Linear methods of troubleshooting are often split into two main areas, bottom-up and top-down approaches. Both have advantages and disadvantages and can be used in differing situations as outlined previously.

Bottom-Up Approach

The bottom-up approach to troubleshooting a computer problem would start with the physical components and works up the applications layer. Bottom-up troubleshooting is an effective and efficient approach for situations when the problem is suspected to be physical. Physical problems are usually fairly easy to rule out and can save you time troubleshooting other higher-level issues. For example, if the cable is unplugged, it does not make sense to spend time trying to determine network access by using traceroute or ping commands.

Top-Down Approach

When you apply a top-down approach to troubleshooting a networking problem, you start with the user application and work your way down the layers of the OSI model. The top-down approach is usually the simple route and typically affects only one or a few users. Lower layers, or network infrastructure, usually affect more than a few users.

For example, if a user cannot get to a website, the technician can start at the top of the OSI model and try accessing a different website. If the other website can be accessed, the problem is probably with the first website. If the second site is also inaccessible, the technician can move down the OSI model and check for a firewall blocking ports at the transport layer. The technician could then check IP settings on the host and try pinging the default gateway or the DNS servers to determine if the problem is at the network layer.

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