Re: [squid-users] Major malfunction: Squid and Windows Update

microsoft update makes a pretty serious effort to be uncacheable.

On Mon, 18 Apr 2005, Brett Glass wrote:

> After this month's "Black Tuesday" (the Tuesday on which Microsoft released a
> large number of bug fixes and patches and also eliminated the pacing of
> Windows XP Service Pack 2 downloads), our Squid caches went berserk, drawing
> massive amounts of data from the Net and clogging our ISP's downstream feeds.
> Upon inspection, we saw what went wrong. Windows Update downloads updates by
> requesting portions of files -- as little as 300 and as much as several
> thousand bytes -- via HTTP. Unfortunately, when a Squid proxy is between the
> Windows Update client and the Internet, this wreaks havoc. When the first
> request occurs, the Squid proxy downloads the entire file before providing
> the subrange of bytes to the client (perhaps making the reasonable assumption
> that it will ask for other portions later). But when the client makes its
> next request, Squid queries the Windows update server and is told that its
> current copy of the file is out of date. So, it transfers the entire file
> AGAIN. (If you're interested, I can send tcpdump output showing this. It has
> clients' addresses, so I probably shouldn't post it publicly.) The smaller
> the chunks requested by the client, the larger the wasted bandwidth.
>
> It seems to make no difference if one sets "reload-into-ims" or even
> "ignore-reload" and "override-expire" and "override-lastmod" for Windows
> Update downloads. That's right: you can set
>
> refresh_pattern download\.microsoft\.com 144000 100% 144000 ignore-reload
> override-expire override-lastmod
>
> and Squid still reports misses on successive accesses to the same URL.
>
> Can this problem be diagnosed and fixed? It's causing such a massive waste of
> bandwidth that we're looking at dumping Squid.
>
> --Brett Glass
>

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Joel Jaeggli  	       Unix Consulting 	       joelja@darkwing.uoregon.edu 
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