Fundamentals of NetworkingDiscovery 1, Chapter 9Troubleshooting

Objectives

•Describe the troubleshooting process

•Describe the utilities used to verify TCP/IP connectivity

• Identify & describe common hardware and connection issues in wired and wireless networks

•Use the troubleshooting process to document problems and interact with a help desk

Troubleshooting

Process

Troubleshooting• Identifying, locating and correcting problems

•Not a trial & error!▫Too much wasted time

•Take documentation▫The problem▫ Steps taken to determine the cause of the problem ▫ Steps to correct the problem & ensure it won’t reoccur▫ Solutions that didn’t work▫ Solution that does work

Effective Troubleshooting

•90% of your job!!!▫JOB SECURITY if you do it good▫Keeps users happy when working

• If you get a help desk call…▫You need a plan!

Step 1: Gather Info• Verify problem• GATHER INFO▫Question users

What happened? Any error messages? What web site did you type in?

• COLLECT INFO ▫What equipment is involved?

Any recent changes to config? Gather brand/model, warranty info

▫Gather network info In you have tools, monitor network for errors

Scenario

•PC is down.•Need to finish sales report they were working on &

it’s due at 11am. ▫Now what???▫What could the problems be?

•Ask questions, narrow choices

Troubleshooting Method 1

•Top-down ▫Application layer down

Starts near the user▫Looking for problems in applications

Maybe a configuration problem in IE▫Is it just one application that is not functioning, or do

all applications fail? For example, can the user access various web pages on

the Internet, but not email? Do other workstations have similar issues?

Troubleshooting Method 2

•Bottom-up ▫Starts at Physical layer & then up▫Good for novice▫Could take longer to solve problems▫Hardware & wires▫Have cables been pulled out of their sockets?▫If the equipment has indicator lights, are they on or

off?

Troubleshooting Method 3

•Divide-and-conquer▫More experienced people

▫Start at middle layers & work up/down from there Check IP address, default gateway

Troubleshooting Method 4

•Trial & Error▫Make an educated guess based on past experience▫If doesn’t work, you use that info to try something else▫Relies on your abilities & experience

This actually could slow you down

Troubleshooting Method 5•Substitution▫Problem is specific to a piece of hardware▫Can save time for user▫You must have the available parts

Could be expensive Doesn’t always happen

At Home

•Would you keep spare equipment, like an extra router?

•Would you be running network monitors?

•Should you keep documentation of problems, upgrades & software versions?

Question

•You get a call from your boss saying that he can not get access to the McDonalds web site. Which option would you do first?▫Call McD’s & ask them to reboot their web server. ▫Get the boss a new NIC. ▫Have the boss to log off and log on again. ▫Ask the boss to read the web address he typed and

what error message displayed.

Activity

Review

•You complain to Comcast about connectivity issues. They are sending you a new cable modem. Which troubleshooting process is this?▫Substitution

•Bob’s PC is the only one in the office that can’t connect to the Internet. You are smart & use Divide & Conquer. What would you check first?▫IP address configuration

Review

•Which of these would be best for a home network?▫Having an extra Linksys router as backup▫Keeping spare wireless cards handy▫Keeping a backup of ISR configuration

•Which of these is a physical layer problem?▫Loose connectors▫Wrong IP address▫Driver not installed

Troubleshooting

Issues

Let’s Get Physical!

•Many problems are hardware related•Use your senses▫Vision, smell, touch and hearing

Utilities!

Could it be a DHCP issue?

• Ipconfig• Ipconfig /all, release, renew

Activity- Using ipconfig

•Packet Tracer Lab, 9.2.3.2

May I Ping You?

•Ok, you have an IP▫Can you ping something?▫Can also test DNS (ping www.cisco.com)▫Echo request & reply

Now What?•You have an IP•You can ping the destination•Must be a problem in the application▫ Like IE

•You have an IP•You can NOT ping•Start pinging closer to you▫Try default gateway 1st

▫YES: problem in not local▫NO: problem is in local network

Ping Example

Ping Options

Activity- Using Ping

•Packet Tracer Lab 9.2.4.3

Tracert

•Shows path of routers (hops)•Can identify where the error is•30 hops max; you can change▫-h

Netstat

•Shows protocols used, port number, local & foreign address

Nslookup

• Is the DNS server properly translating names to IP addresses?

Connectivity

Issues

More Issues

•Wired & Wireless▫Is the problem the wired or wireless?

•Ping from each PC to DG & to each other

•Check the Router

Router/AP

•Check the LED or status page

Check the Cables!

•Straight-through, crossover?•Bad connection?•Too long?

What’s Wrong Here?

WLAN Problems•a/b/g/n compatibility•Signal strength• Interference•SSID, Authentication, Encryption= MATCH!▫SSID case sensitive▫Keys don’t match

•# of clients to channels

•Do 9.3.4.2 & 9.3.5.2 Packet Tracer

What’s Wrong Here?

Activity

Your LAN works, but…

•No ISP connection•Check modem•Ping web site•Ping another web site•Are any access-lists set up?

Review

• Identify what each test does.▫Ping▫Tracert▫Nslookup▫Ipconfig

•Something’s wrong. You check the cables first and they are bad. Which troubleshooting method did you use?▫Bottom-up

Review

•The Linksys ISR is showing a blinking green LED on #1. What does that mean?▫Activity…good!

Troubleshooting

& the Help Desk

SOS

•Other resources of help

Help Desk

•Provides assistance to determine if a problem exists, the nature of the problem, and the solution.

•Can run remote diagnostics

•Get all their info & document▫What solved problem▫What steps worked & didn’t work

Baseline

•When it all works…▫Establish a baseline

What is normal traffic, etc.▫Document it

▫After you make network changes, test again Re-document the baseline

Review- 10 Questions

Fundamentals of NetworkingDiscovery 1, Chapter 9Troubleshooting