DNS, or MTU problem? A simple test.

Often times, our computers may seem as though 'something is wrong'. It may be that a page is not loading, or it seems 'slow'. This may, or may not, indicate a network problem, either a DNS (Domain Name System) or an MTU (Maximum Transmission Unit) problem, but a simple testing procedure, you can do in 10 minutes - yourself, may save you some worry, and find out, for sure. Let's pretend your photos/images are the problem ...

So, how to do that?

Firstly, the thing I would do, if testing for these problems, is clear my Browser's Cache. For example -

Firefox...V2.0.0.16

Go to Tools, Options, Privacy, Private Data - check that 'cache' is selected (only), click OK. (You can also pre-set cache in the "Settings").




Internet Explorer 7, - Tools, Internet Options, General Tab, Browsing History, Delete, Select Temporary Internet Files, Click OK. This is also the screen option for deleting Cookies/Browsing History.
Be careful not to delete what you don't want to!





Secondly, I need to create a 'baseline' of performance. This requires me to 'clean the slate', so to speak.
To do that, I need to 'flush' the DNS.

Open, or 'run', a 'Command Window', (click on 'Start' , then 'run') - typing the request- ipconfig/flushdns




...type, cmd



... type, ipconfig/flushdns where the cursor is flashing, and '<enter>'.



... you will get a message, as in the next image: "Successfully flushed the DNS Resolver Cache"



Now I am ready to perform my 'baseline' checks. What I need to do, each time I notice this problem, is a simple 'four-part test'.

'Run' a 'cmd' window, N.B. (You need to have it copied to Notepad), so ...

• Type - ipconfig /all >c:\ipconfig.txt - into a command window... <enter>
  
• Then, type - notepad c:\ipconfig.txt - into the same command window, for immediate examination of the information... <enter>
  
  

Now, I need to 'ping' my IP address to establish a 'baseline'. Type into the 'cmd' window ping XXX.XXX. XXX.XXX (this being your IP Address), and <enter>. Please, take special note of the 'settings' as indicated in the following image ... (this is NOT my actual IP, but your IP will be similar).



Next, you need to 'ping' something to test against your 'baseline'. So, to make it easy, from the Command Window, type, ping www.yahoo.com - This will give you a result - and - the IP Address for www.yahoo.com

Note success / exact text of error messages - Packets sent, Packets received, Packets lost plus times etc.




Then, from your Browser, type separately, and Browse both, the...

• IP Address - (of www.yahoo.com) and the...
• URL... www.yahoo.com

Note: success and, also, note any 'differences' in the way the screen displays , or time it takes to open etc, between the browsed IP address and the Browsed URL.


Now, do exactly the same, again - for photos1.blogger.com - (IP and URL Address).Once you have done both tests... if you see a difference between both IP address accesses, as compared to both URL accesses, you very likely have a DNS problem. If you can 'ping' (with a successful return), but not 'browse', with identical results for IP address and URL, you may very well have an MTU problem.

If you see a combination of results, you may need to research both a DNS and an MTU problem.


Okay, what did all that prove?

• It proved whether your Computer has a Server connection which is losing packets during transmission.
• It proved whether you may, or may not, have a DNS problem.
• It proved whether your computer may, or may not, have an Transmissions Unit (MTU) problem.
• It proved whether you need to look elsewhere for the problem.

Let's say everything is OK. That leaves Blogger. Now, lost packets of transmission are expected. 100% transmission is an unreal expectation. It's called the 'Lossy' principle. It is where a certain amount of loss is expected, without greatly affecting the end result and without effecting a loss. For example, a photocopy gets bigger the more you copy it, but you can still see it virtually intact. A photo will lose quality, and show some distortion the more you compress it, but will stay reasonably recognisable to the eye. Some loss is expected.

(see also: DNS and MTU - Interpreting Results)

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