Ca Ex S4 C8 Network Troubleshooting

CCNA – Semester 4

Chapter 8: Network Troubleshooting

CCNA Exploration 4.0

2

Objectives

• Establish and document a network baseline.

• Describe the various troubleshooting methodologies and

troubleshooting tools.

• Describe the common issues that occur during WAN

implementation.

• Identify and troubleshoot common enterprise network

implementation issues using a layered model approach.

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Establishing the

Network Performance Baseline

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Documenting Your Network

• To efficiently diagnose and correct network problems, a

network engineer needs to know how a network has been

designed and what the expected performance for this

network should be under normal operating conditions. This

information is called the network baseline.

• Network documentation should include these components:

– Network configuration table

– End-system configuration table

– Network topology diagram

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Network configuration table

• Contains accurate, up-to-date records of the hardware and

software used in a network.

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End-system Configuration Table

• Contains baseline records of the hardware and software used in end-system devices such as servers, network management consoles, and desktop workstations.

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Network Topology Diagram

• Graphical representation of a network, which illustrates how

each device in a network is connected and its logical

architecture.

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Network Documentation Process

• When you document your network, you may have to gather

information directly from routers and switches. Commands

that are useful to the network documentation process

include:

– The ping command

– The telnet command

– The show ip interface brief command

– The show ip route command

– The show cdp neighbor detail command

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Why Is Establishing a Network Baseline

Important?

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Steps for Establishing a Network Baseline

• Planning for the First Basline

• Step 1. Determine what types of data to collect

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• Step 2. Identify devices and ports of interest

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• Step 3. Determine the baseline duration

It is important that the length of time and the baseline

information being gathered are sufficient to establish a

typical picture of the network.

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Measuring Network Performance Data

• Automated Data Collection: Fluke Network SuperAgent

module

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Measuring Network Performance Data

• Manual Commands

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Troubleshooting Methodologies and

Tools

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A General Approach to Troubleshooting

• Network engineers, administrators, and support personnel

realize that troubleshooting is a process that takes the

greatest percentage their time.

• Two extreme approaches to troubleshooting almost always

result in disappointment, delay, or failure.

– The theorist, or rocket scientist, approach

– The impractical, or caveman, approach.

• The rocket scientist: analyzes and

reanalyzes the situation until the exact

cause at the root of the problem has

been identified and corrected with

surgical precision.

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A General Approach to Troubleshooting

• The caveman: first instinct is to start

swapping cards, cables, hardware, and

software until miraculously the network

begins operating again.

• Since both of these approaches are

extremes, the better approach is

somewhere in the middle using elements

of both. It is important to analyze the

network as a whole rather than in a

piecemeal fashion. A systematic

approach minimizes confusion and cuts

down on time otherwise wasted with trial

and error.

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Using Layered Models for Troubleshooting

• OSI Versus TCP/IP Layered Models

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General Troubleshooting Procedures

• General troubleshooting process:

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Troubleshooting Methods

• There are three main methods for troubleshooting networks:

– Bottom up

– Top down

– Divide and conquer

• Bottom-Up Troubleshooting Method

– Good approach to use when the

problem is suspected to be a

physical one.

– Disadvantage: requires checking

every device and interface

until the possible cause of the

problem is found.

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• Top-Down Troubleshooting Method

– Use for simpler problems or when

you think the problem is with a piece

of software.

– Disadvantage: requires checking

every network application until the

possible cause of the problem is

found.

• Divide-and-Conquer Troubleshooting

Method

– You select a layer and test in both

directions from the starting layer.

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• Guidelines for Selecting a Troubleshooting Method

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Gathering Symptoms

• Step 1. Analyze existing symptoms

• Step 2. Determine ownership

• Step 3. Narrow the scope

• Step 4. Gather symptoms from suspect devices

• Step 5. Document symptoms

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Gathering Symptoms

• Use the Cisco IOS commands to gather symptoms about the

network.

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Gathering Symptoms

• Questioning End Users

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Software Troubleshooting Tools

• NMS Tools

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• Knowledge Bases

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• Baselining Tools

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• Protocol Analyzers

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Hardware Troubleshooting Tools

• Network Analysis Module (NAM)

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Digital Multimeters Cable Testers

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Cable Analyzers Portable Network Analyzers

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Research Activity

• Software Tools– Network Management Systems:

• http://www.ipswitch.com/products/whatsup/index.asp?t=demo

• http://www.solarwinds.com/products/network_tools.aspx

• http://h20229.www2.hp.com/products/cvnnm/ds/cvnnm_ds.pdf

– Baselining Tools:

• http://www.networkuptime.com/tools/enterprise/

• http://www.neon.com/Tutorials/index.html?drawyournetworkmap.htm

– Knowledge Bases:

• http://www.cisco.com

– Protocol Analyzers:

• http://www.flukenetworks.com/fnet/en-us/products/OptiView+Protocol+Expert/

• Hardware Tools– Cisco Network Analyzer Module (NAM):

• http://www.cisco.com/en/US/docs/net_mgmt/network_analysis_module_software/3.5/user/guide/user.html

– Cable Testers:

• http://www.flukenetworks.com/fnet/en-us/products/CableIQ+Qualification+Tester/Demo.htm

– Cable Analyzers:

• http://www.flukenetworks.com/fnet/en-us/products/DTX+CableAnalyzer+Series/Demo.htm

– Network Analyzers:

• http://www.flukenetworks.com/fnet/en-us/products/OptiView+Series+III+Integrated+Network+Analyzer/Demos.htm

http://h20229.www2.hp.com/products/cvnnm/ds/cvnnm_ds.pdf

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Common WAN Implementation Issues

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WAN Communications

• A communications provider

owns the data links that make

up a WAN.

• Speed (BW) is considerably

slower than LAN bandwidth.

• WANs carry a variety of traffic types, such as data, voice,

and video.

• Older WANs often consisted of data links directly connecting

remote mainframe computers.

• Today's WANs connect geographically separated LANs.

WAN technologies function at the lower three layers of the

OSI reference model

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Steps in WAN Design

LOCATE LANs

ANALYZE TRAFFICS

PLAN TOPOLOGY

PLAN BANDWIDTH

CHOOSE

TECHNOLOGY

COST AND EVALUATE

IterateReview

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WAN Traffic Considerations

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WAN Topology Considerations

Star or Hub-and-SpokeFull-Mesh

Partial-Mesh

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WAN Connection Technologies

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WAN Topology Considerations

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WAN Bandwidth Considerations

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Common WAN Implement Issues

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Case Study: WAN Troubleshooting from a

ISP’s Perspective

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Network Troubleshooting

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Interpreting Network Diagrams to Identify

Problems

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Interpreting Network Diagrams to Identify

Problems

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Physical Layer Troubleshooting

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• Troubleshooting

Layer 1 Problems

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Data Link Layer Troubleshooting

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Data Link Layer Troubleshooting

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Troubleshooting Layer 2 - PPP

• Step 1: Check that the appropriate encapsulation is in use at

both ends

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• Step 2: Confirm that the Link Control Protocol (LCP)

negotiations have succeeded

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• Step 3: Verify authentication on both sides of the link

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Troubleshooting Layer 2 – Frame Relay

• Step 1: Verify the physical connection between the

CSU/DSU and the router.

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• Step 2: Verify proper LMI information exchange between

each router and the FR switch.

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• Step 3: Verify that PVC status is active

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• Step 4: Verify that Frame Relay encapsulation matches on

both routers

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Troubleshooting Layer 2 - STP Loops

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Network Layer Troubleshooting

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Network Layer Troubleshooting

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Transport Layer Troubleshooting

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Application Layer Troubleshooting

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Activity: 8.4.6.5

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Summary

In this chapter, you have learned to:

• Establish and document a network baseline.

• Describe the various troubleshooting methodologies and

troubleshooting tools.

• Describe the common issues that occur during WAN

implementation.

• Identify and troubleshoot common enterprise network

implementation issues using a layered model approach.

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Ca Ex S4 C8 Network Troubleshooting

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