How web proxy server works in terms of Caching..Confusing me

[ift38375]

Hi Experts,

I have used many proxies server like Winproxy, websense, ccproxy
but Did not know about caching until today,I just used proxy
server as a Web filtering only. I want to know about how caching works
in proxy server and How can user retrieve webpages offline if internet
goes down. how can i check it practically in my LAN.

suppose Three days ago I opened a website cisco.com
(http://www.cisco.com/router/vpn/security.html)

Suppose that today my internet goes down then how to see same given
above URL (http://www.cisco.com/router/vpn/security.html) page through
Proxy cache.There are possible cases where i am confuse :

1. How to browse or access above link, mean to say
what i need to type in browser, www.cisco.com only
or http://www.cisco.com/router/vpn/security.html ?

2. In case1, i taken only one specific URL like
"http://www.cisco.com/router/vpn/security.html"
but It is not necessary that three days ago I
have just browsed only one page,Obviously lots
of pages will be opened like as
"http://www.cisco.com/router/ips/dos.html"
"http://www.cisco.com/switch/vlan/native.html"
"http://www.cisco.com/voip/h323/protocol.html"
"http://www.microsoft.com/server/license/perseat.aspx"

then what should i do, is there any need to remember all
these link or note down or bookmark. i think so it is not
possible,How can i reach to desired page ?


3. Last question is related to monitoring purpose, My question
is how can i check cache webpages or data that Whether it
exists or not?

KS

[adrien]

Hi

when a web server sends a page or image or other web resource back to a browser (or proxy), it may include a Cache-Control field which specifies how the resource is to be treated for caching.

Some sites specify that their content must not be cached, or can be re-used without revalidation for a period of time.

WinGate honours these Cache-Control instructions.

So, whether or not a page is in WinGate's cache, will depend on the response it got and what it was told to do.

We're currently re-writing the WinGate cache module for 2 reasons:

1. SQL-based indexing is too slow for even medium sites without significant investment in database infrastructure which we feel is too much
2. Heuristic caching. We wish to increase the utility of the cache, but if only Cache-Control or Expires header is used to control cachability, then we find not enough of the internet specifies useful cache controls. Therefore we need to introduce a level of caching without any instruction from the server. This is the thing that should be more interesting to you, as it will allow you to override server response cache control directives, and force storage of resources. There are caveats with this however, as it can prevent some sites from working properly.

So in the meantime, there's not much you can do. You can use WinGate policy to force new Cache-Control headers into responses before they are seen by the cache (e.g. edit Cache-Control header in responses in the ProxyResponse event). This can trick the cache into storing the page. If you set a max-age directive you can make the page available even when the server is unreachable.

HTTP caching is a fairly large and complex area, if you want the ultimate reference, it's at the IETF, http://tools.ietf.org/html/draft-ietf-h ... 6-cache-21

Regards

Adrien de Croy