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current copy of the file is out of date.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 [EMAIL PROTECTED] GPG Key >Fingerprint: 5C6E 0104 BAF0 40B0 5BD3 C38B F000 35AB B67F 56B2
