Cisco Systems CCNA 2 User Manual

This document is exclusive property of Cisco Systems, Inc. Permission is granted to print and copy this document for noncommercial distribution and exclusive use by instructors in the CCNA 2: Routers and Routing Basics course as part of an official Cisco Networking Academy Program.

I. Welcome

Welcome to the CCNA 2 version 3.1 Instructor Guide. Cisco Worldwide Education (WWE) has developed this guide to provide a helpful resource for instructors. This introduction will emphasize four themes:

• Student-centered, instructor-facilitated model

• One size does not fit all

• Hands-on, skills-based learning

• Global community of educators

Student-Centered, Instructor-Facilitated

The CCNA curriculum has not been designed as a standalone e-learning or distance-learning course. The teaching and learning model of the Cisco Networking Academy® Program is based on instructor facilitation. The Learner Model: Academy Student diagram shows the emphasis that WWE puts on the learner. The model begins with the prior knowledge of students. The instructor guides learning events, which are built from a variety of resources, to help the students achieve their desired comprehension of networking.

One Size Does Not Fit All

The Cisco Networking Academy Program serves hundreds of thousands of students in almost 150 countries. Students range from early teens to mature adults and from advanced middle school students to undergraduate engineering students.

One curriculum cannot fit the needs of all students. WWE relies on local instructors to make the program work and to help their students achieve the learning goals of the program. There are three fixed reference points for each program that provide flexibility for the instructors:

• The mission of WWE to educate and train

• The requirements of the CCNA certification exam

• The hands-on skills that help prepare students for the industry and further

education

The WWE policy allows instructors to "add anything, but subtract nothing" from the curriculum. WWE supports in-class differentiation, which is used to provide additional support for students who need it and additional challenges for advanced students. WWE also allows instructors to decide how much time to spend on various topics. Some topics can be skimmed, while others may need to be emphasized for different audiences. The local instructor must decide how to balance the need for hands-on labs with the realities of the local student-to-equipment ratio and time schedule. This Guide can be used to facilitate the preparation of lesson plans and presentations. Instructors are encouraged to research and use external sources to develop additional labs and exercises.

Core TIs have been highlighted for emphasis to assist the instructor in course and lesson planning. These are not the only TIs that need to be taught. Many core TIs will only make sense after the preceding TIs have been reviewed. It may be useful to have a map of the core TIs, which contain the most important knowledge and skills for success in the CCNA program.

The assessment process is multifaceted and flexible. A wide variety of assessment options exist to provide feedback to students and document their learning. The Academy assessment model is a blend of formative and summative assessments that include online and hands-on, skills-based exams.

Hands-On, Skills-Based

The core of the CCNA 2 experience is the sequence of hands-on labs. Labs are designated as either essential or optional. Essential labs include information that is fundamental to the CCNA Academy student experience. This information will help students prepare for the certification exam, succeed in job situations, and develop their cognitive abilities. In CCNA 2, students will learn about the following elements of basic router configuration:

• Hostnames, banners, and passwords

• Interface configuration

• IOS file system

• Static routes and dynamic routing (RIP version 1 and IGRP)

• Standard and extended access-list configuration and placement

• show, debug, ping, trace, and telnet commands to verify and troubleshoot

Global Community

WWE instructors are members of a global community of educators. There are over 10,000 instructors that teach the same eight CCNA and CCNP courses in the program. Instructors should take advantage of the diversity and skills of this community through their Regional Academies, Cisco Academy Training Centers (CATCs), the Cisco Academy Connection (CAC), or through other forums. WWE is committed to the improvement of the curriculum, assessment model, and instructional resources such as this guide. Please submit any feedback through CAC. Check CAC for new releases of instructional materials.

Guide Overview:

Section II provides a scope and sequence overview of the course. Section III summarizes the most important learning objectives, target indicators, and labs, and offers teaching suggestions and background information. Section IV provides a case study related to network design, implementation, and troubleshooting. Instructors can also devise their own case studies. Section V includes four appendices:

• Cisco online tools and utilities

• CCNA assessment guidelines

• Evidence-centered design of assessment tasks in the Networking Academy

program

• Instructional best practices

II. Course Overview

Target Audience

The target audience is anyone who desires a practical and technical introduction to the field of networking. This includes high school, community college, and lifelong-learning students who are interested in careers as network technicians, network engineers, network administrators, and network help-desk staff.

Prerequisites

The successful completion of this course requires the following:

• Reading age level of 13 or higher

• Successful completion of CCNA 1

The following prerequisites are beneficial, but not required:

• Prior experience with computer hardware and command line interfaces

• Background in computer programming

Course Description

CCNA 2: Routers and Routing Basics is the second of four CCNA courses that lead to the Cisco Certified Network Associate (CCNA) designation. CCNA 2 focuses on initial router configuration, Cisco IOS Software management, routing protocol configuration, TCP/IP, and access control lists (ACLs). Students will learn how to configure a router, manage Cisco IOS software, configure routing protocols on routers, and set access lists to control access to routers.

Course Objectives

The CCNA certification indicates knowledge of networking for the small office, home office (SOHO) market and the ability to work in small businesses or organizations that use networks with fewer than 100 nodes. A CCNA-certified individual can perform the following tasks:

• Install and configure Cisco switches and routers in multiprotocol internetworks that use LAN and WAN interfaces

• Provide Level 1 troubleshooting service

• Improve network performance and security

• Perform entry-level tasks in the planning, design, installation, operation, and

troubleshooting of Ethernet and TCP/IP Networks

Students must successfully complete the CCNA 2 course before they can achieve CCNA certification.

Upon completion of this course, students will be able to perform tasks related to the following:

• Routers and their roles in WANs

• Cisco IOS Software Management

• Router configuration

• Router file management

• RIP and IGRP routing protocols

• TCP/IP error and control messages

• Router troubleshooting

• Intermediate TCP

• Access control lists

Lab Requirements

Please refer to the CCNA equipment bundle spreadsheets on the Cisco Academy Connection.

Certification Alignment

The curriculum is aligned with the following Cisco Internet Learning Solution Group (ILSG) courses:

• CCNA (Cisco Certified Network Associate)

• INTRO (Introduction to Cisco Networking Technologies)

The Course 2 claims state that students will be able to complete the following tasks:

• Identify the key characteristics of common wide-area network (WAN) configurations and technologies, and differentiate between these and common LAN technologies

• Describe the role of a router in a WAN

• Describe the purpose and operations of the router Internet Operating System

(IOS)

• Establish communication between a terminal device and the router IOS, and use IOS for system analysis, configuration, and repair

• Identify the major internal and external components of a router, and describe the associated functionality

• Connect router Fast Ethernet, serial WAN, and console ports

• Perform, save, and test an initial configuration on a router

• Configure additional administrative functionality on a router

• Use embedded data-link layer functionality to perform network neighbor discovery

and analysis from the router console

• Use embedded Layer 3 through Layer 7 protocols to establish, test, suspend, or disconnect connectivity to remote devices from the router console

• Identify the stages of the router boot-up sequence and show how the configuration register and boot system commands modify that sequence

• Manage system image and device configuration files

• Describe the operation of the Internet Control Message Protocol (ICMP) and

identify the reasons, types, and format of associated error and control messages

• Identify, configure, and verify the use of static and default routes

• Evaluate the characteristics of routing protocols

• Identify, analyze, and show how to rectify inherent problems associated with

distance vector routing protocols

• Configure, verify, analyze, and troubleshoot simple distance vector routing protocols

• Use commands incorporated within IOS to analyze and rectify network problems

• Describe the operation of the major transport layer protocols and the interaction

and carriage of application layer data

• Identify the application of packet control through the use of various access control lists

• Analyze, configure, implement, verify, and rectify access control lists within a router configuration

Course Overview

The course has been designed for 70 contact hours. Approximately 35 hours will be designated to lab activities and 35 hours will be designated to curriculum content. A case study on routing is required. The format and timing should be determined by the Local Academy.

The following changes have taken place since CCNA version 2.x:

• More emphasis on router configuration early in semester

• More efficient presentation and practice of IOS

• IGRP moved from CCNA 3 to CCNA 2

• Access lists moved from CCNA 3 to CCNA 2

• Revisions to TCP/IP coverage

• More focus on routing tables

• Case study is required with format and timing determined by the Local Academy

• More interactive flash activities

• Sequence of over 40 e-Labs

• Lab focus on two-router labs

III. Teaching Guide for Each TI

Nomenclature

The CCNA curriculum uses the following hierarchy:

• Course

• Module

• Learning objective (LO)

• Target indicator (TI)

For example, 3.2.5 references Module 3, LO 2, and TI 5. The following terms are commonly used to describe the curriculum, instructional materials, and assessments in WWE and Cisco documentation:

• Certification-level claims

High-level statements about what a CCNA-certified person should know and be able to do. These claims are measured through certification exams.

• Course A subset of a curriculum which is a collection of chapters to be offered as a

scheduled course

• Course-level claims Medium-level statements about what a person who completes the CCNA 2 course

should know and be able to do.

• Core TI

The TIs that apply most directly to the claims and learning objectives. Instructors should not skip over these TIs or move through them quickly.

• Curriculum A predefined or dynamic path of learning events with an end goal such as

certification or the acquisition of required job skills and knowledge.

• Hands-on skills There is some overlap between hands-on skills and claims. These statements

emphasize hands-on, lab-based learning.

• Module Logical groupings that comprise a course. Modules contain multiple lessons or

LOs. Modules are also referred to as chapters.

• Learning objective (LO) A statement that establishes a measurable behavioral outcome. LOs are used to

organize content and to indicate how the acquisition of skills and knowledge will be measured. LOs are also referred to as terminal objectives or RLOs.

• Lesson A set of TIs, or enabling objectives, that are grouped together and presented in a

coherent format to meet an LO, or terminal objective. Lessons emphasize the role of the instructor. Learning objectives emphasize the role of the students.

• Module caution Suggestions related to areas where difficulties may be encountered. These are

especially important for syllabus development, lesson planning, and pacing.

• Optional lab A lab that is for practice, enrichment, or differentiation.

• Essential lab A lab that is fundamental to the course.

• Reusable Learning Object (RLO) This is a Cisco Instructional Design term. RLOs typically consist of five to nine

RIOs. In this guide, RLOs are equivalent to lessons or learning objectives.

• Reusable Information Object (RIO) This is a Cisco Instructional Design term. In this guide, RIOs are equivalent to

target indicators.

• Target indicator (TI) TIs are also referred to as enabling objectives or RIOs. TIs typically consist of a

text frame with graphics and several media content items.

Module 1: WANs and Routers

Overview

When teaching Module 1, show the students how router configuration relates to the Internet, which is a global internetwork made possible by routers. Students will learn the difference between WANs and LANs, and will identify WAN connections, encapsulations, and protocols.

Module 1 Caution

WANs will be taught in detail in CCNA 4. In CCNA 2, it is important to teach students the fundamental basics of WANs and roles that routers play in the WAN connection. Inform the students that the serial interfaces will be used to simulate the DCE to DTE WAN connection. Do not spend too much time on this module.

Students who complete this module should be able to:

• Identify organizations responsible for WAN standards

• Explain the difference between WANs and LANs and the types of addresses they

use

• Describe the role of a router in a WAN

• Identify internal components of a router and describe their functions

• Describe the physical characteristics of a router

• Identify common ports on a router

• Connect Ethernet, serial WAN, and console ports

1.1 WANs

Essential labs: None Optional labs: None Core TIs: All Optional TIs: none Course-level claim: Students can identify the important characteristics of common WAN

configurations and technologies, differentiate between these and common LAN technologies, and describe the role of a router in a WAN.

Certification-level claim: Students can evaluate the important characteristics of WANs and implement simple WAN protocols.

Hands-on skills: none

1.1.1 Introduction to WANs

WANs differ from LANs in several ways:

• LANs connect workstations, peripherals, terminals, and other devices in a single building or several buildings that are located next to each other, and WANs connect large geographic areas.

• LANs connect devices and WANs connect data connections across a broad geographic area.

WANs operate at the physical and data-link layers of the OSI model. Devices used in a WAN are routers, switches, modems, and communication servers. The following topics are relevant to this TI:

• Discuss the various carriers and devices available for WAN connections.

• Show students what routers in a WAN look like.

• Explain what routers do.

Figure 3 is an important figure to review. Best instructional practices for this TI include online study sessions with study guides, group work, and mini-lectures. This TI provides essential background information for the CCNA exam.

1.1.2 Introduction to routers in a WAN

Routers and computers have four basic common components:

• CPU

• Bus

• Memory

• Interfaces

However, the main purpose of a router is to route, not to compute. The main components of the router are as follows:

• RAM

• NVRAM

• Flash

• ROM

• Interfaces

The following topics should be covered in this TI:

• Discuss the similarities of computers and routers such as the software they use.

• Explain the components of the router and what each component contains.

• Open a router and let the students examine the inside. Point out the main

components.

• Explain that just as a computer cannot work without an operating system and software, a router cannot work without an operating system and configurations.

1.1.3 Router LANs and WANs

Routers function in both LANs and WANs. They are primarily used in WANs. Explain that routers have both LAN and WAN interfaces. Students should be able to identify the differences. The two main functions of a router are to select the best path and to forward packets to the correct outgoing interfaces.

Networking models are useful because they facilitate modularity, flexibility, and adaptability. Like the OSI model, the three-layer design model is an abstract picture of a network. Models may be difficult to comprehend because the exact composition of each layer varies from network to network.

Explain that each layer of a three-layer design model may include a router, a switch, a link, or some combination of these. Some networks may combine the function of two layers into a single device or may omit a layer entirely. The three-layer design model consists of the following:

• The core layer forwards packets as quickly as possible.

• The distribution layer provides a boundary by using filters to limit what gets to the

core.

• The access layer feeds traffic into the network and controls entry into the network.

1.1.4 Role of Routers in a WAN

There are several encapsulations associated with serial lines:

• HDLC

• Frame Relay

• PPP

• SDLC

• SLIP

• LAPB

Some of the most common WAN technologies are as follows:

• POTS

• ISDN

• X.25

• Frame Relay

• ATM

• T1, T3, E1, and E3

• DSL

• SONET

Ask students to briefly explain each of the WAN technologies and discuss the differences between technologies and encapsulations. They will be covered in detail in CCNA 4.

It is important to encourage student interest and enthusiasm in this TI. The world of WAN technologies is briefly introduced. Many students will be familiar with one or more of the technologies used. Many of these topics will be covered in CCNA 4 and students should be encouraged to do additional research on one of these technologies and present it to the class.

1.1.5 Academy approach to hands-on labs

In the Networking Academy lab, all the networks are connected with a serial or Ethernet cable. This allows the students to see and touch all of the equipment. In a real network, the routers would not be in one physical location. In the Networking Academy lab, the serial cables are connected back-to-back. However, in the real world the cables would be connected through a CSU or DCE device.

Discuss the differences between real networking environments and the router lab setup. Help the students visualize the components between the V.35 connectors. If they can understand this picture, then they will realize that they are working with a complete WAN minus the carrier services.

Each student should build a complete topology and then take it apart and let the next student do the lab. These labs are a review of the cabling labs in CCNA 1. This may be one of the last opportunities students have to cable a network, so do not miss this opportunity to make sure students complete the CCNA 2 Lab setup. This is a good place to introduce troubleshooting and the Layer 1 issues that occur in CCNA 2. It is also a fairly simple and fun activity.

1.2 Routers

Essential Labs: 1.2.5, 1.2.6, and 1.2.7 Optional Labs: None Core TIs: All Optional TIs: none Course- Level Claim: Students can properly connect router Fast Ethernet, Serial WAN, and

console ports. Certification-Level Claim: Students can describe the components of network devices. They

can also identify the major internal and external components of a router and describe the associated functionality.

Hands-on skills: none

1.2.1 Introduction to WANs

This section overviews the physical aspect of a router. The physical layer is always studied first in networking topics. The student will be able to identify internal components of the router and describe their functions, describe the physical characteristics of the router, identify common ports on a router, and properly connect FastEthernet, Serial WAN, and console ports.

The components in a router are essentially the same as those in a computer. In fact, a router can be thought of as a computer designed for the special purpose of routing. While the exact architecture of the router varies in different router series, this section will introduce the major internal components. The figures show the internal components of some of the Cisco router models.

Ask students the following questions:

• What are the common components of a router?

• What is NVRAM used for?

1.2.2 Router physical characteristics

It is not necessary to know the location of the physical components inside the router to understand how to use the router. The exact components used and their locations vary in different router models.

Ask students the following questions:

• What are the different types of RAM used by a router?

• Can the RAM be upgraded in a router?

1.2.3 Router external connections

The three basic types of connections on a router are LAN interfaces, WAN interfaces, and management ports. LAN interfaces allow the router segment network boundaries within a LAN and reduce broadcast traffic within a LAN. WAN connections are provided through a service provider which connects two or more distant site through the Internet or PSTN. The LAN and WAN connections provide network connections through which frames are passed. The management port provides an ASCII or text-based connection for the configuration and troubleshooting of the router.

Ask students the following questions:

• What are the three basic types of connections on a router?

• What is the console connection used for?

1.2.4 Management port connections

The management ports are asynchronous serial ports. They are the console port and the auxiliary port. Not all routers have an auxiliary port. These serial ports are not designed as networking ports. To prepare for initial startup and configuration, attach an RS-232 ASCII terminal or a computer that emulates an ACSII terminal to the system console port.

It is essential for students to understand the difference between network interfaces and nonnetwork interfaces. The instructor may need to talk about the differences extensively.

Discuss the following topics:

• The network ports use network encapsulation frames while the non-network ports are bit and byte oriented.

• There is no addressing involved in the serial management ports.

• The serial interface for management is asynchronous and the serial WAN interface

is synchronous.

Ask students the following questions:

• Which port is preferred for troubleshooting and why?

• Do all routers have an auxiliary port?

1.2.5 Console Port Connections

The console port is a management port used to provide out-of-band access to a router. It is used for the initial configuration of the router, monitoring, and disaster recovery procedures.

Students may not be familiar with the term out-of-band. Out-of-band refers to the fact that the management control communications use a different path or channel than the data communications.

Ask students the following questions:

• What type of terminal emulation must the PC or terminal support?

• What are the steps to connect the PC to a router?

1.2.6 Connecting Router LAN interfaces

In most LAN environments, an Ethernet or FastEthernet interface is used to connect the router to the LAN. The router is a host that connects to the LAN through a hub or a switch. A straightthrough cable is used to make this connection. The correct interface must be used.

If the wrong interface is connected, the router or other networking devices may be damaged. This is generally not true within LAN interfaces. However, if LAN interfaces are connected to some form of WAN interface such as ISDN, damage can occur. The students should be taught to be observant and careful whenever connections are made.

Ask students the following questions:

• What type of cable is used to connect from the router Ethernet interface to a hub or switch?

• What type of cable is used to connect from the router Ethernet interface to a router Ethernet interface?

1.2.7 Connecting WAN interfaces

There are many forms of WAN connections. A WAN uses many different types of technology to make data connections across a broad geographic area. WAN services are usually leased from service providers. The WAN connection types include leased line, circuit switched, and packet switched.

Many of the WAN interfaces use the same physical interfaces but different pinouts and electrical characteristics. This difference in electrical characteristics could potentially cause damage if the wrong connections were made. Again, the students should be taught to be observant and careful when they make any connections.

Ask students to perform the following tasks:

• List the physical layer standards that Cisco routers support.

• List the different types of WAN connections.

Module 1 Summary

Before students move on to Module 2, they must be able to cable the lab setup, identify all external relevant ports, and identify internal router components.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 1 exam. Consider introducing formative assessments, where the instructor supervises the students as they work on the router setup. The use of formative assessments can be very valuable while students work through this router-intensive and IOS-intensive course.

Students should understand the following main points:

• WAN and LAN concepts

• Role of a router in WANs and LANs

• WAN protocols

• How to configure console connections

• The identification and description of the internal components of a router

• The physical characteristics of a router

• The common ports on a router

• How to connect router console, LAN, and WAN ports

Module 2: Introduction to Routers

Overview

Consider the prior knowledge of students when teaching Module 2. Some students may be familiar with command-line interfaces (CLIs). Students who have only used GUIs may not know how to use CLIs to interact with a computer. Students should experiment with CLIs to learn how to interact with a router.

Module 2 Caution

Students need to know what the IOS is and what it does. They also need to know the difference between the configuration file and the IOS. It is also important for students to feel comfortable when they enter into and move around in the CLI. Do not move too quickly through these labs. If students are uncomfortable with the CLI, they will have difficulties with more complex labs.

Students who complete this module should be able to perform the following tasks:

• Describe the purpose of the IOS

• Describe the basic operation of the IOS

• Identify various IOS features

• Identify the methods to establish a command-line interface (CLI) session with the

router

• Move between the user command executive (EXEC) and privileged EXEC modes

• Establish a HyperTerminal session on a router

• Log into a router

• Use the help feature in the command-line interface

• Troubleshoot command errors

2.1 Operating Cisco IOS Software

Essential Labs: None Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can describe the purpose and fundamental operation of the

router IOS. Certification-Level Claim: Students can establish communication between a terminal device

and the router IOS and use it for system analysis, configuration, and repairs.

Hands-on skills: none

2.1.1 The purpose of Cisco IOS software

In this TI, students will be introduced to the fundamentals of the Cisco Internet Operating System (IOS). Student will learn about the show version command, which helps users gain information about the Cisco IOS. The IOS command line interface is introduced in another lesson, so there is no need to focus on the show command in this TI.

A router and switch cannot function without an operating system. Cisco IOS is the installed software in all Cisco routers and Catalyst switches.

A computer needs an operating system such as Windows or UNIX. Discuss how the hardware cannot function without this software. Make sure the students understand the role of the IOS.

2.1.2 Router user interface

Cisco IOS software uses a command-line interface (CLI) as its console environment. The CLI is accessible through several methods:

• Console port

• Auxiliary port

• Telnet session

Students should know the difference between these methods. They should also be comfortable with the term CLI.

2.1.3 Router user interface modes

The user EXEC mode allows a limited number of basic monitoring commands. This mode is often referred to as a view-only mode. The privileged EXEC mode provides access to all router commands. To enter the privileged mode from user mode the enable command must be entered. The privileged mode is used to access other modes to configure the router.

Students should be able to identify the router prompts. The user mode prompt is Router>. The privileged mode prompt is Router#.

2.1.4 Cisco IOS software features

Cisco IOS devices have three operating environments:

• ROM monitor

• Boot ROM

• Cisco IOS

ROM monitor is used to recover from system failures and recover a lost password. Boot ROM is used to modify the Cisco IOS image in flash. There is a limited subset of features in this mode. Normal operation of a router requires the full Cisco IOS image. Discuss the three operating environments. Students should be able to identify these environments. Students must be familiar with the IOS to control the router. Cisco technology is in the IOS, not in the hardware.

2.1.5 Operation of Cisco IOS software

There are numerous IOS images for different Cisco device models. Each devise uses a similar basic command structure for configuration. The configuration and troubleshooting skills acquired on a specific device will apply to a variety of products.

The naming convention for the different Cisco IOS Releases contains three parts:

• The platform on which the image runs

• The special capabilities and feature sets supported in the image

• Where the image runs and whether it has been zipped or compressed

One of the major constraints for the use of a new IOS image is compatibility with the router flash and RAM memory.

The students should also understand that the same IOS is used on the smallest to the largest Cisco products. This will assure students that the skills they develop on small Cisco routers can be applied to larger routers and switches.

Show students various naming conventions and identify the three parts of the naming convention. For example, in cpa25-cg-1, cpa25 is the Cisco Pro 2500 Router, cg is the feature capability such as communication server, remote-access server, or ISDN, and the 1 is the run location or compressed status.

Explain that it is important to install and maintain various IOS versions, especially newer versions with advanced features. Encourage the students to conduct research online at www.cisco.com for more information on how to obtain various IOS images.

2.2 Starting a Router

Essential Labs: 2.2.1, 2.2.4, and 2.2.9 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can describe the purpose and fundamental operation of the

router IOS Certification-Level Claim: Students can establish communication between a terminal device

and the router IOS and use it for system analysis, configuration, and repair

Hands-on skills: none

2.2.1 Initial startup of Cisco routers

This section teaches students about the startup process for a router. Students learn how to establish a HyperTerminal session and log into a router. Students will then be introduced to the help feature and enhanced editing commands.

When a Cisco router powers up, it performs a POST. This executes diagnostics from ROM on all hardware modules. After the POST, the following events occur as the router initializes:

• Bootstrap is loaded from ROM.

• IOS is loaded from flash, TFTP, or ROM.

• Config is loaded from NVRAM or TFTP into setup mode.

This section teaches students how to check the configuration during the boot process. Setup mode is intended to quickly install a router with minimal configuration. Discuss the initial startup of routers and explain why the IOS and configuration files can be loaded from several places.

2.2.2 Router LED indicators

Router LED indicators indicate the status of a router. If an interface is extremely busy, its LED will be on all the time. The green LED will be on after the router card initializes correctly.

Have the students view the LED indicators on the routers in the lab setup. Show them LEDs that work correctly and explain what they are. Make sure the students understand that the port status and link LEDs are the prime indicators of the physical layer status.

2.2.3 The initial router bootup

Bootup messages displayed by a router include messages such as “NVRAM invalid, possibly due to write erase”, which indicates that the router has not been configured or the backup configuration has been erased.

If a router does not boot up correctly, issue the show version command to examine the configuration register to see if it is booting.

Remind the students that the router is a special purpose computer. It has a boot sequence that is similar to a standard computer. The router must load the IOS from one of several sources. The router must also obtain a configuration file. If a configuration file is not available, the router will enter setup mode, which prompts the user for a basic router configuration. Make sure the students understand what the router needs as basic configuration information. This provides a lot of information about how the router works. It is very important for students to understand the difference between the IOS and the configuration file.

2.2.4 Establish a console session

To establish a HyperTerminal Console session, students should complete the following steps:

1. Connect the terminal with an RJ-45-to-RJ-45 rollover cable and an RJ-45-to-DB-9 or RJ-45-to-DB-25 adapter

2. Configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control

Instruct the students to connect the cables from the router to the PC and to connect with the HyperTerminal program. To configure a router, a connection must be established between the PC and a router. Make sure students understand that this is how routers need to be configured initially, but it is not the only way to configure a router.

2.2.5 Router login

There are two levels of access to commands in a router:

• User EXEC mode

• Privileged EXEC mode

The user EXEC mode is a view-only mode. Enter privileged EXEC mode with the enable command from the User prompt. Other modes can be accessed from privileged mode to configure a router. The students should have a lot of practice with hands-on activities in the lab setup. It is important for students to understand the various modes to be able to accurately configure a router. It is not necessary to memorize all commands. Students must understand each mode so they can make the configurations from the correct locations.

2.2.6 Keyboard help in the router CLI

At the user mode prompt, a question mark (?) should be typed to display a list of commands available in the router. From user mode, the enable command will switch the router into the privileged mode. If a question mark (?) is entered from the privileged mode prompt, many more commands are listed as available commands to use in the router. Students should briefly review the types of commands in each mode. There is no need to memorize all of the commands.

The context-sensitive help is one of the most useful features of the IOS. Teach the student that the question mark (?) is extremely helpful in the router.

To demonstrate the help feature, instruct students to set the clock without telling them which commands to use. The question mark (?) will guide students through the process.

2.2.7 Enhanced editing commands

Enhanced editing commands are on by default. To disable enhanced editing mode, the terminal no editing command can be used at the privileged mode prompt.

The editing command set provides a horizontal scrolling feature for commands that extend beyond a single line. When the cursor reaches the right margin, the command line shifts ten spaces to the left. The first ten characters of the line cannot be seen, but a user can scroll back to check the syntax. It is represented by a dollar sign ($).

Some of the editing commands are as follows:

• Ctrl-A moves to the beginning of the command line.

• Ctrl-B moves back one character.

• Ctrl-E moves to the end of the command line.

• Ctrl-F moves forward one character.

• Ctrl-Z moves back out of configuration mode.

• Esc and then B moves back one word.

• Esc and then F moves forward one word.

The syntax of IOS commands can be complex. Keyboard editing features can be used to correct text that has been entered. When a router is being configured, repetitive command statements, typing errors that need to be fixed, and commands that need to be reused may be encountered. Questions about the Ctrl key and Esc key sequences will probably appear on the CCNA exam.

2.2.8 Router command history

The user interface provides a history of commands that have been entered. This feature can be used to recall long or complex commands. The command history feature can be used to complete the following tasks:

• Set the command history buffer size

• Recall commands

• Disable the command history feature

By default, the command history records ten command lines in the history buffer. To recall commands, press Ctrl-P or the Up Arrow key to recall repeated commands. Press Ctrl-N or the Down Arrow key to recall more recent commands in the history. The Ctrl-P and Ctrl-N features are also likely to be tested on the CCNA exam.

The syntax of IOS commands can be complex. The feature used to recall commands can help students save time when they program or troubleshoot a router.

2.2.9 Troubleshooting command line errors

This troubleshooting lab allows students to log into the router and access various modes. Demonstrate the use of the question mark (?) as a helpful tool for students who do not know which command to enter.

Also demonstrate the use of the history command as a helpful tool for students to troubleshoot problems without retyping repeated commands.

2.2.10 The show version command

The show version command displays information about the Cisco IOS software version. This information includes the system image file name and the location from which it was booted. It also contains the configuration register and the boot-field setting. Explain that an important aspect of router and IOS maintenance is to know exactly which version of the IOS is being used.

Cisco has numerous major and minor IOS releases. There are many different versions and different features to meet the requirements of a network. Students should know that the show version command shows much more than just the version of the IOS. This is an important command. Explain to students is that this is the only command that can be used to examine the configuration register.

Module 2 Summary

Before students move on to Module 3, they must be able to interact with the router through a HyperTerminal session and the CLI.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 2 exam. Make sure students know how to access the command-line prompt. Formative assessments related to lab work are relevant to Module 2.

Students should understand the following main points:

• Understand the basic operation of IOS

• Identify various IOS features

• Identify methods to establish a CLI session with the router

• Use HyperTerminal to establish a CLI session

• Log into the router

• Use the help feature in the command line interface

• Use the enhanced editing commands

• Use the command history

• Troubleshoot command line errors

• Use the show version command

Module 3: Configuring a Router

Overview

When teaching Module 3, emphasize the empowerment that students will gain from the ability to configure routers and the importance of familiarity with the IOS through extensive practice. There are many tools available to teach IOS:

• The curriculum text and graphics are used to introduce command syntax and context.

• The online command references are integrated.

• CiscoPedia is the IOS command reference in the form of a Windows help file. All

CCNA and CCNP commands are included.

• Integrated e-Labs provide guided practice of command syntax.

• Standalone e-SIMs provide more open-ended practice of CCNA 2-level router

configuration.

• Hands-on labs are integrated PDF files that should be the core of the learning experience.

Module 3 Caution

Spend a lot of time on this module. Students have wanted to program routers since the first day of CCNA 1. This module presents the core skills that the students will use to build all Cisco device configurations. From this point in the CCNA 2 curriculum through the end of the CCNA 4 curriculum, students may be deprived of the opportunity to learn about the IOS if the student-to-equipment ratio is high. Only the local instructor can decide what mix of lab equipment, group work, creative rotations, lab access, remote access through NetLabs or other solutions, e-Labs, e-SIM, CiscoPedia, and other tools can be used to give students adequate opportunities to learn IOS.

After completing this module, students should be able to perform the following tasks:

• Name a router

• Set passwords

• Examine show commands

• Configure a serial interface

• Configure an Ethernet interface

• Make changes to a router

• Save changes to a router

• Configure an interface description

• Configure a message-of-the-day banner

• Configure host tables

• Understand the importance of backups and documentation

3.1 Configure a Router

Essential Labs: 3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.1.6, and 3.1.7 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can perform, save, and test an initial configuration on a router. Certification Level Claim: Students can perform an initial configuration on a router. Hands-on skills: none

3.1.1 CLI command modes

The students need to understand that the router does not know what routing to do until it is configured. This section will help students begin the configuration of a router.

To gain access to a router, a login is required. After login, there is a choice of modes. The modes interpret the commands that are typed and perform the operations. There are two EXEC modes:

• User EXEC mode

• Privileged EXEC mode

The first configuration mode is referred to as global configuration mode or global config. The following configuration modes are available in global configuration mode:

• Interface

• Subinterface

• Controller

• Map-list

• Map-class

• Line

• Router

Global configuration commands are used in a router to apply configuration statements that affect the entire system. Use the privileged EXEC command configure terminal to enter global configuration mode.

Explain that Cisco IOS is modal. Emphasize that in the CLI that there are different modes to accomplish different tasks. There are several advantages to this. One is that the commands are generally shorter because the object of the mode, i.e., the interface, or routing protocol, to

be changed does not need to be specified in the command. Another advantage is that only the parameters, or objects of the mode, i.e., the interface, or routing protocol, can be modified by the command. This helps prevent accidental configuration of the wrong object. There are shortcuts to show students at a later time:

• config t for configure terminal

• int fa0/0 for interface fastethernet 0/0

Students commonly enter the correct command at the incorrect prompt. If the students are unable to enter a command, check the mode. The prompt will be either Router(config)# or

Router(config-if)#.

Ask students the following questions:

• Which mode is the user in when first logging into the router?

• What mode is the user in after entering the enable command?

3.1.2 Configuring a router name

One of the first basic configuration tasks is to name a router. This task helps with network management and uniquely identifies each router within a network. Use global configuration mode to name a router. The name of a router is called the hostname and will be displayed as the system prompt. If a router is not named, then the system default will be “Router”.

Students need to understand that the name is an important part of the configuration process. Much of the configuration and troubleshooting will be performed remotely. Users will telnet into different routers. For practice, ask students to name the routers. When instructors are asked to help troubleshoot a lab, they can easily identify the different routers. The router name at the prompt confirms the student has completed this task. Students should also understand that names should be chosen to represent a location or a function. In many organizations, there are naming conventions to be followed.

Ask students the following questions:

• What is the default name of the router?

• In which mode can the user name the router?

• What is the command to name a router?

3.1.3 Configuring router passwords

Passwords can be used to secure a router and restrict access. Passwords can be established for virtual terminal lines and the console line. The privileged EXEC mode may also have a password. From global configuration mode use the enable password command to restrict access to the privileged mode. The line configuration mode can be used to establish a login password on the console terminal. Use the command line vty 0 4 to establish a login password on incoming Telnet sessions.

Discuss the differences between the various passwords. Students need to understand when each password is used. If students ask if user ids and passwords can be used instead of just passwords, the answer is that they can, but that is beyond the scope of this course.

Ask students the following questions:

• What is the command to set the enable password?

• What is the command to set the telnet password?

• What is the command to set the console password?

3.1.4 Examining the show commands

There are many show commands, which are used to examine the contents of files in the router and for troubleshooting. From each mode in the router, the show ? command can be used to see all the available options. Some of the show command options are as follows:

• show interfaces

• show controllers serial

• show clock

• show hosts

• show users

• show history

• show flash

• show version

• show ARP

• show protocol

• show startup-configuration

• show running-configuration

Students may want to use the show running-config command as their primary troubleshooting tool. This is not a good habit. It is probably the quickest way to find problems in the simple configurations used in this course. However, that is not true in most situations. Students should learn to use the show running-config command to confirm suspected problems. Some CLI shortcuts to show students in the future are as follows:

• sh int fa0/0 for show interface fastethernet 0/0

• sh run for show running-configuration

• sh run int fa0/0 for show running-configuration fastethernet 0/0

Ask students the following questions:

• Which command will show the configuration file in NVRAM?

• Which command will show the configuration file in RAM?

3.1.5 Configuring a serial interface

A serial interface can be configured from the console or through a virtual terminal line. By default, Cisco routers are DTE devices but they can be configured as DCE devices. To configure a serial interface follow these steps:

1. Enter global configuration mode.

2. Enter interface mode.

3. Specify the interface address and subnet mask.

4. Set the DCE clock rate. Skip this step on DTE.

5. Turn on the interface. There are two important items in this TI. The first item is that setting a clock rate is not a normal configuration item. It is only done to

simulate a WAN. The clock is normally provided by the DCE equipment such as a CSU. The curriculum shows the command entered as clock rate, but on some Cisco routers the command can be entered as clockrate. Both will result in the same running configuration.

The second item is that interfaces are shutdown by default and must be enabled with the no shutdown command. The shutdown command will turn off an interface. Instruct students to check for interfaces that are shutdown when troubleshooting the student labs. This can be checked by typing show interface serial 0/0 or show run int serial 0/0 for the interface serial 0/0.

Ask students the following questions:

• What command turns on an interface?

• What command turns off an interface?

• What command is entered on an interface at the DCE end of the cable?

3.1.6 Making configuration changes

To verify changes, use the show running-config command. This command will display the current configuration. If the intended variables are not displayed, the environment can be corrected in the following ways:

• Issue the no form of a configuration command.

• Restart the system and reload the original configuration file from NVRAM.

• Remove the startup configuration file with the erase startup-config

command.

• Restart the router and enter setup mode.

To save the configuration variables to the startup configuration file in NVRAM, enter the following command at the privileged EXEC prompt:

Router#copy running-config startup-config

Students must understand that any changes that are made to the configuration will occur immediately. These changes are made to the running configuration. Students must also realize that configuration changes need to be saved to the startup configuration. If they are not, then they will be lost when the router is restarted. Students should shut down interfaces during configuration and enable the interface after the configuration changes are completed.

Ask students the following questions:

• Which command will erase the configuration file in NVRAM?

• Which command will erase the configuration file in RAM?

• Which command will copy the RAM to NVRAM?

• Which command will copy the NRAM to RAM?

3.1.7 Configuring an Ethernet interface

An Ethernet interface can be configured from the console or a virtual terminal line. By default, interfaces are disabled. Use the no shutdown command to enable an interface. Use the shutdown command to turn off an interface if it needs to be disabled for maintenance or troubleshooting. The following command is used to configure interface serial 0/0. The interface will change to up. Both ends of the serial cable need to be configured for the interface to stay in an up state:

rt1(config)#interface serial 0/0

rt1(config-if)#ip address 192.168.0.1 255.255.255.0

rt1(config-if)#no shutdown

00:20:46: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up

00:20:47: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up

rt1(config-if)#

3.2 Finishing the Configuration

Essential Labs: 3.2.3, 3.2.5, 3.2.7, and 3.2.9 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can configure additional administrative functionality on a router Certification-Level Claim: Students can configure a router for additional administrative

functionality.

Hands-on skills: none

3.2.1 Importance of configuration standards

This section introduces the importance of configuration standards. The following topics are covered:

• Configuration of interface descriptions

• Message-of-the day banners

• Configuration of host tables

• Backup configuration documentation

In many organizations, standards are either treated very seriously or there are no standards. It is important to develop standards for configuration files within an organization. These can be used to control of the number of configuration files that must be maintained, how the files are stored, and where the files are stored.

In organizations where standards are treated seriously, students need to understand that it is very important for the standards to be followed. In organizations where there are no standards, students can introduce standards to add value to the organization.

Students need to understand why standards are important and begin to apply them in the lab. Encourage students to create and use standards. Remember to simulate real-world environments in the classroom and lab.

A centralized support standard is necessary to manage a network. Configuration, security, performance, and other issues must be adequately addressed for the network to function properly. The creation of standards for network consistency helps reduce network complexity, the amount of unplanned downtime, and exposure to network impacting events. Emphasize that there should be a standard for everything and that each standard should be a written part of the documentation and procedures. These should include how configuration files are named, how interfaces are addressed, and the description used on interfaces.

The use of these standards is very important for troubleshooting. Explain to students that the same network associate will not always troubleshoot the network device. If the previous

associate did not have or follow standards, then the next associate will need to analyze how the device is supposed to be connected or configured. For example, if the headquarters router always has the lowest address in a subnet configured and the remote office uses the next address up, then there is no question about what the interface addresses should be. The interface description should provide information about the configuration, connection, and use of the interface.

3.2.2 Interface descriptions

The description of an interface should be used to identify important information such as a distant router, a circuit number, or a specific network segment. A description of an interface can help a network user remember specific information about the interface such as which network the interface services.

The description is a comment about the interface. Stress the importance of a standard type of description. Students will use small routers in a small topology and can get physical access to the routers. Since this is the extent of their experience, it is hard for them to understand how helpful interface descriptions are.

Ask the students to envision an environment with hundreds of routers, thousands of interfaces, and routers that are 1000 kilometers (621.4 miles) away. Tell the students that a customer from a branch office is unable to connect to headquarters. Ask students how they can verify that the interface is connected to the correct branch office before they change anything on the interface. There are several good answers such as ask the customer, refer to documentation, and use the show cdp neighbor command. The best answer is to look at the interface description with the show interface command.

Ask students the following questions:

• What is used on an interface to make a comment?

• Which type of information may be included in a description?

3.2.3 Configuring an interface description

To configure an interface description, enter global configuration mode. From global configuration mode, enter interface mode. Use the following steps:

1. Enter global configuration mode with the configure terminal command.

2. Enter a specific interface mode such as interface ethernet 0.

3. Enter the description command followed by the information to be displayed. For

example, XYZ network, Building 10.

4. Exit interface mode and return to global configuration mode by pressing Ctrl-Z. Save the configuration changes to NVRAM with the copy running-config startup-

config command. Important concepts for students to understand are that each description is for a particular

interface and the description is entered in interface configuration.

Ask students the following questions:

• Which configuration mode is used to enter the description?

• What are the commands to add a description to an interface?

3.2.4 Login banners

Students must realize that a login banner can be seen by anyone. This login banner should be a warning that users should not attempt to log in unless they are

authorized. A message such as “This is a secure system, authorized access only!” instructs unwanted intruders to beware. A login banner is a message that is displayed at login and can be used to convey messages that affect all network users such as system shutdowns. Make sure students understand that these banners should be warnings and not invitations.

Ask students the following questions:

• Who can see a login banner?

• What is an example of a good login banner?

• Where is the login banner displayed?

3.2.5 Configuring message-of-the-day (MOTD)

A message-of-the-day (MOTD) banner can be displayed on all connected terminals. Students must enter global configuration mode to configure a message-of-the-day banner. They should use the banner motd command, followed by a space and a delimiting character such as the pound sign (#). Next, students should add a message of the day followed by a space and the delimiting character again. Instruct students to follow these steps to display a message-of-theday:

1. Enter global configuration mode with the configure terminal command.

2. Enter the banner motd # message of the day # command.

3. Save changes with the copy running-config startup-config or copy run

start command.

3.2.6 Host name resolutions

Protocols such as Telnet use host names to identify network devices or hosts. Network devices such as routers must be able to associate host names with IP addresses to communicate with other IP devices.

Each unique IP address can have a host name associated with it. The Cisco IOS software maintains a cache of host name-to-address mappings for use by EXEC commands. A host name resolution is the process a computer system uses to associate a name with a network address.

Ask students the following questions:

• What is a host name is associated with?

• Can each unique IP address have a host name associated with it?

3.2.7 Configuring host tables

This is a simple process. Students need to understand that the host table provides local host resolution.

3.2.8 Configuration backup and documentation

The configuration of network devices determines the behavior of a network. The following tasks are used to manage device configurations:

• List and compare configuration files on devices

• Store configuration files on network servers

• Perform software installations and upgrades

Configuration files should be stored as backup files. Configuration files can be stored on a network server, on a TFTP server, or on a disk that is stored in a safe place. Configuration backup files and documentation should be stored in a safe place in case there is a need to recover these files later.

For example, the startup-configuration of a router can be stored in another place such as on a network server or on a TFTP server as a backup. If the router goes down, the stored file could be placed back on the router. This would minimize the down time.

Configuration management is an important aspect of network management. The backups of the configurations should be current and maintained in multiple locations. These backups should be available for maintenance and troubleshooting, but protected from unauthorized access. Configurations can be used by hackers to gain useful information about a network infrastructure.

Ask students the following questions:

• What is the purpose of configuration backup and documentation?

• Where can the configuration files be stored?

• What would minimize the down time of a router?

3.2.9 Backing up configuration files

A current copy of the configuration can be stored on a TFTP server. The copy runningconfig tftp command can be used to store the current configuration on a network TFTP

server. A router can be configured by loading the configuration file stored on one of the network servers. The configuration of a router can also be saved to a disk or hard drive by

capturing text in the router. If the file needs to be copied back to the router, it can be pasted into the router.

Ask students the following questions:

• What is the command used to copy RAM to NVRAM?

• What is the command used to copy NVRAM to RAM?

Module 3 Summary

Before students begin Module 4, they must be able to perform a basic router configuration in a limited amount of time and without assistance. Basic configuration includes hostnames, passwords, interfaces, and the ability to verify their work with show commands.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 3 exam. Formative assessments can also be conducted as students work on the routers to monitor how well a lab is performed.

This section summarized the main points in router configuration. The router has several modes:

• User EXEC mode

• Privileged EXEC mode

• Global configuration mode

• Other configuration modes

The CLI can be used to make changes to the configuration such as the following:

• Set the hostname

• Set passwords

• Configure interfaces

• Modify configurations

• Show configurations

Students should understand the following main points:

• Configuration standards are important elements in the ability of any organization to maintain an efficient network.

• Interface descriptions can include important information to help network administrators understand and troubleshoot their networks.

• Login banners and messages-of-the-day provide users with information when they log in to the router.

• Host name resolutions translate names to IP addresses to allow the router to quickly convert names to addresses.

• Configuration backup and documentation is extremely important to keep a network operating properly.

Module 4: Learning about Other Devices

Overview

Module 4 will introduce students to the Cisco Discovery Protocol (CDP). CDP is enabled by default on all Cisco devices. CDP allows devices such as Cisco routers to obtain information about directly connected routers, switches, and bridges. CDP functions at Layer 2 in the OSI model. It operates independently of Layer 3, which means that devices can gather information about other directly connected devices regardless of network layer protocol issues.

The first lesson will explain how CDP is used to acquire information about neighboring routers. Students should already know how use serial and Ethernet connections to physically connect routers. Students should also know how to use programs such as HyperTerminal and Telnet to perform router configuration tasks. Review these skills if necessary. Have students perform a standard lab-setup configuration as an optional skill review.

The second lesson will introduce students to the TCP/IP protocol Telnet. Telnet is a remote connection utility that allows network administrators to perform configuration and management tasks on routers and switches. Students will learn how to establish, manage, and terminate Telnet sessions with remote devices. Students should already be familiar with basic router setup and configuration. Students should possess basic router configuration skills and be able to physically connect the devices. Students will use embedded Layer 3 through Layer 7 protocols to establish, test, suspend, or disconnect connectivity to remote devices from the router console.

Module 4 Caution Most students do not understand that CDP and Telnet are powerful troubleshooting tools. At

this point, it is important to provide additional support for students who have not mastered Module 3. Cover this module extensively. Many of the next modules are lab intensive and time intensive.

Students who complete this module should be able to perform the following tasks:

• Enable and disable CDP

• Use the show cdp neighbors command

• Determine which neighboring devices are connected to which local interfaces

• Use CDP to gather network address information about neighboring devices

• Establish a Telnet connection

• Verify a Telnet connection

• Disconnect from a Telnet session

• Suspend a Telnet session

• Perform alternative connectivity tests

• Troubleshoot remote terminal connections

4.1 Discovering and Connecting to Neighbors

Essential Labs: 4.1.4 and 4.1.6 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can use embedded data-link layer functionality to perform

network neighbor discovery and analysis from the router console.

Hands-on skills: none

4.1.1 Introduction to CDP

CDP is a Cisco proprietary protocol that is used for Layer 2 troubleshooting and network documentation. CDP is used to acquire protocol and platform information from neighboring devices. It is enabled by default on Cisco devices and requires all media that is used to be Subnetwork Address Protocol (SNAP) enabled. Most media is SNAP enabled.

During the boot-up process, each Cisco device sends CDP advertisements to a multicast address to collect information from its neighbors. These advertisements are periodically repeated so that updated information can be gathered. CDP advertisements are also used by the receiving devices to learn about the sender. CDP information is dynamic. It is constantly updated through periodic advertisements. Reporting devices provide a Time-to-Live (TTL) value for the data.

CDP operates at Layer 2 and is upper layer independent. Review Figure 1 with students. CDP allows each Cisco device to collect information from its neighbors regardless of the Layer 3 protocols the devices are configured to use. Discuss the following characteristics of CDP:

• CDP runs on all Cisco devices such as routers, switches, and bridges.

• CDP is Cisco proprietary.

• CDP is upper-layer independent.

• CDP information is exchanged only by directly-connected neighbors.

Students may not be familiar with multicasting. A brief explanation may be required at this point. The following link provides information on Cisco IP multicast implementation.

http://www.cisco.com/warp/public/732/Tech/multicast

4.1.2 Information obtained with CDP

CDP is used to collect information about directly-connected devices. The types of information it collects are referred to as Type Length Values (TLVs). This TI includes a table that defines each TLV. Certain types of information are only included as a part of CDPv2. This information is noted in the table.

TLV Definition

Device-ID TLV Identifies the device name in the form of a

character string

Address TLV Contains a list of network address of both

receiving and transmitting devices

Port-ID TLV Identifies the port on which the CDP packet is

sent

Capabilities TLV Describes the functional capabilities of a device

in the form of a device type such as a switch

Version TLV Contains information about the software release

version on which the device is running

Platform TLV Describes the hardware platform name of the

device

IP Network Prefix TLV CDPv2 Contains a list of network prefixes to which the

sending device can forward IP packets. This information is in the form of the interface

protocol and port number such as Eth 0/1 VTP Management Domain TLV CDPv2

Native VLAN TLV CDPv2 Indicates the assumed VLAN for untagged

Full or Half Duplex TLV Indicates the status duplex configuration of a

Advertises the configured VTP management

domain name string of a network and is used by

network operators to verify VTP domain

configuration in adjacent network nodes

packets on each interface and is implemented

only for interfaces the support the IEEE 802.1Q

protocol

CDP broadcast interface and is used by network

administrators to diagnose connectivity

problems between adjacent network devices

The show cdp neighbors command displays CDP information collected by a device about its neighbors. It can be issued at a console connected to a Cisco network device.

Demonstrate the show cdp neighbors command and the show cdp neighbors detail command. Note that much of the information outlined in the table can only be seen if the detail option is utilized. This command variation is seen in subsequent RIOs. Some information is only displayed with CDPv2, which is implemented with IOS version 12.0(3)T.

Demonstrate how the show cdp neighbors command and its variations can be consoled into a router that is connected to another router or a switch to show students the output.

The show cdp neighbors command allows students to perform the associated Flash eLab.

4.1.3 Implementation, monitoring, and maintenance of CDP

CDP implemented by default on all interfaces that support it. The following table lists variations of the CDP command and their functions. These commands should be used in privileged EXEC mode. The table is located in this section of the curriculum.

Although not noted in the curriculum, many of these commands can be executed in user mode. Some of the configuration commands are done in global configuration mode and some require interface configuration mode.

Discuss the cdp enable and cdp run commands. The cdp enable command is an interface configuration command that enables CDP on a particular interface. The cdp run command is a global configuration command that enables CDP on a Cisco device. Students should also be comfortable with the no form of these commands. Relevant TIs from CCNA 2 v2.1.4 are 4.3.3 and 4.3.4.

Demonstrate command usage after the class reviews the table.

Command Purpose

cdp enable cdp advertise-v2 clear cdp counters show cdp

show cdp entry entry-name [protocol | version]

show cdp interface [type number]

show cdp neighbors [type number] [detail]

Enables CDP on an interface Enables CDP Version-2 on an interface Resets the traffic counters to zero Displays the interval between transmissions of

CDP advertisements, the number of seconds the CDP advertisement is valid for a given port, and the version of the advertisement

Displays information about a specific neighbor, which can be limited to protocol or version information

Displays information about interfaces on which CDP is enabled

Displays the type of device that has been discovered, the name of the device, the number and type of the local interface or port, the number of seconds the CDP advertisement is valid for the port, the device type, the device product number, and the port ID Displays information on the native VAN ID, the duplex mode, and the VTP domain name associated with neighbor devices when the detail keyword is used

4.1.4 Creating a network map of the environment

CDP uses advertisements to collect information about its neighbors. Its limitation is that it only collects information from directly-connected devices. The telnet command can be used in conjunction with cdp commands to create a network map. To do this, a network administrator can console into one router and use the telnet command to move from router to router.

If students have limited or no experience with the use of Telnet to move from device to device, this concept and skill should be reviewed. If students do not understand this capability, it will be difficult to understand the procedure described in this RIO. Demonstrate this capability if necessary. Refer to the figure to show students how telnet is used to map a network. Allow students to practice use of this command. Instruct students to map their router setup or a setup performed by another group.

4.1.5 Disabling CDP

Although CDP is enabled by default on all Cisco devices there may be situations in which CDP must be disabled. Three examples are included in the TI:

• If the bandwidth of a particular connection is inadequate, CDP can be disabled to conserve bandwidth.

• Since CDP is a Cisco proprietary device, if there is only one Cisco device on a network segment then there is no device with which to share information.

• If a particular device is connected to some other network such as an ISP, CDP can be disabled for security reasons. This will prevent the device from advertising information about itself to outside devices.

CDP can be disabled at two levels:

• The no cdp run command can be used in global configuration mode to disable CDP for the entire device. This should be used when only one Cisco device is present and CDP would serve no purpose on the network segment.

• CDP can be disabled for a specific interface. The network administrator must be in interface mode to perform this task. The command is no cdp enable or no cdp advertise-v2, based on the version of CDP that is used.

To determine if a particular interface has CDP enabled, the show cdp interface command can be used in user or privileged mode. The figures show the use of these commands.

Make sure students realize that CDP is enabled on all interfaces by default. Demonstrate how to disable CDP at the interface level and globally. Allow students to perform these commands on their own lab setup but ensure that students enable CDP when they are finished.

4.1.6 Troubleshooting CDP

CDP does not require any configuration. However there may be times when some of the following commands may be helpful in the troubleshooting process. A common problem may be devices with different versions of CDP. The show cdp neighbor command will show whether or not a device exists in the CDP neighbor cache and indicate if a device is utilizing version 2 of CDP.

Command Purpose

clear cdp table

Deletes information about neighbors from the CDP table

clear cdp counters show cdp traffic

show debugging

debug cdp adjacency debug cdp events debug cdp ip debug cdp packets cdp timers

cdp holdtime

show cdp

Review the following key points:

• CDP is Cisco proprietary.

Reset traffic counters to zero Displays CD counters such as the number of

packets sent and received and checksum errors Displays information about the types of debugging

that are enabled for the router Displays CDP neighbor information Displays CDP events Displays CDP IP information Displays CDP packet-related information Specifies how often the Cisco IOS software sends

CDP updates Specifies the hold time to be sent in the

CDP update packet Displays global CDP information such as timer and

hold-time information

• CDP runs on any SNAP-enabled media.

• CDP functions at Layer 2 and functions independent of the upper layers.

• CDP is used by all Cisco network devices such as routers, switches, and bridges.

• CDP utilizes periodic advertisements to obtain or update information about

directly-connected devices

Have students perform the CDP neighbor lab.

Web Links

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/fun_r/frprt3/frd3001b .htm

4.2 Getting Information about Remote Devices

Essential Labs: 4.2.2, 4.2.3, 4.2.4, 4.2.5a, 4.2.5b, and 4.2.6 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can perform simple LAN troubleshooting.

Certification-Level Claim: Students can troubleshoot a device that is part of a working network.

Hands-on skills: none

4.2.1 Telnet

Telnet provides network administrators with remote connection capability. It is a part of the TCP/IP protocol suite that operates at the application layer of the OSI model and the application layer of the TCP/IP model. The Telnet service in Cisco devices operates as a virtual terminal utility. Administrators can use Telnet to issue IOS commands when they are not directly connected to the device. Telnet consumes a vty session on the router when it is used. Remind students that vty lines 0 through 4 can be configured in a router configuration. Since Telnet is a vty connection, a router will support simultaneous Telnet connections.

Telnet also provides a tool for troubleshooting. The establishment of a Telnet connection confirms the connectivity and functionality of the application layer. The ping command only confirms Layer 3 connectivity.

4.2.2 Establishing and verifying a Telnet connection

From the router console, Telnet can be used to connect to remote devices. The administrator must type in the name of a router or the IP address of an interface to establish a Telnet connection. The following commands can be used:

Router>131.108.100.152 Router>paris Router>connect paris

Router>telnet paris

The figure includes an explanation of Telnet. The example shows how to console into a directly connected router and then establish a Telnet connection with other network devices. Telnet may also be used to connect a PC to the router, or other network device, through a network connection instead of using a direct console cable for the connection.

Students may not understand that Telnet is widely implemented. It is not used only within a network device to connect to other network devices. For example, Telnet can be used from the command prompt in Microsoft Windows. It can be used to connect to other PCs, servers, or devices.

Demonstrate various telnet connection commands.

4.2.3 Disconnecting and suspending Telnet sessions

Network administrators may need to establish multiple Telnet sessions. The keystroke CtrlShift-6 and then the letter X can be used to suspend a current Telnet session. The suspend

feature can be used to establish an additional Telnet session to another device. The show sessions command displays a numbered list of current Telnet sessions like the following

example.

Conn Host Address Byte Idle Conn Name

1 lab-a 192.168.10.1 0 0 lab-a

* 2 lab-e 192.168.10.1 0 0 lab-e

A connection can be resumed by selecting the corresponding number. The disconnect command will terminate a specific Telnet session. The procedure for disconnecting a Telnet session is as follows:

• Enter the disconnect command.

• Follow the command with the name or IP address of the router.

• Example: Denver> disconnect paris

The procedure for suspending a Telnet session is as follows:

• Press Ctrl-Shift-6 and then the letter X.

• Enter the name of the router or IP address of the next connection.

Students often think that the Ctrl-Shift-6, then X sequence will terminate a Telnet session. They need to understand that this only suspends the session. They also need to know how to resume and terminate a session

4.2.4 Advanced Telnet operation

A user may have multiple Telnet sessions open at the same time. The number is limited by the session limit. The user can switch between these sessions with the Ctrl-Shift-6 and then X key sequence. To resume a Telnet session, the resume command with the session id may be used. The connection id of all open Telnet sessions can be viewed with the show sessions command.

Command Purpose

Ctrl-Shift-6 then X Escapes the current connection and

resume

The resume [session number] command can be used to resume a Telnet session. The process id of a session can also be entered to resume the session.

returns to the EXEC prompt Makes the connection

The show sessions command output is as follows:

Stanly_Lab#show sessions

Conn Host Address Byte Idle Conn Name

1 lab-b 192.168.10.1 4 5 lab-b

2 lab-d 192.168.10.1 0 0 lab-d

* 3 lab-e 192.168.10.1 0 0 lab-e

4.2.5 Alternative connectivity tests

Connectivity can be tested with several other commands such as ping, traceroute, and show ip route. The ping command uses ICMP to send an echo request to a destination

and then awaits an echo reply from that destination. This is a good test for basic connectivity, reliability, and delay. This test can be performed from the user or privileged EXEC mode. A successful ping is indicated by exclamation points (!). A period (.) indicates a ping that has timed out.

The traceroute command is used to view the path that packets use to reach a particular destination. This is an excellent test to identify where packets are dropped in the network. An asterisk (*) indicates that the probe timed out. Traceroute will continue to reach the next router in a path until the process times out or it is interrupted by the Ctrl-Shift-6 escape sequence.

The purpose behind the traceroute command is to record the source of each ICMP "time exceeded" message to provide a trace of the path the packet took to reach the destination. The device executing the traceroute command sends out a sequence of User Datagram Protocol (UDP) datagrams, each with incrementing Time-To-Live (TTL) values, to an invalid port address (Default 33434) at the remote host.

First, three datagrams are sent, each with a TTL field value set to 1. The TTL value of 1 causes the datagram to "timeout" as soon as it hits the first router in the path. This router then responds with an ICMP "time exceeded" message indicating that the datagram has expired. Next, three more UDP messages are sent, each with the TTL value set to 2. This causes the second router in the path to the destination to return ICMP "time exceeded" messages.

This process continues until the packets reach the destination and until the system originating the traceroute has received ICMP "time exceeded" messages from every router in the path to the destination. Since these datagrams are trying to access an invalid port (Default 33434) at the destination host, the host responds with ICMP "port unreachable" messages indicating an unreachable port. This event signals the traceroute program to finish.

The show ip route command is used to identify the routes that are shown in the routing table. These are routes to directly connected networks, networks with static routes, or networks that have been learned through a routing protocol.

Due to many security configurations throughout the Internet, ping and trace may not always work to test connectivity through networking equipment outside of your control. Many firewalls and access-lists today do not allow ICMP traffic.

The procedure to use the ping command is as follows:

• ping IP address or name of destination

• Press Enter

The procedure to use the trace command is as follows:

• trace IP address or name of destination

• Press Enter

Demonstrate a successful ping.

LAB-B#ping lab-c

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echoes to 199.6.13.2, timeout is 2

seconds: !!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max =

32/35/36 ms

Demonstrate an unsuccessful ping.

LAB-D#ping lab-c

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echoes to 199.6.13.2, timeout is 2

seconds: .....

Success rate is 0 percent (0/5)

Demonstrate a successful trace.

LAB-A#trace lab-e

Type escape sequence to abort.

Tracing the route to LAB-E (210.93.105.2)

1 LAB-B (201.100.11.2) 32 msec 24 msec 24 msec

2 LAB-C (199.6.13.2) 32 msec 52 msec 40 msec

3 LAB-D (204.204.7.2) 64 msec 64 msec 64 msec

4 LAB-E (210.93.105.2) 60 msec * 64 msec

Demonstrate an unsuccessful trace.

LAB-A#trace lab-d

Type escape sequence to abort.

Tracing the route to LAB-D (204.204.7.2)

1 LAB-B (201.100.11.2) 36 msec 28 msec 24 msec

2 LAB-C (199.6.13.2) 36 msec 44 msec 40 msec

3 LAB-C (199.6.13.2) !H * !H

Show a routing table.

LAB-C#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

B – BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF

inter area, E1 - OSPF external type 1, E2 - OSPF external type

2, E – EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, *

- candidate default, U - per-user static route

Gateway of last resort is not set

C 204.204.7.0/24 is directly connected, Serial0

C 223.8.151.0/24 is directly connected, Ethernet0

R 201.100.11.0/24 [120/1] via 199.6.13.1, 00:00:06, Serial1

R 219.17.100.0/24 [120/1] via 199.6.13.1, 00:00:06, Serial1

R 192.5.5.0/24 [120/2] via 199.6.13.1, 00:00:06, Serial1

C 199.6.13.0/24 is directly connected, Serial1

R 205.7.5.0/24 [120/2] via 199.6.13.1, 00:00:06, Serial1

R 210.93.105.0/24 [120/1] via 204.204.7.2, 00:00:07, Serial0

4.2.6 Troubleshooting IP addressing issues

Addressing issues are the most common problems that occur on IP networks. Three commands can be used to perform troubleshooting:

• telnet – verifies the application layer software between the source and the destination. This is the most complete test mechanism available.

• ping – uses the ICMP protocol to verify the hardware connection and the IP address of the network layer. This is a very basic test mechanism.

• traceroute – is used to find failures in the path from the source to destination. Traceroute uses time-to-live values to generate messages from each router along the path.

Troubleshooting is one of the most important skills of a network associate. The majority of time in the workplace will be spent troubleshooting. Students should develop these skills at every opportunity. Help students learn the logical process, what to look for, and the tools to use. Always use the OSI model to teach troubleshooting from Layer 1 to Layer 7. For students to become proficient at troubleshooting, it must be a normal part of the labs. Each lab should include a troubleshooting session. This could be a discussion about problems that might be experienced in the lab or problems can be placed on the student network.

Module 4 Summary

Students must master CDP and network troubleshooting commands before they move on to Module 5

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 4 exam. Students should be familiar with the equipment that is in the room with them. If they need to see how it is connected, they can look at it. Another assessment option is to put several interconnected and configured routers in a taped box with a console cable and a power strip cord coming out of it. Mark the box with the name of a distant city. Then ask the students to draw a topology map of the internetwork of that city.

Students should understand the following main points:

• How to enable and disable CDP

• How to use the show cdp neighbors command

• How to determine which neighboring devices are connected to which local

interfaces

• How to use CDP to gather network address information about neighboring devices

• How to establish a Telnet connection

• How to verify a Telnet connection

• How to disconnect from a Telnet session

• How to suspend a Telnet session

• How to perform alternative connectivity tests

• How to troubleshoot remote terminal connections

Module 5: Managing Cisco IOS Software

Overview

When teaching Module 5, emphasize the importance of the router boot sequence. The router boot sequence verifies the proper operation of the router hardware, identifies the correct IOS and configuration file, and shows the location of each. This process must be understood to properly configure and operate all Cisco routers. Before students begin Module 5, they should be able to identify the purpose and operation of the IOS, use the show version command, and troubleshoot basic connectivity issues. In this section, students will learn about the Cisco IOS File System and how to use a variety of Cisco IOS software source options. Students will also learn how to use commands to load Cisco IOS software onto a router, maintain backup files, and upgrade Cisco IOS software.

Module Caution: Make sure students fully understand how to copy and paste configurations into a router. Make sure that they understand the importance of configuration management, especially backups.

Students who complete this module should be able to perform the following tasks:

• Identify the stages of the router boot sequence

• Describe how a Cisco device locates and loads the Cisco IOS

• Use the boot system command

• Identify the configuration register values

• Describe the files used by the Cisco IOS and their functions

• List the locations of the different file types on the router

• Describe the parts of the IOS name

• Use TFTP and copy-and-paste to save and restore configuration files

• Use TFTP to load an IOS image

• Use XModem to load an IOS image

• Use show commands to verify the file system

5.1 Router Boot Sequence and Verification

Essential Labs: 5.1.3 and 5.1.5 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can Identify the stages of the router boot-up sequence and

show how the configuration-register and boot system commands modify that sequence.

Certification-Level Claim: Students can describe the components of network devices. Hands-on skills: none

5.1.1 Stages of the router power-on boot sequence

The purpose of the router boot-up sequence is to verify the operation of hardware and load the correct IOS and configuration file. The router must follow a predefined set of steps while it boots up:

• When the router is first powered-on, it executes the power-on self test (POST). These diagnostics are located in ROM and verify the proper operation of the router hardware.

• If the router passes the POST, the bootstrap loader in ROM executes. The bootstrap basically indicates a starting point in memory that will load other instructions.

• Now the router is ready to load the operating system, which is Cisco IOS. The IOS can be found in flash, TFTP, or ROM. The boot field of the configuration register will indicate the location of the IOS image.

• After the operating system is loaded and operational, the configuration file from NVRAM is loaded and executed. If no configuration file exists in NVRAM, the router will prompt the user to use a question-driven setup menu.

Review the figure in this TI with the students. This is an excellent visual representation of the different aspects of the boot process. Each student should be able to reproduce this figure from memory. Remove the configuration from NVRAM to demonstrate the process used to check for a TFTP server and then enter the setup menu. Demonstrate the use of Ctrl-C to exit from the setup menu.

5.1.2 How a Cisco device locates and loads the Cisco IOS

The router can load the Cisco IOS from several different locations that can be specified by the operator. The boot system commands can be used to identify a fallback sequence of locations to look for the IOS.

It is important to realize that these boot system commands must be saved in NVRAM to be executed at the next start-up. If no boot system commands are saved in NVRAM, the router will use the default fallback process, flash, TFTP, and finally ROM.

Review the figure in this section to explain the process that is followed to load the IOS. Make sure students realize that network problems can affect the process when the IOS is loaded from a TFTP server. Explain that the IOS loaded from ROM is only a subset of the IOS loaded from flash.

The figure is not complete because ROM is not included.

5.1.3 Using the boot system command

The boot system command can be used to specify where and the sequence in which the router will look for the IOS. After the boot system command has been saved to the start-up configuration in NVRAM, it will be used in the next start up to locate the IOS. When the IOS is loaded from flash memory, it is located locally, which isolates the process from any network problems that might be associated with TFTP. The IOS may be loaded from a TFTP server if the flash memory has been corrupted. If the IOS is not loaded from flash or the TFTP server, a subset of the IOS can be loaded from ROM. Make sure students understand that the IOS

loaded from ROM is only a subset of the Cisco IOS software and might be an older version. Use the boot system command to specify a fallback sequence and save it to NVRAM.

Restart the router and allow the students to verify the boot system locations during the next start-up. Explain why it is important to save the boot system commands to NVRAM.

5.1.4 Configuration register

The configuration register is a 16-bit register that contains the boot field setting in the lowest four bits. This boot field can be changed with the config-register command and is verified with the show version command. The least significant bits indicate the location from which the router will be booted. Zero will cause the router to boot in ROM monitor mode, one will cause the router to boot from ROM, and two to F will cause the router to use the boot system command in NVRAM.

Configuration Register Setting Location from which the router will boot.

0x0 ROM monitor mode, manual boot 0x1 ROM, automatic 0x2 to 0xF NVRAM

More information can be found at the following website:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_command_reference_cha pter09186a00800ca506.html

5.1.5 Troubleshooting IOS boot failure

Students must be familiar with the boot sequence and the configuration register to be able to troubleshoot boot errors.

If the router does not boot properly, the show version command can be used to identify the configuration register setting. The boot field indicates where the router is configured to boot from and the config-register command is used to make any necessary changes.

If the router IOS does not boot properly, there are several things that could be wrong:

• Boot system statement in configuration file

• Incorrect configuration register value

• Corrupted flash image

• Hardware failure

Instruct students to use the show version command to check the configuration register value. When a router does not boot properly it is usually because the configuration register setting is incorrect. For students to understand the impact that the boot sequence and the configuration register has on routing, they must perform the hands-on labs. Make sure each student can complete and explain the labs. Discuss the results and purpose of the labs after they have been completed by all of the students.

Instruct students to verify the configuration register setting on a regular basis. Occasionally change the configuration register settings and allow them to troubleshoot the errors that occur.

Additional Resources

http://www.cisco.com/en/US/products/hw/routers/ps233/products_tech_note09186a00800a65 a5.shtml

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_summary_cha pter09186a00800801b1.html

5.2 Managing the Cisco File System

Essential Labs: 5.2.3, 5.2.5, 5.2.6a, and 5.2.6b Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can manage system image and device configuration files. Certification-Level Claim: Students can manage system image and device configuration

files. Hands-on skills: none

5.2.1 IOS file system overview

A router or switch requires software to operate. The following are two basic types of essential software:

• The operating system

• The config file

The operating system that is used in almost all Cisco devices is the Cisco IOS. The IOS is the software that allows the hardware to function as a router or a switch. The software a router or switch uses is referred to as the configuration, or config file. The configuration file contains the instructions that define how the device will route or switch.

The IOS is stored in Flash memory. The configuration file is stored in NVRAM. Discuss with the students the differences between these types of memory and help the student understand by opening a router and showing the inside of the router to the students. Discuss RAM, ROM, flash, and NVRAM. Students must understand the differences between them. One difference to discuss is that the IOS in flash or RAM is several megabytes and the configuration file in NVRAM is up to a few kilobytes.

Version 12 and newer releases of the IOS provide a single interface to all file systems. This is referred to as the Cisco IOS File System (IFS). The IFS can be used to perform all the file system management for a router. Explain that the IFS is based on UNIX file systems.

5.2.2 IOS naming convention

Many different versions of the IOS are available. The IOS supports many different hardware platforms and features. This is a continuous development process.

To identify the different versions, Cisco has a naming convention for the IOS files. The IOS naming convention uses different fields in the name such as hardware platform identification, feature set identification, and the numerical release.

The first part of the IOS filename identifies the hardware platform. The second part of the IOS filename identifies the various features that the file contains. The third part of the filename indicates the file format. It specifies if the IOS is stored in flash, if it is in compressed format, and if it can be released. The fourth part of the filename identifies the IOS release.

This is an important concept for students to understand. They should be able to look at an IOS filename and determine the hardware platform, features, file format, and the release. Students should also understand that these naming conventions vary for different releases. This occurs as the feature sets are rebundled and renamed.

Show students some of the tools for IOS planning that are available on the Cisco website. Most of these are only available to users who have obtained user ids through SmartNet.

http://www.cisco.com/warp/customer/620/1.html http://www.cisco.com/en/US/customer/products/sw/iosswrel/ios_abcs_ios_networking_the_ent

erprise0900aecd800a4e14.html

5.2.3 Managing configuration files using TFTP

The active configuration uses RAM and the default location for the startup configuration is NVRAM. Students must understand the differences between RAM, ROM, NVRAM, and flash. If the configuration is lost, there should be backup copies available. The backup configuration can be stored on a TFTP server. The copy running-config tftp command can be used to do this.

The steps to copy to a TFTP server are as follows:

• Enter copy running-config tftp

• Enter the IP address of the TFTP server at the prompt

• Enter the name to assign to the configuration file

• Answer yes each time to confirm the choices

The steps to copy from a TFTP server to restore the configuration file are as follows:

• Enter copy tftp running-config

• Select a host or network configuration file at the prompt

• Enter the IP address of the TFTP server where the config file is located

• Enter the name of the config file or accept the default name

• Confirm the configuration filename and the server address

Make sure students realize that there are other ways to back up a configuration file. Other methods will be discussed in later sections. It is important for students to understand this process and all the procedures that are explained. It is most important for students to understand that backups are an important part of network management.

5.2.4 Managing configuration files using copy and paste

Another way to create a backup copy of the configuration is to capture the output of the show running-config command. The output can be copied, pasted into a text file, and saved to

create an alternate backup copy. However, the file will need to be edited before it can be used to restore configuration to a router.

To capture the configuration in HyperTerminal, students should perform the following tasks:

• Select Transfer > Capture Text

• Specify the name for the text file

• Select Start

• Use the show running-config command to display the configuration

• Press the Spacebar when each -More- prompt appears

After the configuration has been displayed, students should select Transfer > Capture Text > Stop to stop the capture.

After the capture is completed, the configuration file needs to be edited to remove text that is not required to configure a router. Then it can be pasted back into the router if needed.

The configuration file can be edited from a text editor such as Notepad. The following steps are used to edit the file:

• Select File > Open

• Find the captured file and select it

• Click Open

The lines that need to be deleted contain the following:

• show running-config

• Building Configuration…

• Current Configuration

• -More-

• Any lines that appear after the word End

• At the end of each of the interface sections, students should add no shutdown.

• To save the clean version, select File > Save.

Before the configuration is restored, any remaining configuration should be removed from the router by issuing the command erase startup-configuration. Use the reload command to restart the router.

HyperTerminal can be used to restore the configuration:

• Enter global configuration mode.

• Select Transfer > Send > Text File in HyperTerminal.

• Select the name of the file.

• Read the lines of the file as they are entered into the router.

• Observe for any errors.

• Press Ctrl-Z to exit global configuration mode after the configuration file is entered.

• Use the copy running-config startup-config command to restore the

startup configuration file.

Students must understand each of the procedures. A backup configuration file is necessary for any network administrator. Explain that minimal down time is required in any network.

Discuss the difference between running configuration and startup-configuration. This concept is very important. Also stress the benefits of comments in the configuration. These comments can explain the function of the various commands. Make sure that the students know that these comment lines begin with an exclamation point (!) and that these lines are not stored in the router.

Some features of HyperTerminal do not work well with the version of HyperTerminal that comes with Windows XP. A free, educational upgrade to HyperTerminal 6.3 can be downloaded from the following website.

http://www.hillgrave.com/htpe/index.html

5.2.5 Managing IOS images using TFTP

A router may need to have an IOS upgrade or restored. A router should be backed up upon arrival. The IOS image can be stored in a central server with other IOS images to restore or upgrade the IOS into the router and switch. The server should use a TFTP service. The IOS upgrade can be initiated from the privileged EXEC mode with the command copy tftp

flash. The router will prompt the user to enter the IP address of the TFTP server and then request the filename of the IOS image. If there is not sufficient flash available, the router may prompt the user to erase flash. Flash will be erased before the new image is downloaded.

Students must realize that it is important to maintain current versions of the IOS to eliminate security problems and performance bugs. They also should know that the newer releases are larger and may require flash and RAM upgrades. To ensure a successful transfer, students can ping the TFTP server from the router to test reachability. Stress that when students enter a path name or the name of the IOS, the entry must be exact. If it is not exact, the procedure will not work. One technique is to cut and paste the name of the file from a Windows Explorer directory listing. Explain that this process takes time since the IOS is several megabytes and patience is required. Also point out that the letter e appears when flash is being erased and an exclamation point (!) indicates that a datagram has been successfully downloaded.

5.2.6 Managing IOS images using XModem

If the IOS image in flash has been erased or corrupted, the IOS may need to be restored from ROM monitor mode (ROMmon). First, the flash should be examined with the dir flash: command. If an image appears to be valid, an attempt should be made to boot from that image. This is done with the boot flash: command. If the router boots properly, then the students should determine why the router booted from the ROMmon prompt instead of flash. The show version command can be used to check the configuration register. Students can use the show startup-config command to see if there is a boot system command that instructs the router to use the IOS to monitor ROM.

If the router will not boot properly, a new IOS image will need to be downloaded. The IOS file can be recovered with one of the following methods:

• Use xmodem to restore the image through the console.

• Use TFTP from the ROMmon mode to download the image.

To restore the image through the console, the local PC needs to have a copy of the IOS file to restore and a terminal emulation program.

The default console speed of 9600 bps can be used or it can be changed to 115200 bps. This will speed up the download. The console speed can be changed with the confreg command.

To restore the IOS image from the PC, students should use the xmodem command. The format of the command is xmodem –c image_file_name. The -c instructs the Xmodem process to use CRC to check for errors during the download. The router then sends a warning message that the bootflash will be erased. Now the Xmodem transfer needs to be started from

the terminal emulator. Instruct students to select Transfer > Send and then specify the image name and location in the Send File popup. Select the xmodem protocol and start the transfer. After the download is complete, the console speed must be changed back to 9600 bps and the configuration register should be changed back to 0x2102. This is done with the confreg 0x2102 command.

5.2.7 Environment variables

The IOS can also be restored from a TFTP session. The fastest way to restore an IOS image from the router is to use TFTP from ROMmon to download the image. This is done with the tftpdnld command. The environmental variables provide a minimal configuration. To set a ROMmon environment variable, the name is typed, followed by an equal sign (=) and the value for the variable. All variable names are case sensitive. The minimum variables required to use the tftpdnld command are as follows:

• The IP address of the LAN

• The subnet mask

• The default gateway

• The IP address of the TFTP

• The IOS filename on the server

Discuss these procedures with the students and make sure they understand each concept. Also stress the fact that the fastest way to restore an IOS image to the router is to use TFTP from ROMmon to download the image.

http://www.cisco.com/en/US/customer/products/hw/routers/ps259/products_tech_note09186a0 08015bf9e.shtml

5.2.8 File system verification

There are several commands used to verify the router file system. One is the show version command. This command is used to check the current image and available flash. It also verifies the source of the IOS image and the configuration register boot field setting. The show flash command is also used to verify the flash system. This command identifies the amount of flash that is available. It also confirms that there is ample space to store a new IOS image. Configuration files may contain boot system commands. These identify the source of the desired boot IOS image. Multiple boot system commands are used to create a fallback sequence to discover and load an IOS. Boot system commands are processed in the order of their appearance in the configuration file.

Discuss the following alternatives with the students:

• NVRAM

• TFTP server

• ROM

Make sure the boot commands are reviewed. Stress the importance of familiarity with the bootup procedures.

Module 5 Summary

Students must be able to manage configuration files and verify the file system with show commands before they begin Module 6.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 5 exam.

Students should understand the following main points:

• Identify stages of the router boot sequence

• Identify how the Cisco device locates and loads the Cisco IOS

• Identify the configuration register settings

• Identify the files used by the Cisco IOS and their functions

• Identify the locations on the router of the different file types

• Identify the parts of the IOS name

• Manage configuration files using TFTP

• Manage configuration files using copy-and-paste

• Manage IOS images with TFTP

• Manage IOS images with Xmodem

• Verify the file system using show commands

Module 6: Routing and Routing Protocols

Overview

When teaching Module 6, remind students that routing refers to the directions that are given to move packets from one network to another. These directions, which are also known as routes, can be dynamically given to the router by another router, or they can be statically assigned to the router by an administrator. Make sure students understand static routing.

Module 6 Caution This information contains fundamental terminology that instructors may need to get the

students interested in learning about. Make sure students understand this material so that static and dynamic routing can be compared in future lessons.

Students who complete this module should be able to perform the following tasks:

• Explain the significance of static routing

• Configure static and default routes

• Verify and troubleshoot static and default routes

• Identify the classes of routing protocols

• Identify distance-vector routing protocols

• Identify link-state routing protocols

• Describe the basic characteristics of common routing protocols

• Identify interior gateway protocols

• Identify exterior gateway protocols

• Enable Routing Information Protocol (RIP) on a router

6.1 Introduction to Static Routing

Essential Labs: 6.1.6 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can identify, configure, and verify the use of static and default

routes.

Certification-Level Claim: Students can evaluate the characteristics of routing protocols. Hands-on skills: none

6.1.1 Introduction to routing

Routing is the process that a router uses to forward packets toward the destination network. The routing process is based on the destination IP address of a packet. When routers use dynamic routing, the routing information is learned from other routers. When static routing is used, a network administrator must configure information about remote networks manually. Any network topology changes require the network administrator to add and delete static routes to account for the changes.

Ask students the following questions:

• What is the difference between static and dynamic routing?

• When should a static route be used instead of a dynamic routing protocol?

6.1.2 Static route operation

Static route operations can be divided into three parts:

• Network administrator configures the route

• Router installs the route in the routing table

• Packets are routed through the static route

Since a static route is manually configured, the administrator must configure the static route on the router with the ip route command. The administrator can accomplish this objective in one of two ways. The administrator can specify the outgoing interface or the next-hop IP address of the adjacent router.

From Rt1 either of the following commands will work.

Rt1(config)#ip route 192.168.2.0 255.255.255.0 192.168.1.2

This command should be interpreted as “To reach the network 192.168.2.0 that has a subnet mask of 255.255.255.0, the next hop in the path is 192.168.1.2”.

Rt1(config)#ip route 192.168.2.0 255.255.255.0 s0

This should be interpreted as “To reach the network 192.168.2.0 that has a subnet mask of

255.255.255.0, send the packet out interface serial 0/0”. The administrative distance indicates the trustworthiness of the source of the route. The router

assigns an administrative distance of one to static routes by default. The router assumes that if an administrator takes the time to figure out what route the packet should take then this routing information must be very reliable. Only directly-connected routes have a default administrative distance that is trusted more. The default administrative distance for directly-connected devices is zero.

Administrative distance should not be confused with the metric of the route. The metric of the route indicates the quality of a route. When a router decides which route to a particular destination to put in the routing table, it compares the administrative distances of all the routes available to that destination. The router then examines the routes with the lowest administrative distances and chooses the one with the lowest metric.

If the interface that a packet is to be sent to on the next hop is not up, the route will not be installed in the routing table.

Here is an example of how a default administrative distance of 0 can be changed to an administrative distance of 255:

Rt1(config)#ip route 192.168.2.0 255.255.255.0 192.168.1.2 255

6.1.3 Configuring static routes

Use the following steps to configure static routes:

1. Determine all desired destination networks, their subnet masks, and their gateways. A gateway can be either a local interface or a next hop address that leads to the desired destination.

2. Enter global configuration mode.

3. Type the ip route command with the address and subnet mask of the destination followed by their corresponding gateway from Step 1. An administrative distance is optional.

4. Repeat Step 3 for as many destination networks as were defined in Step 1.

5. Exit global configuration mode.

6. Save the active configuration to NVRAM by using the copy running-config startup-config command.

Here is an example of a route from Rt1 to network 192.168.2.0.

Rt1#config terminal Enter configuration commands, one per line. End with CNTL/Z. Rt1(config)#ip route 192.168.2.0 255.255.255.0 192.168.1.2 Rt1(config)#exit Rt1# Rt1#copy running-config startup-config Destination filename [startup-config]? Building configuration... Rt1#

All routers must be configured. If Rt2 does not have a route back to network 192.168.0.0, a ping from network 192.168.0.0 will make it to network 192.168.2.0, but will not know how to get back. A relevant TI from CCNA 2 v2.1.4 is 12.1.4.

6.1.4 Configuring default route forwarding

Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. A default route is actually a special static route that uses the following format:

ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

Use the following steps to configure default routes:

1. Enter global configuration mode.

2. Type the ip route command with 0.0.0.0 for the destination network address and

0.0.0.0 for the subnet mask. The gateway for the default route can be either the local router interface that connects to the outside networks or the IP address of the next-hop router. In most cases, the IP address of the next hop router should be specified.

3. Exit global configuration mode.

4. Save the active configuration to NVRAM with the copy running-config startup-config command.

Here is an example for Rt1.

Rt1#config terminal Enter configuration commands, one per line. End with CNTL/Z. Rt1(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.2 Rt1(config)#exit Rt1# Rt1#copy running-config startup-config Destination filename [startup-config]? Building configuration... Rt1#

Remind students of different types of router modes.

6.1.5 Verifying static route configuration

After static routes are configured it is important to verify that they are present in the routing table and that routing occurs as expected. The show running-config command is used to view the active configuration in NVRAM to verify that the static route was entered correctly.

interface Serial0/0 ip address 192.168.1.1 255.255.255.0 no ip directed-broadcast no fair-queue clockrate 56000 ! interface FastEthernet0/0 ip address 192.168.0.1 255.255.255.0 no ip directed-broadcast no keepalive ! ip classless ip route 192.168.2.0 255.255.255.0 Serial0

The show ip route command is used to make sure that the static route is present in the routing table.

The output of show ip route is as follows.

Show ip route output Rt1#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B – BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2, E1 - OSPF external type 1, E2 - OSPF external type 2, E – EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area, * - candidate default, U - peruser static route, o – ODR, P - periodic downloaded static route

Gateway of last resort is not set

C 192.168.0.0/24 is directly connected, FastEthernet0/0 C 192.168.1.0/24 is directly connected, Serial0/0 S 192.168.2.0/24 is directly connected, Serial0/0 Rt1#

6.1.6 Troubleshooting static route configuration

The show interfaces command can be used to check the state and configuration of the interface that will be used for the route gateway. The ping command is used to determine if end-to-end connectivity exists. If an echo reply is not received after a ping, the traceroute command will be used to determine which router in the route path is dropping the packets.

Here are the outputs of the show interface, ping, and traceroute commands.

Rt1#show interfaces s0 Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Internet address is 192.168.1.1/24 MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation HDLC, loopback not set Keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters 00:35:48 Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 194 packets input, 12076 bytes, 0 no buffer Received 194 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 194 packets output, 12076 bytes, 0 underruns 0 output errors, 0 collisions, 5 interface resets 0 output buffer failures, 0 output buffers swapped out 1 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up Rt1# Rt1#ping 192.168.2.1

Use the escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.2.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/32/36 ms Rt1# Traceroute command from Rt1. Rt1#traceroute 192.168.2.1 Type escape sequence to abort. Tracing the route to 192.168.2.1 1 192.168.1.2 16 msec 16 msec * Rt1#

6.2 Dynamic Routing Overview

Essential Labs: None Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can evaluate the characteristics of routing protocols. Certification-Level Claim: Students can evaluate the characteristics of routing protocols. Hands-on skills: none

6.2.1 Introduction to routing protocols

A routing protocol is a type of communication that is used between routers. A routing protocol allows one router to share information with other routers such as known networks and how close they are to the router. The information a router gets from another router through the routing protocol is used to build and maintain a routing table.

A routed protocol is used to direct user traffic. A routed protocol is a network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme. The Internet Protocol (IP) is an example of a routed protocol. Students should know the difference between a routed and routing protocol at the end of this TI. Identify the location of each protocol in the OSI model. Ask students the following questions:

• TCP is at which layer?

• IP is at which layer?

• Is the protocol connection-oriented or connectionless?

• RIP, IGRP, EIGRP, and OSPF are at which layer and what is the administrative

distance of each?

6.2.2 Autonomous systems

An autonomous system is a collection of networks under a common administration that share a common routing strategy. Some routing protocols use an autonomous system to communicate routing information. The routers are configured with the routing protocol and the autonomous system number. Each router can only communicate with other routers within the same autonomous system.

To demonstrate this concept, divide the classroom into groups and tell the students they can only talk to the people in their group. This is similar to a protocol that uses autonomous system numbers. It is possible for routers with different autonomous system numbers and different protocols to communicate if redistribution is used. Redistribution will not be covered in this section.

At this point, students do not have to understand the details of an autonomous system. They just need to understand the basic concepts of an autonomous system. Students do not have enough experience to understand policy-based routing.

6.2.3 Purpose of a routing protocol and autonomous systems

The goal of a routing protocol is to fill the routing table with known networks or destinations and the best route to reach these destinations. Although routers can forward packets without a routing protocol configured, using a protocol allows for dynamic updates. The router can be configured with static routes. When static routes are used, the administrator must configure a route for each network. Instruct the students to think of all the networks on the Internet and the different paths to each network. Then instruct the students to think about how fast the Internet changes. A routing protocol will dynamically learn routes to all networks even when the paths change.

The router knowledge needs to reflect an accurate, consistent view of the topology. This view is called convergence. When all routers in an internetwork use the same knowledge, the internetwork is said to have converged. This means all the routers have agreed on the reachable networks.

The purpose of autonomous systems is to segregate the entire network into administrations. If all the routers needed to communicate with all other routers on the Internet, each router would have a tremendous number of routes and would use large amounts of bandwidth to share the routes with the other routers. This is referred to as overhead for the routers. More overhead will increase hardware requirements. When a network is divided into autonomous systems, only the routers inside the local AS receive details about the routing information. Routers in other autonomous systems only need a summary of the routing information. This reduces the number of routes and the amount of routing information that has to be shared, which reduces router overhead. It also improves network stability since routing updates that are caused by topology changes do not have to be shared outside of the local AS. Some routing protocols can be used divide an AS into smaller units to provide the same benefits.

6.2.4 Identifying the classes of routing protocols

Most routing algorithms can be classified as one of three basic algorithms:

• Distance vector

• Link state

• Balanced hybrid

Routers will determine which route to take to a given network based on the type of algorithm that is used. Each of the three types has advantages and disadvantages.

6.2.5 Distance vector routing protocol features

Distance vector routing algorithms are used to send periodic copies of a routing table. Each router receives a routing table from its directly-connected neighboring routers. RIP sends its entire table every 30 seconds and IGRP sends its entire table every 90 seconds. The algorithm eventually accumulates network distances so that it can maintain a database of

network topology information. This is measured in hop counts, or the number of routers in the path to a destination network.

Distance vector algorithms do not allow a router to know the exact topology of an internetwork. The router only uses hop count to determine the best path. Distance vector algorithms require each router to send its entire routing table to each of its neighbors. This creates network traffic and there is a limit to the number of hops a distance vector routing protocol will use. The RIP maximum hop count is 15 and IGRP is 255. Explain that distance vector routing protocols use the view of neighboring routers to develop their view of the internetwork. The router will use copies of neighboring routing tables to build its routing table.

6.2.6 Link-state routing protocol features

The second basic algorithm used for routing is the link-state algorithm. Link-state algorithms are also known as Dijkstras algorithms.

Link-state routing uses the following:

• A topological database

• The SPF algorithm and the resulting SPF tree

• A routing table of paths and ports to each network

• A link-state advertisement (LSA), which is a small packet sent between routers

that contains link information

Link-state routing requires more memory. Routers send updates when there is a change in the table. There is less network traffic because the routers are not sending updates every 30 or 90 seconds. The routers in an area elect a Designated Router (DR) and a Backup Designated Router (BDR). When a change is made in the network, the router that notices the change sends an update to the DR. When an update occurs, only the change is sent instead of the entire routing table. The DR then sends the network change to all routers in the area with a multicast.

An important concept to mention is that routers that use a link-state routing protocol develop a common view of the internetwork. A link-state protocol collects links from neighboring routers to create a routing table. Students also need to understand that the updates from the routers contain information about the links. These links can be locally connected or received from other routers. Students also need to know that the updates are partial updates.

6.3 Routing Protocols Overview

Essential Labs: None Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can evaluate the characteristics of routing protocols.

Certification-Level Claim: Students can evaluate the characteristics of routing protocols. Hands-on skills: none

6.3.1 Path determination

Path determination occurs at the network layer, or Layer 3, for traffic that goes through a network cloud. The path determination function enables a router to evaluate the available paths to a destination and to establish the preferred way to handle a packet. This information can be configured by a network administrator or collected through the dynamic processes that operate in the network. Routing protocols help prevent routing loops and use fewer resources. An administrator can configure static routes for all reachable networks. Routers perform two primary functions:

• Path selection

• Switching

During path selection, the routing table is examined to determine the next hop destination of a packet and which interface to use to reach that next hop destination. Switching occurs when a packet is moved to the interface and a frame is created to send the information.

6.3.2 Routing configuration

Global and interface parameters must be set when an IP routing protocol is selected. Global tasks include the selection of a routing protocol, either RIP or IGRP, and IP network numbers must be indicated. It is important to check the interface IP address and subnet configuration. A common problem is to assign the wrong IP address or subnet mask. The network command is required because it enables the routing process to determine which interfaces will send and receive routing updates. A network statement must be entered for all connected networks. Two common problems are failure to enable the routing protocol or failure to enter all the connected networks.

6.3.3 Routing protocols

Examples of IP routing protocols include the following:

• RIP – a distance-vector interior routing protocol

• IGRP – a Cisco distance-vector interior routing protocol

• OSPF – a link-state interior routing protocol

• EIGRP – a balanced hybrid distance-vector interior routing protocol

• BGP – an exterior routing protocol

Make sure students understand that each routing protocol has advantages and disadvantages. The protocols have different characteristics and were designed for different purposes. In some instances administrators will want to use RIP and other times they will use BGP.

6.3.4 IGP versus EGP

Interior routing protocols are designed to be used in a network that is under the control of a single organization. The protocols used in CCNA 2 will be IGPs. The protocols RIP, IGRP, EIGRP, and OSPF are all IGPs. Exterior routing protocols are designed for use between two different autonomous systems. An example of an EGP protocol is Border Gateway Protocol (BGP). BGP is the routing protocol used on the Internet. Interior routing protocols are designed to be used within an autonomous system. BGP is the routing protocol used on the Internet. Interior routing protocols are designed to be used within an AS.

Module 6 Summary

Before students begin Module 7, they must be able to configure static routes and use the show ip route, ping, and traceroute commands to perform basic network testing.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 6 exam. Formative evaluations of students as they work on the routers may be valuable in this module.

Students should understand the following main points:

• A router will not forward a packet without a route to a destination network.

• Network administrators must manually configure static routes.

• Default routes are special static routes that provide routers with gateways of last

resort.

• Static and default routes are configured with the ip route command.

• Static and default route configuration can be verified with the show ip route,

ping, and traceroute commands.

• How to verify and troubleshoot static and default routes

• Routing protocols

• Autonomous systems

• Purpose of routing protocols and autonomous systems

• The classes of routing protocols

• Distance vector routing protocol features and examples

• Link-state protocol features and examples

• Route determination

• Routing configuration

• RIP, IGRP, OSPF, EIGRP, and BGP routing protocols

• Autonomous systems and IGP versus EGP

• Distance vector routing

• Link-state routing

Module 7: Distance Vector Routing Protocols

Overview

When teaching module 7, emphasize both skills development and conceptual understanding of the routing protocols RIP and IGRP. Students must master the basic routing skills and concepts from this module to be successful in CCNA 3.

Before students begin this section, they should be able to connect to Cisco routers and switches with serial or Ethernet cables, console and Telnet into a router, and configure TCP/IP on router interfaces

Module 7 Caution Many students do not have prior experience with routing protocols. Encourage the students to

spend plenty of time in the labs and to experiment with RIP. Since the labs are complex, students may require additional time, which may affect the availability of lab equipment. Provide guidance on how to follow an effective, well-documented, and patient troubleshooting strategy, since students may need to troubleshoot their labs. If the lab IOS does not support IGRP, instructors should use EIGRP and emphasize how it is similar to IGRP. EIGRP is covered in CCNA 3.

Students who complete this module should be able to perform the following tasks:

• Describe how routing loops can occur in distance vector routing

• Describe several methods used by distance vector routing protocols to ensure that

routing information is accurate

• Configure RIP

• Use the ip classless command

• Troubleshoot RIP

• Configure RIP for load balancing

• Configure static routes for RIP

• Verify RIP

• Configure IGRP

• Verify IGRP operation

• Troubleshoot IGRP

7.1. Distance Vector Routing

Essential Labs: None Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can identify, analyze, and show how to rectify inherent

problems associated with distance vector routing protocols. Certification-Level Claim: Students can troubleshoot and configure routing protocols based

on user requirements.

Hands-on skills: none

7.1.1 Distance vector routing updates

Distance vector routing protocols require routers to forward their entire routing table when passing along updates. Convergence is a step-by-step process with distance vector routing protocols. This means that routing table information is forwarded to neighbor routers, which continue to forward the information to their neighbors. This is contrasted with link-state routing protocols, which forward their routing tables out to all routers in their area. These routing tables include information about the total cost of a route and the logical address of the first router on the path to each network contained in the table.

Routers need to update the information in their routing tables to continuously make good path determination decisions. Periodically, changes in a network will affect the decisions made by a router. For example, a router may be taken off line for upgrades or repairs or an interface on a router may go down. If routers are not aware of the changes that have occurred in a network, they may switch packets to interfaces that are no longer connected to the best route.

Distance vector routing protocols typically send out updates at certain time intervals such as every 30 seconds for RIP. Sometimes distance vector routing protocols initiate updates when topology changes occur. For example, IGRP sends out flash updates sooner than its standard update interval of 90 seconds.

7.1.2 Distance vector routing loop issues

Routing loops can occur if slow convergence on a network causes inconsistent routing entries. If a network goes down, this information may not get propagated across the network quickly enough. As a result, a router may develop an incorrect view of the network and send out this incorrect information.

Use the following example in class:

• Just before the failure of Network 1, all routers have consistent knowledge and correct routing tables. The network is said to have converged. Assume for the remainder of this example that for Router C, the preferred path to Network 1 is by way of Router B and the distance from Router C to Network 1 is three.

• When Network 1 fails, Router E sends an update to Router A. Router A stops routing packets to Network 1, but Routers B, C, and D continue to route packets because they have not yet been informed of the failure. When Router A sends out its update, Routers B and D stop routing to Network 1. However, Router C has not received an update. Router C still tries to reach Network 1 through Router B.

• Now Router C sends a periodic update to Router D, which indicates a path to Network 1 through Router B. Router D changes its routing table to reflect this incorrect information and propagates the information to Router A. Router A propagates the information to Routers B and E and the process continues. Any packet that is destined for Network 1 will now loop from Router C to B to A to D and back again to C.

Problem: Routing Loops

Convergence is when all routers have the same information about the network. Convergence is a by-product of the routing updates that are sent out based on the routing protocol used on a router. If updated information does not reach all routers in a network quickly enough, then incorrect routing information may be sent out by routers that have not received the updates, which will replace the correct information in other routers.

In the example, Router C sends out an update to neighbor routers that incorrectly indicates that a route to Network 1 exists. This is a timing issue. Router C sends out updates before its neighbors have a chance to send out their newly updated information. Therefore, the accurate information is replaced by inaccurate information, which creates a routing loop.

A kinesthetic activity may be helpful to students to get a mental picture of how this process occurs. Instruct students to write their updates on paper and reenact the scenario from the figure and description.

7.1.3 Defining a maximum count

The previous section described a situation in which slow convergence created the impression that a fictitious path to a network existed, which leads to a routing loop. Routing loops have a packet that circles a network, uses up bandwidth, and never reaches its destination. Distance vector algorithms are designed to prevent these loops by defining a maximum hop count. This value is known as a routing metric. A metric is the criteria used by a router to determine the best path to a destination network. Metrics vary for different protocols. Some protocols such as RIP use only the metric of hop counts. Other routing protocols may use bandwidth, delay, and other factors. If the only metric used by a routing protocol is hop count then a router makes its path determination decisions based on the lowest number of routers that a packet will have to pass through to reach its destination.

The maximum hop count value defines how many routers a packet can pass through before the destination network is unreachable. Each time a packet passes through a router the distance number is increased. When the default or defined maximum is reached the network is considered unreachable and the looping ceases. A non-technical example is a timed test. If someone takes a timed test they have a predefined amount of time to complete it. When the maximum amount of time has been reached, the test ends even if some questions have not been answered.

7.1.4 Eliminating routing loops through split horizon

Another possible source for a routing loop occurs when incorrect information that has been sent back to a router contradicts the correct information that it sent. The following example explains how this problem occurs:

1. Router A passes an update to Router B and Router D that indicates that Network 1 is down. Router C transmits an update to Router B that indicates that Network 1 is available at a distance of four, by way of Router D. This does not violate split-horizon rules.

2. Router B incorrectly concludes that Router C still has a valid path to Network 1 at a less favorable metric. Router B sends an update to Router A to inform Router A of the new route to Network 1.

3. Router A now determines that it can send to Network 1 by way of Router B, Router B determines that it can send to Network 1 by way of Router C, and Router C determines that it can send to Network 1 by way of Router D. Any packet that is introduced into this environment will loop between routers.

4. Split-horizon attempts to avoid this situation. As shown in Figure [1], if a routing update about Network 1 arrives from Router A, Router B or Router D cannot send information about Network 1 back to Router A. Split-horizon reduces incorrect routing information and reduces routing overhead. [2]

Figure [1]: Routing Update

Figure [2]: Split Horizon

Split horizon is another mechanism to help prevent routing loops. Split horizon does not allow the originator of network information to receive updates about the network from another router. This prevents the originator of correct information from being influenced by the incorrect information of another router.

Use the figure in this section for reference. If Router 2 sends out an update to Router 1 about the status of Network A, it cannot receive a report back from Router 1 about Network A.

From the description in the curriculum, which is included above, if split horizon were in use in Step 2, Router A would have ignored information about Network 1 from Router B. More specifically, Router B would not have attempted to update Router A about that particular network in the first place because Router A originally informed Router B about the status of Network 1. Refer to Figure [1] Routing Update for a graphical representation of this process.

7.1.5 Route poisoning

Route poisoning is another process used by routers to prevent routing loops. Briefly review the fact that routing loops are typically the result of slow convergence. The loops are interrupted when maximum hop counts are defined so that packets that are caught in loops are eventually dropped. Route poisoning is when the distance or hop count of a route is changed to 16, or 1 higher than the maximum number allowed, which makes it unreachable from the perspective of the routers. This process of route poisoning results in an update about the poisoned route that is sent out to neighboring routers before the routing update time has been reached.

Router B

Reference the graphic in this section. When Router A determines that Network X is down, it poisons the route in its table. To do this, it sets the hop count to Network X to one more than the maximum. It then sends a poison update to Router B regardless of the time schedule for routing updates. This does not send the entire table. It only sends the route poisoning. This single change, which indicates that Network X is now unreachable, is quickly propagated through the network. This speeds convergence and reduces the likelihood that a loop will develop.

Router A

7.1.6 Avoiding routing loops with triggered updates

Routing table updates are automatically sent out at specific time intervals by distance vector routing protocols. As discussed earlier, slow convergence can create a scenario in which routers incorrectly think a route to a network is available, which results in a routing loop. Triggered updates such as route poisoning help prevent these routing loops by sending out updates when topology changes occur without waiting for the update time to be reached. This speeds up convergence in relationship to network topology changes.

Reference the graphic in this section. A triggered update would occur if Network X went down. Router C would detect the change, update its routing table, and then send out an update to Router B even though its update timer is set at 18. IP RIP would send out table updates at 30 seconds and IGRP would send them out at 90 seconds. This triggered update would poison the route until the holddown timer, which is discussed in the next section, has expired.

Make sure students understand that a triggered update is generated by the router that detects a topology change and sends the update to its neighbors.

7.1.7 Preventing routing loops with holddown timers

Holddown timers are used to prevent update messages from reinstating inaccessible routes. When a router receives an update that indicates that a network is unreachable, it starts a holddown timer. While the hold-down timer is running, the router will not accept any updates about the inaccessible route unless the update comes from the originator of the triggered update or from a router reporting a better metric to the inaccessible network.

If a router receives routing update information from a router other than the originator of the triggered update that says it has a route to the inaccessible network with a lower metric than the original metric, the router ignores the update information while the holddown timer is still in effect.

Holddown timers are used to allow updates about bad routes to be propagated. Routers that have already received the information will not accept update information about the bad route from neighbor routers that may not know that it is inaccessible.

Students may need some additional help with distance vector routing protocols. Several of the topics will be discussed later in the RLO. It may be helpful to discuss related concepts such as holddown timers, route poisoning, and triggered updates in a combined lesson with the entire class. Group discussions about how these features fit together to help prevent routing loops may be helpful to students.

7.2 RIP

Essential Labs: 7.2.2, 7.2.6, 7.2.7, and 7.2.9 Optional Labs: None Core TIs: All Optional TIs: none Course-Level Claim: Students can configure, verify, analyze, and troubleshoot simple

distance vector routing protocols. Certification Level Claim: Students can troubleshoot and configure routing protocols based

on user requirements. Hands-on skills: none

7.2.1 RIP routing process

RIP is a distance-vector routing protocol that uses hop count as the metric for path selection. By default, the maximum hop count for RIP is 15 and routing updates are broadcast every 30 seconds. If RIP routes are received that would increase the metric to a number higher than 15 hops, the network is considered unreachable and the route is discarded. RIP also has other features that are used by distance vector routing protocols such as split horizon and holddown mechanisms to prevent incorrect routing information from being propagated.

7.2.2 Configuring RIP

Basic RIP configuration consists of two steps:

1. Enable the routing protocol

2. Identify the directly connected networks, or the networks to advertise

The global configuration command router rip is used to enable RIP as the routing protocol. The network network address command allows the identification of directly-connected networks that will participate in the routing process. When the basic configuration of RIP is complete, regular updates are sent every 30 seconds and triggered updates are sent upon notification of metric changes.

The following is an example of RIP configuration:

 BHM(config)#router rip – selects RIP as the routing protocol  BHM(config-router)#network 1.0.0.0 – specifies a directly connect network  BMH(config-router)#network 2.0.0.0 – specifies a directly connect network

Notice that the network statements configured under the RIP protocol are classful addresses. Students commonly configure the network command by using the IP address of the subnet. The IOS will change this to the classful network address.

The router interfaces associated with the directly connected networks will participate in the routing process. These interfaces will send and receive routing updates.

RIP can be further customized through the use of some optional configuration parameters:

• Apply offsets to routing metrics

• Adjust timers

• Specify a RIP version

• Enable RIP authentication

• Run IGRP and RIP concurrently

• Disable the validation of source IP addresses

• Enable or disable split horizon

7.2.3 Using the ip classless command

The ip classless command allows packets that are bound for an unknown subnet to be routed out the same interface as other known subnets in the same range of addresses. IP classless only affects the operation of the forwarding processes in IOS. It does not affect the way the routing table is built.

When the no ip classless command is used, a packet bound for an unknown subnet will be dropped even if a route to a subnet in the same address range exists. The basic principle of classful routing is that if one part of a major network is known, but the subnet toward which the packet is destined within that major network is unknown, the packet is dropped. One aspect of this rule that may confuse students is that the router will only use the default route if the destination major network does not exist in the routing table at all.

7.2.4 Common RIP configuration issues

RIP is a distance-vector routing protocol and like all distance-vector protocols they are slow to converge and have to deal with routing loops and counting to infinity. To reduce the routing loops and counting to infinity, RIP uses the following mechanisms:

• Split horizon

• Poison reverse

• Holddown counters

• Triggered updates

RIP permits a maximum hop count of 15 and any destination greater than 15 hops away is tagged as unreachable. This maximum hop count prevents counts to infinity and endless network routing loops. The split horizon rule prevents information about a route from being sent out the same interface from which it was originally received. Split horizon is used to avoid the creation of routing loops due to multiple routers that advertise routes to each other about the same network. The no ip split-horizon command can be used to disable split horizon.

Hold-down timers are used to define the amount of time that a possible down route will be held and routes with higher metrics to the same network will not be accepted. The default holddown time is 180 seconds, which is 6 times the regular update period. When a route goes down, the hold-down timer is started. During this time period, a route with a higher metric than the original metric will not be accepted. If the original route comes back up or a route with a lower metric than the original metric is advertised, they will be accepted immediately. The hold-down timer will reduce routing loops but it may also slow convergence. The timers

basic 30 90 180 540 router configuration command can be used to adjust the basic timers. The holddown is the third number.

RIP updates are broadcast by default every 30 seconds. This can be increased to reduce network congestion or decreased to improve convergence with the timers basic 30 90 180 540 command. The update timer is the first number listed. In some instances, it may necessary to avoid the advertisement of routing updates out a specific interface. This can be accomplished with the passive-interface interface router configuration command. For RIP to function in a non-broadcast environment, neighbor relationships must be configured. This can be accomplished with the neighbor ip address router configuration

command. The RIP version can also be changed with the version [1 | 2] router configuration command. Other variations of this command may be placed on the interface to specify which version of packets to send and receive.

7.2.5 Verifying RIP configuration

The show ip protocol and the show ip route commands can be used to verify the configuration of RIP. The show ip protocol command displays information about all of the IP routing protocols that are used on the router. This command can be used to verify that RIP is configured, interfaces are correctly sending and receiving RIP updates, and that the router is advertising the correct networks. The basic timers, filters, and version can also be verified with the show ip protocol command. The show ip route command can be used to verify that RIP routes are received. These routes will be identified by an “R”, which indicates that they were learned through RIP.

7.2.6 Troubleshooting RIP update issues

Some common RIP configuration errors include incorrect network statements, discontiguous subnets, and split horizons. These RIP update issues can be identified with some basic show and debug commands. The debug ip rip command enables rip debugging and will display all of the rip updates as they are sent and received. The following is an example of the output of the debug ip rip command:

LAB-A#debug ip rip RIP protocol debugging is on LAB-A# RIP: ignored v1 update from bad source 223.8.151.1 on Ethernet0 RIP: sending v1 update to 255.255.255.255 via Ethernet0 (192.5.5.1) network 204.204.7.0, metric 3 network 223.8.151.0, metric 3 network 201.100.11.0, metric 1 network 219.17.100.0, metric 2 network 199.6.13.0, metric 2 network 205.7.5.0, metric 1 network 210.93.105.0, metric 4 RIP: sending v1 update to 255.255.255.255 via Ethernet1 (205.7.5.1) network 204.204.7.0, metric 3 network 223.8.151.0, metric 3 network 201.100.11.0, metric 1 network 219.17.100.0, metric 2 network 192.5.5.0, metric 1 network 199.6.13.0, metric 2 network 210.93.105.0, metric 4 RIP: sending v1 update to 255.255.255.255 via Serial0 (201.100.11.1) network 192.5.5.0, metric 1 network 205.7.5.0, metric 1 RIP: ignored v1 update from bad source 219.17.100.1 on Ethernet0 RIP: received v1 update from 201.100.11.2 on Serial0

204.204.7.0 in 2 hops

223.8.151.0 in 2 hops

219.17.100.0 in 1 hops

199.6.13.0 in 1 hops

210.93.105.0 in 3 hops

Other commands that can be used to troubleshoot RIP update issues include the following:

• show ip rip database

• show ip protocols

• show ip route

• debug ip rip

• show ip interface brief

7.2.7 Preventing routing updates through an interface

The passive interface command prevents routing updates from being sent out a particular interface. In the graphic, Router Z interface Fa0/0 is not allowed to send router updates to Router A. This may be implemented for a variety of reasons. One reason might be that the administrator of Router Z does not want information about the internal network to be sent out to other routers. If Router Z is a stub network, the administrator of Router A may prevent routing updates from being sent to Router Z since there is one way in and one way out. Students must understand that routes will still be learned through this interface. They also need to know that the network that this interface is connected to is advertised if a network statement is configured for that network.

7.2.8 Load Balancing with RIP

Load balancing is the process of routing packets over multiple equal-cost paths to increase throughput. RIP can load balance over as many as six equal-cost paths, although four is the default. Packets are sent “round robin” over the equal-cost paths, this means that the equalcost paths are used in turn. Since the metric for RIP is hop count, equal-cost paths indicate that a network can be reached through multiple paths that have the same hop count.

This does not consider the bandwidth of each link. So while load balancing may allow packets to travel multiple paths to reach a destination, huge bandwidth differences among equal-cost paths could actually slow throughput.

7.2.9 Load balancing across multiple paths

A router may have multiple paths to a given destination network. If these paths have different metrics the router will use the route with the best metric to forward packets. If multiple routes have the same metric associated with them, the router will use load balancing to spread out the traffic that is forwarded to a particular network. This helps reduce traffic on a given route to speed up communications. Load balancing is enabled by default on routers that use RIP and IGRP. With the exception of BGP, IP routing protocols route to four parallel routes by default. The administrator also has the option of load balancing on a per-packet or per-destination basis. A per-destination basis implies that all packets headed for a particular host on the network during a given communication session will take the same path.

Students should be comfortable with the term “round-robin” load balancing. This means that packets will be equally shared between the equal paths. This is done by alternating the packet output between the interfaces for each of the paths. The students should also understand that this does not equally balance the traffic between the paths. This is because the packets are of various sizes. So even though the same number of packets will be forwarded out of the interfaces, the amount of traffic will vary.

7.2.10 Integrating static routes with RIP

Static routes are user-defined routes that force packets to take a specific path. These are usually used when a dynamic route cannot be built, the overhead of dynamic routing is not desirable, or if another route for fault tolerance is desired. A static route can be configured on the router with the ip route command and removed with the no ip route command. These routes can then be redistributed or shared through the dynamic routing protocol with the redistribute static command.

7.3 IGRP

Essential Labs: 7.3.5 and 7.3.6 Optional Labs: 7.3.8 Core TIs: All Optional TIs: none Course-Level Claim: Students can configure, verify, analyze, and troubleshoot simple

distance vector routing protocols. Certification-Level Claim: Students can troubleshoot and configure routing protocols based

on user requirements. Hands-on skills: none

7.3.1 IGRP features

IGRP is a Cisco proprietary distance-vector interior gateway routing protocol. Distance vector routing protocols mathematically compare routes to determine the best path. IGRP was designed to take advantage of the simplicity of RIP and adds other metrics for best path selection and better scalability. The metrics available with IGRP are bandwidth, delay, load, reliability, and maximum transmission unit (MTU). These metrics can be used to make better mathematical decisions about best paths than the hop count metric used by RIP. By default, bandwidth and delay are the two metrics that are used and the others are set to zero. IGRP shares its routing information through the use of timed updates every 90 seconds.

Draw an example on the board to demonstrate how IGRP can make better routing decisions than RIP. There are three important points to emphasize:

• IGRP is Cisco proprietary. If students can select which routing protocols to use, the internetwork will have to be all Cisco devices for IGRP to be chosen.

• The default update time of IGRP is 90 seconds and the updates are broadcast.

• The default algorithms of IGRP are bandwidth and delay. The others can be used

if the algorithm is changed. MTU is only exchanged in the update. It is not used in any calculation.

One additional item to note is that Cisco offers more support for EIGRP than IGRP. Many of the newer releases of IOS do not support IGRP.

7.3.2 IGRP metrics

IGRP uses several metrics to calculate the overall routing metric of each route:

• Bandwidth – the lowest bandwidth value in a path

• Delay – the cumulative interface delay along a path

• Reliability – the reliability between source and destination, determined by the

exchange of keepalives

• Load – the load on a link between a source and a destination based on bits per second

• MTU – the maximum transmission unit value of a path

The show ip protocol command is used to display parameters, filters, and network information about the routing protocol used by a router. Each metric has a corresponding K value or weight. By default, only K1 and K3 are set to one. These represent the K values for bandwidth and delay. The K values of the other metrics are set to zero. By default, only bandwidth and delay are used to determine the composite metric or routing metric of each route. This use of multiple components to calculate a composite metric provides greater accuracy than the RIP hop-count metric to choose the best path.

The show ip route command displays the composite IGRP metric for a given route in brackets with the administrative distance. A link with higher bandwidth will have a lower metric. A link with lower cumulative delay will have a lower metric.

The lower the metric is, the better the route. Make sure that students understand that the default metrics for IGRP are bandwidth and delay. The other metrics can be used but are not used by default. Allow the students to configure IGRP on a mesh network and adjust the metrics to see how the routing table is changed. Students should also be instructed to trace the path to a network before and after the metric changes to verify the different path selection.

7.3.3 IGRP routes

IGRP advertises three types of routes:

• Interior

• System

• Exterior

Interior routes are defined as routes between subnets that are connected to the same router interface. System routes are routes within the same autonomous system. These routes are derived from directly connected networks and through routes learned from other IGRP routers. System routes do not contain subnet information. Exterior routes are routes between autonomous systems. A gateway of last resort can be used to transfer information to a destination outside of a local autonomous system.

Describe the graphic included in the TI in depth. Explain the concepts of interior routes and multiple subnets on the same router interface. Autonomous systems should also be explained.

7.3.4 IGRP stability features

Features designed to enhance the stability of IGRP consist of holddowns, spit horizons, and poison-reverse updates. Holddowns are used to prevent regular update messages from reinstating a route that is down. This is done through the lack of regularly scheduled update messages. If a router does not receive an update about a particular route, it marks that route as possibly down. Split horizons are designed to prevent routing loops with the rule that routing information is not sent back in the direction from which it was learned. This prevents routing loops between adjacent routers. Poison-reverse updates are necessary to avoid larger routing loops. An increase in metric may indicate a routing loop, so poison-reverse updates are sent to place the route with the increasing metric in holddown. IGRP sends out poisonreverse updates when the route metric has increased by a factor of 1.1 or more.

The timers associated with IGRP include update, invalid, hold-down, and flush timers. The update timer indicates how often routing updates will be sent, the default for IGRP is 90 seconds. The invalid timer is the amount of time that IGRP will wait before it declares a route invalid. The default for IGRP is 270 seconds, which is 3 times the update period. The holddown variable specifies the holddown period. During this period the information about better routes is suppressed, even though the route in holddown is marked as inaccessible and advertised as unreachable. When the holddown time has expired, routes advertised by other routers are accepted. The default holddown time is greater than three times the update time. The flush timer indicates the amount of time that a route should remain in the routing table before it is flushed. This time should be at least as long as the holddown and invalid times combined. This will allow the proper holddown phase, otherwise the route may be flushed and new routes may be accepted prematurely. The default flush timer is seven times the update time. The show ip protocol command should be used to view the timers and then timers should be changed and viewed again.

The debug ip igrp events command can be used to verify that the timers affect routing updates. Have the students configure IGRP on the lab topology.

7.3.5 Configuring IGRP

To enable IGRP routing use the router igrp as-number global configuration command. To disable IGRP routing use the no router igrp as-number command.

RouterA(config)#router igrp as-number RouterA(config-router)# RouterA(config)#no router igrp as-number RouterA(config)#

To identify which networks will participate in the IGRP routing process, use the network network-address router configuration command. To remove a network from the IGRP routing process, use the no network network-address command.

RouterA(config)#router igrp 101 RouterA(config-router)#network 192.168.1.0 RouterA(config)#router igrp 101 RouterA(config-router)#no network 192.168.1.0

The autonomous system number is used to identify the router to other IGRP routers and to tag routing information. Have the students configure IGRP on the lab topology.

7.3.6 Migrating from RIP to IGRP

With the creation of the IGRP in the early 80s, Cisco Systems was the first company to solve the problems associated with RIP. IGRP was designed to have a greater maximum hop count, which gave it more scalability for larger companies. IGRP uses multiple metrics to determine the best path, bandwidth, and delay, as opposed to the hop count metric used by RIP. As a result of these improvements, IGRP enabled many large, complex, and topologically diverse internetworks to be deployed. Have the students configure the lab topology with RIP and then migrate to IGRP. Make sure that students understand that RIP is still the most implemented routing protocol in smaller internetworks. Also, emphasize that IGRP can only be used in a fully Cisco environment.

7.3.7 Verifying IGRP Configuration

The following commands and available switches can be used to verify the configuration of IGRP:

• show interface

• show ip protocol

• show ip route

• show running-config

The show interface command can be used to verify issues that are specifically related to the interface configuration such as the ip address, physical connectivity, and keepalives. The show ip protocol command should be used to verify that routing protocols are correctly configured. This command can be used to view the routing protocols enabled on the router,

the networks advertised, timer values, and other routing protocol-specific information. The show ip route command displays the routing table and lists the next hop to all known networks, how the route was learned, the metric, and other route specific information. The show run command can be used to verify the running configuration. Have the students verify proper operation of IGRP on the lab topology.

7.3.8 Troubleshooting IGRP

Most of the IGRP configuration errors involve a bad network statement, discontiguous subnet, or incorrect autonomous system number. The following commands are used to troubleshoot IGRP:

• show ip protocols

• show ip route

• debug ip igrp events

• debug ip igrp transactions

• ping

• trace

Both the debug ip igrp events and debug ip igrp transactions commands can be used to verify that routing information is being passed between routers. The ping command can be used to test network connectivity. The trace command can be used to locate pinpoint delay or connectivity issues. Have the students take a break and place several IGRP problems on the lab topology. When the students return from the break, instruct them to troubleshoot the topology and correct any problems they find. Emphasize the fact that the show run command, which makes it easy to troubleshoot problems in a lab, may not be very effective in real situations. The show run command should be used to verify configuration changes.

Module 7 Summary

Before students begin Module 8, they must be able to configure and troubleshoot RIP and IGRP by themselves.

Online assessment options include the end-of-module online quiz in the curriculum and the online Module 7 exam. Formative skill assessments such as timed competitions to see who can get hands-on or e-Lab routing to work the fastest should be used. The emphasis of any assessment should be on the ability to demonstrate mastery.

Students should understand the following main points:

• How routing information is maintained through distance vector protocols

• How routing loops occur in distance vector

• How to define a maximum to prevent count to infinity

• How to eliminate routing loops through split horizon

• Route poisoning

• How to avoid routing loops with triggered updates

• How to prevent routing loops with holddown timers

• How to prevent routing updates through an interface

• Load balancing across multiple paths

• RIP process

• RIP configuration

• The ip classless command

• Common RIP configuration issues

• Load balancing with RIP

• How to integrate static routes with RIP

• How to verify RIP configuration

• IGRP features

• IGRP metrics

• IGRP routes

• IGRP stability features

• How to configure IGRP

• How to migrate RIP to IGRP

• How to verify IGRP configuration

• How to troubleshoot IGRP

Module 8: TCP/IP Suite Error and Control Messages

Overview

The main goal of Module 8 is for students to learn how the IP protocol uses the ICMP protocol to provide control messages to hosts on a network. IP does not have the facilities to send error messages. It uses ICMP to send, receive, and process error and control messages.

Module 8 Caution Error and control messaging is an important aspect of TCP/IP. Make sure the students

understand that ICMP is the protocol that handles these functions for the TCP/IP suite. If time is an issue, this module can be used as a reference for other modules when students encounter different ICMP error messages in their labs and in their use of programs such as browsers and e-mail.

Students who complete this module should be able to perform the following tasks:

• Describe ICMP

• Describe the ICMP message format

• Identify ICMP error message types

• Identify potential causes of specific ICMP error messages

• Describe ICMP control messages

• Identify a variety of ICMP control messages that are used in networks

• Determine the causes for ICMP control messages

8.1 Overview of TCP/IP Error Message

Essential Labs: None Optional Labs: None Core TIs: 8.1.1, 8.1.2, 8.1.4, 8.1.5, 8.1.6, and 8.1.8 Optional TIs: 8.1.3, 8.1.7, and 8.1.9 Course-Level Claim: Students can describe the operation of ICMP and identify the reasons,

types, and format of associated error and control messages.

Hands-on skills: none

8.1.1 ICMP

IP is considered a “best effort” or unreliable method for the delivery of network data. If the data does not reach its destination, the sender is not notified that the transmission has failed. ICMP is the component of the TCP/IP protocol stack that addresses the limitations of IP. ICMP does not overcome the unreliability issues in IP but ICMP does allow for testing. Reliability must be provided by upper layer protocols. Explain the difference between a guaranteed method and a best effort. This is a good time to show students how a successful ICMP works. Introduce problems into the lab setup to demonstrate how ICMP relays messages in a network. Explain that ICMP is a Layer 3 protocol of the TCP/IP suite. It is not an IP packet. It uses the IP addressing scheme but has a different packet format than IP.

8.1.2 Error reporting and error correction

ICMP is an error reporting protocol for IP. When datagram delivery errors occur, ICMP is used to report these errors back to the sender of the datagram.

This is an excellent opportunity to show the students this procedure in the lab setup. They should be shown that ICMP does not correct the encountered network problem. ICMP just reports on the status of the delivered packet to the sender. Its function is not to propagate information about network changes.

8.1.3 ICMP message delivery

ICMP is a message protocol for TCP/IP protocol suite. ICMP messages are encapsulated as data in ICMP packets in the same way that IP data is delivered. ICMP messages have their own header information. They are subject to the same failures as any other data. The students should realize that ICMP is a Layer 3 protocol that does not use IP packets. ICMP uses IP addressing but has a different structure than an IP packet. Show the students that this scenario could generate more error reports and cause increased congestion on an already ailing network. For this reason, errors created by ICMP messages do not generate their own ICMP messages. Stress to the students that it is possible to have a datagram delivery error that is never reported back to the sender of the data.

8.1.4 Unreachable networks

Network communications depend on certain basic conditions:

• The sending and receiving devices must have the TCP/IP protocol configured.

• This includes a correct IP address and subnet mask.

• A default gateway must be set if data will go outside the LAN.

• Devices must be place to route the data.

• The router must be configured correctly and the correct routing protocol must be

used.

If these conditions are not met, communication cannot occur. Instruct the students to discuss problems that could cause a network to be unreachable.

8.1.5 Using ping to test destination reachability

The ICMP protocol can be used to test the availability of a destination. If a destination receives the ICMP echo request, it formulates an echo reply to send back to the source. If the sender receives the echo reply, this confirms that the destination can be reached. The process is initiated with the ping command.

Have the students do an exercise on the ping procedure. Discuss the use of the DNS function. Explain that the DNS must be available to use a domain name instead of an IP address when the ping command is used. Also point out that a way to check the function of DNS is to ping the same destination by domain name and by IP address. If the remote location responds to the IP address but not to the domain name then this indicates a DNS issue. Explain that a location may be unreachable because of security restrictions. ICMP may be a blocked protocol.

8.1.6 Detecting excessively long routes

Situations in a network can occur where datagrams travel in a circle and never reach their destination. This could occur because no path exists between a source and a destination that conforms to the requirements of the routing protocol. This could be caused by incorrect routing information. Explain that paths with too many hops and circular paths create an excessively long route. The packet will eventually reach the end of its life, known as time to live (TTL). The TTL is not related to the hop count value of RIP. RIP advertisements are broadcast. That means they will not go farther than the local segment. The reachability of RIP is controlled by the routing protocol. It maintains a hop count metric that cannot exceed 15. This means that a route will not be advertised further than 15 hops. It does not mean that packets cannot travel more than 15 hops. The process is as follows:

1. As each router processes the datagram, the TTL value decreases by one.

2. When the TTL value reaches zero, the packet is discarded.

8.1.7 Echo messages

ICMP message formats have three fields:

• Type

• Code

• Checksum

The type field indicates the type of ICMP message that is sent. The code field includes additional information that is specific to the message type. The checksum field is used to verify the integrity of the data. Create an example to help students understand this format. This is an important concept to help the student understand causes of ICMP "destination unreachable" messages.

8.1.8 Destination unreachable message

Hardware failures, improper protocol configuration, disabled interfaces, and incorrect routing information are some of the reasons for unsuccessful delivery of data. Give the students examples similar to the figures in the curriculum. Specify values and indicate the reason for each failure. Explain that the students must understand the various causes of ICMP "destination unreachable" messages to effectively troubleshoot an IP network.

8.1.9 Miscellaneous error reporting

Devices that process datagrams may not be able to forward a datagram due to some type of error in the header. The error does not relate to the state of the destination host or network, but it will still prevent the datagram from being processed and delivered.

8.2 TCP/IP Suite Control Messages

Essential Labs: None Optional Labs: None Core TIs: None Optional TIs: All Course Level Claim:

types, and format of associated error and control messages. Hands-on skills: none

Students can describe the operation of ICMP and identify the reasons,

8.2.1 Introduction to control messages

ICMP is an integral part of the TCP/IP protocol suite. All IP implementations must include ICMP support for the following reasons:

• Since IP does not guarantee delivery, it has no method to inform hosts when errors occur.

• IP has no built-in method to provide information or control messages to hosts.

• ICMP is necessary to perform these functions for IP.

Explain to the students that unlike error messages, control messages are not the result of lost packets or error conditions. Instead, they are used to inform hosts of conditions such as network congestion or the existence of a better gateway to a remote network. Like all ICMP messages, ICMP control messages are encapsulated.

8.2.2 ICMP redirect/change requests

An ICMP redirect/change request can only be initiated by a gateway, which is commonly used to describe a router. All hosts that communicate with multiple IP networks must be configured with a default gateway. This default gateway is the address of a router port connected to the same network as the host. Normally there is a single gateway. In some circumstances a host can connect to a segment that has two or more directly connected routers. In these situations, the default gateway may need to use a redirect/change request to inform the host of the best path. Explain this concept with the students and make sure they understand this important process.

Default gateways only send ICMP redirect/change requests if the following conditions are met:

• The interface on which the packet comes into the router is the same interface on which the packet gets routed out.

• The subnet/network of the source IP address is the same subnet/network of the next hop IP address of the routed packet.

• The datagram is not source-routed.

• The route for the redirect is not another ICMP redirect or a default route.

• The router is configured to send redirects.

Make sure students understand default gateways. Instruct students to look at the router lab setup and visually determine the default gateway of the host attached to it.

8.2.3 Clock synchronization and transit time estimation

Networks that connect to each other over vast distances choose their own method of clock synchronization. As a result, hosts on disparate networks who attempt to communicate with software that requires time synchronization can encounter problems. The ICMP timestamp message type is designed to help alleviate this problem.

The ICMP timestamp request message allows a host to ask the remote host for the current time. The remote host uses an ICMP timestamp reply message to respond to the request. The type field on an ICMP timestamp message can be either a 13 or 14 timestamp reply. The code field value is always set to zero. The ICMP timestamp request contains an originate timestamp, which is the time on the requesting host just before the timestamp request is sent. The receive timestamp is the time that the destination host receives the ICMP timestamp request. The transit timestamp is filled in just before the ICMP timestamp reply is returned. Originate, receive, and transit timestamps are computed in numbers milliseconds elapsed since midnight (00:00), Universal Time.

The host that originated the ICMP timestamp request can use these timestamps to estimate transit time across the network. The host can subtract the originate time from the transit time to guess the transit time. However this can vary widely based on traffic and congestion. The host that originated the ICMP timestamp request can also estimate the local time of the remote computer. This is an important concept for the students to understand. Make sure that they also understand that NTP, which is a UDP protocol, is used to maintain the time between systems.

8.2.4 Information requests and reply message formats

ICMP information requests and reply messages were originally intended to allow a host to determine the number of the network it resided on. However, BOOTP and DHCP are now used to allow hosts to obtain the network number to which they are attached.

8.2.5 Address mask requests

A subnet mask is important to identify network, subnet, and host bits in an IP address. If a host does not know the subnet mask, it may send an address mask request to the local router. The router responds with an ICMP address mask reply. If the address of the router is known, this request may be sent unicast. If the address is not known, the request will be a broadcast. When the router receives the request, it will respond with an address mask reply. This reply will identify the correct subnet mask. This is an important concept for the students to understand. This is also a good time to review IP addressing.

8.2.6 Router discovery message

When a host on a network boots and has not been manually configured with a default gateway, it can learn the available routers through the process of router discovery. This

process begins when the host sends a multicast router solicitation message to all routers with the address 224.0.0.2. If a router solicitation message is sent to a router that does not support the discovery process, the solicitation will go unanswered. However, if it is supported, a router advertisement is sent in return.

8.2.7 Router solicitation message

A host will generate an ICMP router solicitation message in response to a missing default gateway. This message is sent multicast. This is the first step in the router discovery process. A local router will respond with a router advertisement that identifies the default gateway for the local host.

8.2.8 Congestion and flow control messages

Congestion occurs when multiple computers try to access the same receiver or when traffic from a high speed LAN reaches a slower WAN connection. The effect of congestion on a network is dropped packets that result in a loss of data. To reduce data lost, ICMP messages must be sent to the source of the congestion. This type of ICMP message is called a sourcequench message. The source-quench message notifies the sender of the congestion and asks the sender to reduce its rate. This usually reduces the congestion. The rate of transmission will slowly increase if no other source-quench messages are received. One way ICMP sourcequench messages might be used effectively is in a SOHO. Develop an example of network congestion. Have the students come up with their own ideas about the factors that cause network congestion.

Cisco Systems CCNA 2 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

I. Welcome

II. Course Overview

III. Teaching Guide for Each TI

Module 1: WANs and Routers

1.1 WANs

1.2 Routers

Module 1 Summary

Module 2: Introduction to Routers

2.1 Operating Cisco IOS Software

2.2 Starting a Router

Module 2 Summary

Module 3: Configuring a Router

3.1 Configure a Router

3.2 Finishing the Configuration

Module 3 Summary

Module 4: Learning about Other Devices

4.1 Discovering and Connecting to Neighbors

4.2 Getting Information about Remote Devices

Module 4 Summary

Module 5: Managing Cisco IOS Software

5.1 Router Boot Sequence and Verification

5.2 Managing the Cisco File System

Module 5 Summary

Module 6: Routing and Routing Protocols

6.1 Introduction to Static Routing

6.2 Dynamic Routing Overview

6.3 Routing Protocols Overview

Module 6 Summary

Module 7: Distance Vector Routing Protocols

7.1. Distance Vector Routing

7.2 RIP

7.3 IGRP

Module 7 Summary

Module 8: TCP/IP Suite Error and Control Messages

8.1 Overview of TCP/IP Error Message

8.2 TCP/IP Suite Control Messages