[isp-caching] Re: Fwd: How to check a web site is cached or not?

[Alex Rousskov <rousskov@...>]

On Fri, 26 Mar 2004, Shawn Xu wrote:

> Thank you for your suggestion, but I am attempting to use the cache
> server as transparent mode. Therefore, only one interface is used on
> the cache server. On our L4 switch I configured to redirect http to
> the cache server. So I don't know how to run something like tcpdump
> on it.

I guess the simplest, albeit not the most precise, test would be to
disconnect/down the outgoing link to the Internet just before
re-requesting the page in question. This assumes the IP of the page
domain got cached by the browser or its OS. Or you can use an IP for
both the first and the second request. Or prohibit all traffic from
the cache to the Internet and do not worry about DNS.

Checking cache logs is even simpler, provided you agree with the
vendor definition of a hit.

Finally, you can check response headers for Age value. This again
relies on you agreeing with vendor way to calculate age (and on vendor
being compliant enough to add Age header to responses). Some caches
add extension headers indicating HIT/MISS status. You can see HTTP
response headers in tcpdump or just use wget with an appropriate
command line option.

Alex.







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