Ca Ex S4 C8 Network Troubleshooting

transcript

CCNA – Semester 4

Chapter 8: Network Troubleshooting

CCNA Exploration 4.0

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.

Establishing the

Network Performance Baseline

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

Network configuration table

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

software used in a network.

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.

Network Topology Diagram

• Graphical representation of a network, which illustrates how

each device in a network is connected and its logical

architecture.

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

Why Is Establishing a Network Baseline

Important?

Steps for Establishing a Network Baseline

• Planning for the First Basline

• Step 1. Determine what types of data to collect

• Step 2. Identify devices and ports of interest

• 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.

Measuring Network Performance Data

• Automated Data Collection: Fluke Network SuperAgent

module

Measuring Network Performance Data

• Manual Commands

Troubleshooting Methodologies and

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.

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.

Using Layered Models for Troubleshooting

• OSI Versus TCP/IP Layered Models

General Troubleshooting Procedures

• General troubleshooting process:

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.

• 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.

• Guidelines for Selecting a Troubleshooting Method

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

Gathering Symptoms

• Use the Cisco IOS commands to gather symptoms about the

network.

Gathering Symptoms

• Questioning End Users

Software Troubleshooting Tools

• NMS Tools

• Knowledge Bases

• Baselining Tools

• Protocol Analyzers

Hardware Troubleshooting Tools

• Network Analysis Module (NAM)

Digital Multimeters Cable Testers

Cable Analyzers Portable Network Analyzers

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

Common WAN Implementation Issues

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

Steps in WAN Design

LOCATE LANs

ANALYZE TRAFFICS

PLAN TOPOLOGY

PLAN BANDWIDTH

CHOOSE

TECHNOLOGY

COST AND EVALUATE

IterateReview

WAN Traffic Considerations

WAN Topology Considerations

Star or Hub-and-SpokeFull-Mesh

Partial-Mesh

WAN Connection Technologies

WAN Topology Considerations

WAN Bandwidth Considerations

Common WAN Implement Issues

Case Study: WAN Troubleshooting from a

ISP’s Perspective

Network Troubleshooting

Interpreting Network Diagrams to Identify

Problems

Interpreting Network Diagrams to Identify

Problems

Physical Layer Troubleshooting

• Troubleshooting

Layer 1 Problems

Data Link Layer Troubleshooting

Troubleshooting Layer 2 - PPP

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

both ends

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

negotiations have succeeded

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

Troubleshooting Layer 2 – Frame Relay

• Step 1: Verify the physical connection between the

CSU/DSU and the router.

• Step 2: Verify proper LMI information exchange between

each router and the FR switch.

• Step 3: Verify that PVC status is active

• Step 4: Verify that Frame Relay encapsulation matches on

both routers

Troubleshooting Layer 2 - STP Loops

Network Layer Troubleshooting

Transport Layer Troubleshooting

Application Layer Troubleshooting

Activity: 8.4.6.5

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.

Ca Ex S4 C8 Network Troubleshooting

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