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The Best Way to Troubleshoot Computers and Networks

Posted on March 23rd, 2009 by Eric English 2 Comments »

Eric EnglishSo what is the best way to troubleshoot computers and/or networks? I think everyone has their own strategy for troubleshooting, but what if you’re new to IT and don’t know where to start?

Well, it’s time to bust out your books from school and start putting the theory you learned to good use. Do you remember learning about the OSI model and the 7 layers? Let’s see how you can use the OSI model or a custom strategy to help you troubleshoot your computers and/or network.

 

Troubleshooting with the OSI Model

The OSI Model is a way of dividing network framework into 7 layers to help create a visual model of networking and protocols. Each layer has its own function and supports the layer under it and/or above it. From top to bottom the layers are:

  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data-link
  • Physical

When troubleshooting, it’s best to start from the top or the bottom and work your way through the layers.


For instance, if you notice that a cable is unplugged while you are troubleshooting, you want to start at the physical layer and work your way up. If the user reports they have a problem with a Word document you probably want to start at the Application layer.

 

Layered Troubleshooting

 

• Application Layer

This layer is used as a means of communication between the operating system, the application, and the end user. So basically how programs talk to your operating system.

An example of this could be a program that doesn’t function like it normally would, or if you get error messages when you run your program, or maybe it won’t let you save your work. This would be an application layer issue and that is where you should start your troubleshooting efforts.

Some of the protocols used at this layer are SMB, FTP, AFP, TELNET, SMTP, and DNS.

• Presentation Layer

The Presentation layer is used to create a standard for communication between the application and network formats. In other words, this is the translator.

This layer handles encryption, data compression and a few other things. An example of this layer is your wireless router at home using WEP, WPA or another type of encryption. The Presentation layer is translating the encryption on your wireless network.

• Session Layer

The Session layer is used to create and manage sessions across a network.

An example of this would be Remote Desktop. If a user reported they were unable to connect to your application server using Remote Desktop, then you might want to start your efforts at this layer.

NetBIOS and RPC are some of the protocols used on this layer.

• Transport Layer

Think of the Transport layer as a taxi driver. His or her job is to get you where you need to go and to make sure you arrive safely.

The Transport layer provides flow control and error handling on a network. Like the taxi driver making sure you arrive safely, the Transport layer makes sure that all transmissions were successful. If you get into a wreck in the taxi, that’s an error by the taxi driver!

The Transport layer also makes sure that all packets and transmissions are error free. Some of the protocols used on this layer are TCP, NetBIOS, RARP, ARP, and NetBEUI.

• Network Layer

This layer handles network addressing and routing. It translates IP addresses into MAC addresses, or computer names to MAC addresses. In a nutshell you would be troubleshooting mostly routers on the Network layer.

• Data-link Layer

The Data-Link layer is used to turn packets into bits, and vice versa. This layer also transmits data across a physical network link. Common devices on this layer are hubs, switches, NICs, and bridges.

• Physical Layer

I personally start at the physical layer most of the time because that is where I tend to find the majority of the issues. "The cleaning person knocked a cable lose" or "I moved my tower to the other side of my desk".

The physical layer includes making a physical connection, physical cabling, or even a radio link.

It is good to be familiar with the OSI model and what protocols and equipment work on each layer. This helps you troubleshoot the root of the problem and gives you a very logical approach to troubleshooting.

 

Other Troubleshooting Methods

That’s just one of the ways to troubleshoot your computers or networks, but there are many other ways to go about it. How about making up your own troubleshooting steps for your specific environment?

Here are some ideas for your own troubleshooting steps.

  1. Figure out the real problem — This always seems to elude IT people when getting phone calls from users. "My computer is broken" or "My printer doesn’t print" are the typical issues users report, so digging around for clues to figure out more information is always a good idea. We need to get as much information from the users as possible so that we can determine the point of failure.

  2. Create a plan to resolve the problem — Now that we have more info from the users we can move forward and create a plan of action. Decide the best ways to go about implementing your plan of action and make sure to explore all possibilities to come up with the best solution.

  3. Implement — This is where the rubber meets the road and you will need to put you plan into action.

  4. Revisit and revise — Revisit the user after implementing your strategy and make sure the issue is resolved. If not, revise your plan of action accordingly.

  5. Document — Document the final resolution for the issue for future reference.

 

Conclusion

There are many different ways to troubleshoot your computers and networks. You can use the 7 layer approach or create your own way of troubleshooting. There might even be a separate way of troubleshooting for your specific environment.

What other ways can you think of to troubleshoot computers and networks?

 


 

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2 Responses to “The Best Way to Troubleshoot Computers and Networks”

  • Adam Ruth Says:

    March 23rd, 2009 at 3:12 pm

    Great article, I’ll be using this in the future. I’ve learned to do this through practice, but I never thought about how the troubleshooting mapped to OSI layers. Makes sense.

    I think of troubleshooting as horizontal and vertical. Vertical troubleshooting is what you describe here. Horizontal is finding which node is the problem. I usually start with the horizontal and narrow down where to start the vertical.

    Does a ping return from this machine and not that? Is it the switch, the local network connection, or the router? Are pings working but not name resolution? Hopefully that’ll tell me which node is the bad actor.

  • Eric English Says:

    March 23rd, 2009 at 4:10 pm

    Thanks for reading Adam. That’s a great idea for troubleshooting. Use whatever makes most sense to you, or like you did, create your own way of troubleshooting.

    Thanks again for reading.

    Eric

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