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

It can be cached. But Squid malfunctions with it in major ways, especially due to
very serious blunders (I don't know else to put it; that's what they are) in its
handling of partial content. Having a Squid cache with Windows clients behind
it can literally destroy the usability of your network.

--Brett Glass

At 03:31 AM 4/19/2005, Joel Jaeggli wrote:
  
>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client makes its next request, Squid queries the Windows update server and is told that its current copy of the file is out of date.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 y
ou'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
>
>--
>-------------------------------------------------------------------------- Joel Jaeggli Unix Consulting joelja@darkwing.uoregon.edu GPG Key Fingerprint: 5C6E 0104 BAF0 40B0 5BD3 C38B F000 35AB B67F 56B2
Received on Tue Apr 19 2005 - 11:37:41 MDT