Hey all, In working on a computer for myself I stumbled across an issue that may affect our student machines. I was working on installing Debian Etch AMD64 on a new SATA drive. What I discovered was this:
Any computer running Debian Etch on my home network, was having odd problems connecting to certain sites on the Internet. Some sites, like Google (and our BWorks home page) were just fine. Some other sites, worryingly including the security updates at security.debian.org, would not reply. Browser would just sit and spin, or if I was running apt-get update/upgrade, it would freeze up once trying to connect to the Debian servers. Ubuntu machines, just fine; likewise the same machine running Debian Sarge. But put Etch in the same machine, and WHAM! Same problem. Turns out it isn't as much a bug as a feature, so they say, or in this case, a broken server somewhere. The problem, it turns out, is in kernels higher than 2.6.16 (which is what my Ubuntu 6.06 is; Sarge is something like 2.6.8), and Etch is using 2.6.18. The release notes for Debian Etch Intel x86 point out, in their issues to be aware of: 5.1.3 Certain network sites cannot be reached by TCP Since 2.6.17, Linux aggressively uses TCP window scaling which is specified in RFC 1323. Some servers have a broken behavior, and announce wrong window sizes for themselves. For more details, please see the bug reports #381262, #395066, #401435. There are usually two workarounds to these problems: either revert the maximum allowed TCP window sizes to a smaller value (preferable) or turn off TCP window scaling altogether (deprecated). See the example commands in the debian-installer errata page. ====== Here are the URLs of sites that had useful information: http://articles.techrepublic.com.com/5100-1035-6174075.html http://kerneltrap.org/node/6723 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=401435 http://www.debian.org/devel/debian-installer/errata http://www.debian.org/releases/stable/i386/release-notes/ch-information.en.html We need to test the student installs, and if needed apply one or more of the "fixes" (most likely turning off TCP window scaling permanently) to the machines before we send them out. The problem may be as simple as my own firewall or router, but I seem to recall trying to run an apt-get update/upgrade at the shop and seeing the same freeze-up behavior. I think we should do some testing and find out, in any case. t. -- *** Propositions arrived at purely by logical means are completely empty as regards reality. - Albert Einstein ***
