9: Troubleshooting Your Network

Networking for Home & Small Business

I Want My Network!

• Troubleshooting process

• Utilities for connectivity tests

• Common hardware & connection issues

• Working with the help desk

Troubleshooting

• Identifying, locating and correcting problems

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

• Take documentation– The problem encountered – Steps taken to determine the cause of the problem – Steps to correct the problem and ensure that it will not

reoccur

Step 1

• Verify problem & GATHER INFO– Question users

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

– 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

Why do this?

• 90% of your job!!!– JOB SECURITY– Keeps users happy when working

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

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?

• Now compare to the OSI model

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

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?

Activity

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

• 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)

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

• 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?

More Issues

• Wired & Wireless

• Ping from each to DG & to each other

• Check the Router

Router/AP

• Check the LED

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?

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

9: Troubleshooting Your Network

Networking for Home & Small Business