisco IOS images, configuration files, and...

Network User Applications

The key to utilizing multiple resources on a data network is having applications that are aware of these communication mechanisms. Although many applications are available for users in a network environment, some applications are common to nearly all users. The most common network user applications include the following E-mail E-mail is a valuable application for most network users. Users can communicate information (messages and files) electronically in a timely manner, to not only other users...

Nvram

The Cisco IFS feature provides a single interface to all the file systems that a Cisco router Network file systems TFTP, Remote Copy Protocol (RCP), and FTP (This lesson only discusses commands used to transfer Cisco IOS images and configuration files to and from a TFTP server.) Any other endpoint for reading or writing data (such as NVRAM, the running configuration in RAM, and so on) One key feature of the Cisco IFS is the use of the URL convention to specify files on Table 6-2 contains some...

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Comparing to TCP IP protocol suite, 41-42 data communications process de-encapsulation, 38 encapsulation, 36-37 data link layer, 35 LLC sublayer, 109 MAC sublayer, 109 host-to-host communication, 84-87 packet delivery process, 89-102 host-to-host communications model, 42-43 layered approach to troubleshooting, 192 network layer, 35 peer-to-peer communication, 39-40 physical layer, 36 presentation layer, 34 session layer, 35 transport layer, 35, 39 WAN access standards, 350 data link layer,...

OSI Reference Model

The OSI reference model is the primary model for network communications. The early development of LANs, MANs, and WANs was chaotic in many ways. The early 1980s saw tremendous increases in the number and sizes of networks. As companies realized that they could save money and gain productivity by using networking technology, they added networks and expanded existing networks as rapidly as new network technologies and products were introduced. By the mid-1980s, companies began to experience...

Oui

The address that is on the NIC is the MAC address, often referred to as the burned-in address (BIA), and some vendors allow the modification of this address to meet local needs. A 48-bit Ethernet MAC address has two components 24-bit Organizational Unique Identifier (OUI) The letter O identifies the manufacturer of the NIC card. The IEEE regulates the assignment of OUI numbers. Within the OUI, the two following bits have meaning only when used in the destination address Broadcast or multicast...