Troubleshooting Methodologies and Tips

You've got an issue with your wireless link, network, or WiFi and people are starting to complain...

"WHAT SHOULD I DO?...."

First of all, don't panic. You've got this! Secondly, this blog is here to help.

This blog will go through different methodologies to troubleshooting issues on your network/devices. We will demonstrate these with examples we have seen when providing support to our customers.

Methodologies

Before we look at methodologies we first must understand one of the main concepts of TCP/IP networking, the OSI model.

OSI Model

The OSI model is used to describe the functions at each layer of the TCP/IP stack. There are 7 layers and these are: 

As there are plenty of resources online, I won't go into too much detail here but let's cover the commonly examined layers:

Layer 7: This layer provides services to the end user such as DNS, DHCP, and HTTP

Layer 4: Provides end to end connectivity via TCP or UDP

Layer 3: Provides logical addressing to devices via IPv4/IPv6 and determines the best path a packet should take

Layer 2: Provides physical addressing via MAC and determines how to send frames on a network

Layer 1: Specifies the network hardware, such as ethernet or wireless media

Please do take the time to look into these further when you have a chance as knowledge of TCP/IP is vital to modern networking.

Common Troubleshooting Techniques

The three techniques we will look at in this blog are: top-down, bottom-up and best guess.

Top-Down

The top-down method entails beginning at the higher layers of the OSI model. 

An example of this would be ensuring services like DNS or DHCP are properly configured on networking hardware and client devices. A more advanced example would be inspecting TCP session establishment in routing protocols such as BGP.

Real life scenario: "I can ping my default gateway but I can't open any web pages"

Bottom-Up

The bottom-up method starts at the opposite end of the OSI model at the physical layer. An example of this approach usually involves inspecting things such as ethernet cabling pinouts or NICs on a PC.

Real life scenario: "I have plugged an ethernet cable into my PoE switch but can't see a power light"

Best Guess

The best guess method relies on your knowledge of TCP/IP protocols. If your issue exhibits characteristics of a particular OSI layer, start the troubleshooting there. This method can often be used in conjunction with the top-down or bottom-up approach.

Real life scenario: "My device log in to a network switch. I will start at layer 3 and check that IP addresses are configured correctly"

Conclusion

Whilst this not an exhaustive list of troubleshooting techniques, it is a good place to start.

One other bit of advice would be to form your issue into a question and Google, you would be surprised how often someone has experienced the same issue.