DNS and MTU - Interpreting Results

In August, I re-hashed an old post on a Simple Test for detecting either a Domain Naming Service - DNS, or Maximum Transmission Units - MTU problem.

The test itself, is not a remedy. It is a simple diagnostic tool. Running this test, will assist you to find out in which area you should be looking for an answer - or further testing/information. I always consult PChuck's Network, when I have a problem. I follow his advice. If he says do a test, I do it. Then I get answers which we can discuss further, and develop our strategy for a 'fix'. So, testing is the first step.

The test described above, will tell me ...

• If I have connectivity problems and need to look elsewhere
• If I can eliminate connectivity
• If I need to adjust anything, like an MTU setting

For instance, interpreting the results ...

1. Send 4 packets, Rec'd 4 packets = Success: You have basic connectivity with the server.
   
2. Send 4 packets, Rec'd 0 packets = Fail: You have no connectivity with the server. You have to look for a connectivity problem - (You may want to use Pathping, or Pingplotter, to find out where you're losing connectivity)
3. Host Unknown = Fail: Your DNS is not providing an address for the server (continue troubleshooting)

Now, as also mentioned in my other post, consider the results of the tests... (see also: PChuck's Post)
(This is an excerpt from Chuck's post)

• Conduct a '4-step' test.
  
  • From a command window:
    1. Ping www.yahoo.com.
    2. Ping 209.131.36.158.
    3. Note success / exact text of error messages.
  • From your browser:
    1. Browse www.yahoo.com.
    2. Browse 209.131.36.158.
    3. Note success / exact text of error messages.
• If you see Success for both the browse and ping by IP address, and Fail by the browse and ping by name, you very likely have a DNS problem.
• If you see Success for ping but not for browse, identically for IP address and name, you may well have an MTU setting problem.
• If you see a combination of results, you may need to research BOTH a DNS and MTU problem.
• If the tests aren't conclusive, consider the ubiquitous LSP / Winsock corruption problem. If your computer runs the latest Microsoft operating system, aka Windows Vista, consider several possible more exotic problems.

OK. So, now you have your test results, you will know which area you need to look at, or, if not, you need to do more testing. Either way, it will be easier when you have eliminated some of the reasons.


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