Lagado Tools  

Cache Test

The Lagado Cache Test will help expose stealthed transparent proxy caches. Stealthed transparent proxy caches are those which do not announce themselves to the origin web server and can appear to behave like a normal client. They may even masquerade as a client to make their requests.

Use this test when the regular Lagado Proxy Test shows no proxy but you feel there might be one there anyway.

This test is very simple but requires a little work from you.

page serial number303063
page generation time
page age

Note: page generation time and page age are valid only when your workstation clock is set for accurate time.

Please follow the steps below.

Step 1

Note the page serial number somewhere.

Step 2

Clear your browser's cache

For Internet Explorer (Windows)
Tools > Delete Browsing History... > Make sure everything except "Preserve Favorites website data" and "Temporary Internet files" is unchecked > Delete
For Firefox (Windows)
Tools > Options > Advanced > Network > Clear Now (under Offline Storage)
Tools > Clear Private Data... > Make sure everything except "Cache" is unchecked > Clear Private Data Now
For Safari (Windows)
General Safari settings menu (the gear and down-arrow on the right side of toolbar) > Reset Safari... > Make sure everything except "Empty the cache" is unchecked > Reset
For Firefox (Linux)
Edit > Preferences > Advanced > Cache > Clear Now
Tools > Clear Recent History... > Make sure everything except "Cache" is unchecked > Clear Now
For Opera (Linux)
Menu > Settings > Delete Private Data... > Detailed Options > Make sure everything except "Delete entire cache" is unchecked > Delete

Step 3

Click on this link to load this page again. (Alternatively, you may browse to this page or use a bookmark. Do not hit refresh.)

If the page serial number is the same as when you noted it at step 1 you are most likely using a caching proxy; stop here - Proxy Found.

If the page serial number has changed you may not be using a caching proxy. To be more certain check the page age.

The page age shown is only valid when your workstation is set for accurate time (a few seconds error won't matter). If you adjust the time start again at step 1.

If the page age is no more than a few seconds there is no evidence of caching occuring so a proxy is not evident; stop here - No Proxy Found

If the page age is more than 30 seconds you may have picked up a fresher version of this page loaded into a proxy cache by someone else. It may be worth repeating the test to see if you get a more conclusive result.


Background Discussion

This test makes unique pages that behave as static pages. Caches operate on static pages because they can usually rely on them staying valid for a period of time.

These pages set a last modified date of three days before they are generated. They also set an expiry time of three days days into the future. This should encourage most caches to serve future requests for this page from the cache unless explicitly bypassed with the browser refresh button.

The tricky part of this test is to make sure that you are not just getting the page from the browser's local cache. Notice how each time you visit the cache-test (without hitting refresh or clearing the browser's cache) it gives you the same version which it is getting from the browser's cache.

This test will only expose caching proxies. It will not expose proxies that have some other goal or those that are selective about which sites they cache.


Selected Response Headers For This Page

The Lagado server added the following headers to the response to affect the behaviour of caches.

Last-Modified: Wed, 16 Apr 2014 19:32:47 GMT
Expires: Tue, 22 Apr 2014 19:32:47 GMT
Cache-Control: max-age=259200
Date: Sat, 19 Apr 2014 19:32:47 GMT

Updated 17 Sep 2010: Revised cache clearing instructions - thanks Keith