A Procedural Methodology for Diagnosing (Home) Internet Issues

This post was published 10 years, 6 months ago. Due to the rapidly evolving world of technology, some concepts may no longer be applicable.

Step 5: Modem

There are typically some statistics available through the modem. These tend to be quite helpful in certain aspects of diagnostics, and should be noted.

Login to your modem (if connected directly, the address tends to be Things to note include:

  • Modem make/model/firmware
    • This is just general information, that could be useful for finding out more about your modem
  • Upstream/Downstream rates
    • This is the line rate – what data rate is currently enabled on the line (profile)
  • Upstream/Downstream margins
    • This refers to the signal to noise ratio margins – higher numbers are better, values of 6dB or below typically will not work, 20dB or higher is ideal.
  • Upstream/Downstream line attenuation
    • This refers to the loss of signal strength, generally correlated to line length – lower is better, values of 60dB or lower is typically necessary; 30dB or lower is ideal

One additional thing would be to attempt lowering the size of the MTU. The maximum size is usually 1492 bytes. Reducing this value might improve stability (but typically reduces performance – of course, that isn’t an issue if things are working).

Restart your modem – restarting components tends to fix a lot of problems.

If possible, attempt to switch your modem for another that you know works. This will help to eliminate the modem as a possible problem.

It does help to check that the modem’s internet LED is on and that components are plugged in and powered up.

Step 6: Phone line/cable

This section refers more to DSL, but might have some point applicable to cable internet. On DSL, line interference is a significant issue. It is typically addressed through the use of DSL filters. Ensure that EVERY device connected to your phone line (except your modem) has a DSL filter on it.

It really isn’t a bad idea to at least see that your phone works if you are using DSL.

Additionally, the contacts at every jack should be inspected. If there is corrosion on the line, it can greatly reduce signal quality, even if it isn’t on the jack your modem is plugged into. To do this, open the faceplate of each phone jack (so that you can see the wires), and check for corrosion (typically green or black on the copper wires).

Just to be thorough, I would suggest unplugging every other telecommunication device from the phone jacks and seeing if the Internet connection improves (each device adds some interference, and it is possible for a single faulty device to affect all the others). Additionally, try to plug the modem into different jacks and see if there is any change. If possible, try to connect your modem directly to the demarcation point, as this will essentially eliminate any problems with your internal wiring.

Step 7: Your ISP

By now, you can be fairly confident that you have eliminated every component in your house that could be causing the problem, the problem likely falls into the realm of your ISP or phone/cable company. Give them a call, and hope for the best (usually, they do have some decent diagnostic tools that can identify a problem remotely, but unfortunately, they don’t always come to the right conclusion).

Step 8: The Internet

When you eliminate all other possibilities, the one that remains, however, unlikely, must be true – while perhaps not verbatim, it is an oft quoted line from Sherlock Holmes. If there really isn’t anything wrong with anything – then it is possible that a part of the Internet is actually down. While this is extremely rare, there have been times when Internet backbones have failed, or when natural disasters have cut off traffic to significant sections of the Internet, these do not, however, typically last for extended periods of time (in other words, if things aren’t back to normal by the time you make it through all the above sections, and no one else you know has a problem, the Internet probably is working just fine).

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