Cisco Router Configuration

Cisco Router Configuration

by Allan Leinwand, Bruce Pinsky

Paperback(Older Edition)

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Basic Router Configuration will provide sample scenarios for novices using the Cisco IOS for configuration, operation, and maintenance of internetworking devices. The is book will focus on the three most popular networking protocols used today: TCP/IP, IPX, and AppleTalk. This book covers the commonly used IOS commands and the most popular options, making clear the use of the IOS for a variety of users and internetworking configuration. This will be accomplished through the use of copious examples, illustrations, and Cisco IOS configuration output. An entire sample internetwork will be built throughout the text to help illustrate the concepts being described.
  • First book available concentrating on Cisco s Internetwork Operating System (IOS)
  • Shows Cisco s IOS output with explanations
  • Contains examples of 3 complete network setups

Product Details

ISBN-13: 9781578700226
Publisher: Cisco Press
Publication date: 04/10/1998
Edition description: Older Edition
Pages: 436
Product dimensions: 7.40(w) x 9.08(h) x 1.08(d)

Read an Excerpt

1. Getting Started in Internetworking

This chapter helps you start learning about internetworking. Understanding this complex topic is the first step toward understanding the Cisco Internetwork Operating System (IOS). The IOS provides the intelligence that Cisco products require to perform their various internetworking tasks. The IOS is an operating system with a proprietary user interface, command set, configuration syntax, and so on. The IOS is to Cisco devices as Windows 2000 is to IBM-compatible personal computers. The IOS runs on all the Cisco products discussed in this text.

We encourage you to have a firm grasp of the internetworking principles surveyed in this chapter before you attempt to understand the complexities of the Cisco IOS. Internetworking is a term used to describe the collection of protocols and devices that interoperate on data networks. This chapter gives you the basic understanding of the subject; it is not meant to give you comprehensive coverage of the subject (which could take multiple books to cover completely). If you need a more extensive introduction to internetworking, a few good texts are cited in the "References" section at the end of this chapter.

When you finish this chapter, you should be comfortable with the OSI networking model and have a basic understanding of how bridges, switches, routers, and access servers work. Chapter 2, "The Basics of Device Configuration," introduces you to the basics of configuring a Cisco device.

The OSI Reference Model

The Open System Interconnection (OSI) reference model is a principle of internetworking that you must understand to appreciate the way Cisco devices operate. The OSIreference model is a seven-layer architectural model developed by the International Organization for Standardization (ISO) and the International Telecommunications Union-Telecommunications (ITU-T). It is used universally to help individuals understand network functionality. The OSI reference model adds structure to the many complexities involved in the development of communications software. The development of communications software involves many tasks, including dealing with multiple types of applications, transmission strategies, and physical network properties. Without structure, communications software might be difficult to write, change, and support.

ISO is an international organization founded to promote cooperation in technological developments, particularly in the field of communications. ITU-T, on the other hand, is a global organization that drafts standards for all areas of international analog and digital communications. ITU-T deals with telecommunications standards.

The OSI reference model is divided into seven distinct layers. Each layer performs a specific, distinct task that helps communications systems operate. The layer operates according to a set of rules, which is called a protocol. In addition to following the rules of the protocol, each layer provides a set of services to the other layers in the model. The seven layers of the OSI reference model are the application, presentation, session, transport, network, data link, and physical layers, as shown in Figure I-1. In the following sections, we briefly review each layer, starting with the application layer.

The Application Layer

The application layer provides the interface to the communications system, which the user sees. Many common applications are used today in an internetwork environment, such as web browsers, File Transfer Protocol (FTP) clients, and electronic mail. An example of application layer communication is a web browser downloading a document from a web server. The web browser and server are peer applications on the application layer that communicate directly with each other for the retrieval of the document. They are unaware of the six lower layers of the OSI reference model, which are working to produce the necessary communications.

The Presentation Layer

The presentation layer deals with the syntax of data as it is being transferred between two communicating applications. The presentation layer provides a mechanism to convey the desired presentation of data between applications. Many people infer that the look and feel of the environment of a computer desktop, such as the way all the applications look and interact uniformly on a computer by Apple Computer, Inc., is an example of a presentation layer. In fact, this is not a presentation layer, but a series of applications using a common programmer's interface. One common presentation layer in use today is Abstract Syntax Notation One (ASN.1), which is used by protocols such as the Simple Network Management Protocol (SNMP) to represent the structure of objects in network management databases.

The Session Layer

The session layer allows two applications to synchronize their communications and exchange data. This layer breaks the communication between two systems into dialogue units and provides major and minor synchronization points during that communication. For example, a large distributed database transaction between multiple systems might use session layer protocols to ensure that the transaction is progressing at the same rate on each system.

The Transport Layer

The transport layer, Layer 4, is responsible for the transfer of data between two session layer entities. Multiple classes of transport layer protocols exist, from those that provide basic transfer mechanisms (such as unreliable services) to those that ensure that the sequence of data arriving at the destination is in the proper order, that multiplex multiple streams of data, that provide a flow control mechanism, and that ensure reliability.

As you will see in the next section, some network layer protocols, called connectionless protocols, do not guarantee that the data arrives at the destination in the order in which it was sent by the source. Some transport layers handle this by sequencing the data properly before handing it to the session layer. Multiplexing of data means that the transport layer can simultaneously handle multiple streams of data (which could be from different applications) between two systems. Flow control is a mechanism that the transport layer can use to regulate the amount of data sent from the source to the destination. Transport layer protocols often add reliability to a session by having the destination system send acknowledgments back to the source system as it receives data.

In this text, we discuss the three commonly used transport protocols: the Transmission Control Protocol (TCP) that is used on the Internet, Novell's Streams Packet Exchange (SPX), and Apple's AppleTalk Transport Protocol (ATP).

The Network Layer

The network layer, which routes data from one system to another, provides addressing for use on the internetwork. The Internet Protocol (IP) defines the global addressing for the Internet; Novell defines proprietary addressing for the Internetwork Packet Exchange (IPX), its client/server architecture; and Apple's AppleTalk uses the Datagram Delivery Protocol (DDP) and proprietary addressing for communicating between its machines on the network layer. In later chapters, we explore the specifics of each of these types of network layer addresses.

Network layer protocols route data from the source to the destination and fall into one of two classes, connection-oriented or connectionless. Connection-oriented network layers route data in a manner similar to using a telephone. They begin communicating by placing a call or establishing a route from the source to the destination. They send data down the given route sequentially and then end the call or close the communication. Connectionless network protocols, which send data that has complete addressing information in each packet, operate like the postal system. Each letter, or packet, has a source and a destination address. Each intermediate post office, or network device, reads this addressing and makes a separate decision on how to route the data. The letter, or data, continues from one intermediate device to another until it reaches the destination. Connectionless network protocols do not guarantee that packets arrive at the destination in the same order in which they were sent. Transport protocols are responsible for the sequencing of the data into the proper order for connectionless network protocols.

The Data Link Layer

Layer 2, the data link layer, provides the connection from the physical network to the network layer, thereby enabling the reliable flow of data across the network. Ethernet, Fast Ethernet, Token Ring, Frame Relay, and Asynchronous Transfer Mode (ATM) are all Layer 2 protocols that are commonly used today. As you will see throughout this text, data link layer addressing is different from network layer addressing. Data link layer addresses are unique to each data link logical segment, while network layer addressing is used throughout the internetwork.

The Physical Layer

The first layer of the OSI reference model is the physical layer. The physical layer is concerned with the physical, electrical, and mechanical interfaces between two systems. The physical layer defines the properties of the network medium, such as fiber, twisted-pair copper, coaxial copper, satellite, and so on. Standard network interface types found on the physical layer include V35, RS-232C, RJ-11, RJ-45, AUI, and BNC connectors.

The Data Exchange Process

These seven layers all work together to provide a communications system. The communication occurs when a protocol on one system, which is located at a given layer of the model, communicates directly with its corresponding layer on another system. The application layer of a source system logically communicates with the application layer of the destination system. The presentation layer of the source system passes data to the presentation layer of the destination system. This communication occurs at each of the seven layers of the model.

This logical communication between corresponding layers of the protocol stack does not involve many different physical connections between the two communications systems. The information each protocol wants to send is encapsulated in the layer of protocol information beneath it. The encapsulation process produces a set of data called a packet.

Starting at the source, as shown in Figure 1-2, the application-specific data is encapsulated in the presentation layer information. To the presentation layer, the application data is generic data being presented. The presentation layer hands its data to the session layer, which attempts to keep the session synchronized. The session layer passes data to the transport layer, which transports the data from the source system to the destination system. The network layer adds routing and addressing information to the packet and passes it to the data link layer. The data link layer provides framing for the packet and the connection to the physical layer.

At Layer 1, as shown in the figure, the physical layer sends the data as bits across a medium, such as copper or fiber. The packet then traverses the destination network from Layer 1 to Layer 7. Each device along the way reads only the information necessary to get the data from the source to the destination. Each protocol de-encapsulates the packet data and reads the information sent by the corresponding layer on the source system.

As an example, consider what occurs when you open a Web page using a Web browser. Given a URL, such as, your browser asks the TCP to open a reliable connection to the Web server that is located at (Many applications that use TCP skip the presentation and session layers, as we do in this example.) TCP then requests the network layer (IP) to route a packet from the source IP address to the destination IP address. The data link layer takes this IP packet and encapsulates it again for the particular type of data link leaving the source system, such as Ethernet. The physical layer carries the signal from the source system to the next system en route to the destination, such as a router...

Table of Contents

Chapter 1Getting Started in Internetworking2
The OSI Reference Model3
The Application Layer4
The Presentation Layer4
The Session Layer5
The Transport Layer5
The Network Layer5
The Data Link Layer6
The Physical Layer6
The Data Exchange Process7
Types of Internetworking Devices9
Bridges and Switches9
Access Servers13
An Internetwork Example13
Chapter 2The Basics of Device Configuration18
Preliminary Configuration Steps19
The Console Port20
The System Configuration Dialog21
The Help System25
Nonprivileged and Privileged Modes28
Memory Configuration Issues29
Device Configuration Memory29
IOS Flash Memory31
User Configuration Mode36
Configuration Commands38
Removing Configuration Commands41
Default Configuration Commands41
Merging and Superseding of Configuration Commands42
Chapter 3The Basics of Device Interfaces46
Basic Interface Configuration47
The show interfaces Command48
The encapsulation Command49
The shutdown Command49
The description Command50
Local-Area Network Technologies51
Ethernet and IEEE 802.352
Fast Ethernet54
Fast Ethernet and Ethernet Interface Configuration Subcommands55
Gigabit Ethernet55
Token Ring56
Token Ring Interface Configuration Subcommands58
Fiber Distributed Data Interface58
Wide-Area Network and Dialup Network Technologies60
High-Level Data Link Control62
Point-to-Point Protocol63
X.25 Interface Configuration Subcommands65
Frame Relay67
Frame Relay Interface Configuration Subcommands68
Asynchronous Transfer Mode70
ATM Interface Configuration Subcommands72
Digital Subscriber Line73
Integrated Services Digital Network75
ISDN Interface Configuration Subcommands77
Chapter 4TCP/IP Basics82
TCP/IP Addressing83
Address Structure83
Configuring IP Addresses89
LAN Interface Configuration92
WAN Interface Configuration96
Verifying IP Address Configuration102
IP Routing Configuration104
Configuring IP Routing Commands105
Verifying IP Routing Configuration116
Configuring IP Routing Protocols118
Configuring the Routing Information Protocol123
Configuring the Cisco Interior Gateway Routing Protocol125
Configuring the Open Shortest Path First Protocol126
Configuring the Cisco IP Enhanced Interior Gateway Routing Protocol129
Configuring the Border Gateway Protocol130
Managing Dynamic Routing Protocol Information136
Viewing Dynamic Routing Protocol Information139
Configuring IP Filtering via Access Lists142
Defining the Access List143
Applying the Access List146
Configuring Basic IP Dialup Services148
Configuring Asynchronous Dialup149
ISDN Dialup158
Verifying IP Connectivity and Troubleshooting163
Configuring Other IP Options170
Configuring Domain Name Services170
IP Broadcast Forwarding172
Dynamic Address Assignment with IOS DHCP Server175
IP Redundancy with the Hot Standby Router Protocol183
Chapter 5Apple Talk Basics196
AppleTalk Addressing and Address Structure199
Configuring AppleTalk Addresses203
LAN Interface Configuration204
WAN Interface Configuration207
Verifying AppleTalk Address Configuration210
AppleTalk Routing Configuration211
Configuring AppleTalk Routing Commands211
Configuring Static Routing212
Verifying AppleTalk Routing Configuration213
Configuring AppleTalk Routing Protocols215
Configuring AppleTalk RTMP215
Configuring AppleTalk EIGRP216
Configuring AppleTalk Filtering via Access Lists219
Defining Access Lists219
Applying Access Lists221
Configuring Basic AppleTalk Dialup Services223
Verifying AppleTalk Connectivity and Troubleshooting225
Chapter 6IPX Basics236
IPX Addressing and Address Structure238
Configuring IPX Addresses240
LAN Interface Configuration240
WAN Interface Configuration243
Verifying IPX Address Configuration245
IPX Routing Configuration246
Configuring IPX Routing Commands247
Configuring Static Routing247
Verifying IPX Routing Configuration248
Configuring IPX Routing Protocols248
SAP Filters250
Configuring IPX RIP252
Configuring NLSP254
Configuring IPX EIGRP255
Configuring IPX Filtering via Access Lists256
Defining Access Lists256
Applying Access Lists257
Configuring Basic IPX Dialup Services258
Verifying IPX Connectivity and Troubleshooting259
Configuring IPX Type 20 Packet Forwarding262
Chapter 7Basic Administrative and Management Issues266
Basic Access Control267
Connecting to a Virtual Terminal Using Telnet and SSH267
Enabling the SSH Server268
Verifying SSH Configuration269
Securing the Console Port and Virtual Terminals269
Enabling AAA272
RADIUS and TACACS+ Compared275
Basic Attack Prevention275
TCP Intercept275
Unicast Reverse Path Forwarding276
Basic Network Management280
Basic Time Control285
Manual Time and Date Configuration286
Network Time Protocol287
Simple Network Time Protocol289
Chapter 8Comprehensive IOS Configuration for the ZIP Network294
The Kuala-Lumpur Router295
The SF-1 Router298
The SF-2 Router299
The SF-Core-1 Router301
The SF-Core-2 Router304
The San-Jose Router306
The Seoul-1 Router308
The Seoul-2 Router312
The Singapore Router313
The SingISDN Access Server315
The Sing2511 Access Server318

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