Red Hat Bugzilla – Bug 253680
Shortcomings in network configuration
Last modified: 2007-11-30 17:12:13 EST
Description of problem: Fedora 7 doesn't take a lowest-common-denominator approach to networking and seems to presumes that the networking equipment being used is capable of supporting networking features like tcp window scaling. This is probably a reasonable assumption, but unfortunately a lot of off-the-shelf networking hardware is broken with respect to some advanced features of networking like tcp window scaling, which can result in dreadful networking slowness and problems when used with linux, and at a complexity way beyond what your average user will be able to diagnose or investigate following linux installation. In my case, adding net.ipv4.tcp_window_scaling=0 to /etc/sysctl.conf solved the weird networking problems evident but it took some hours to figure out what the problem was and I'm a programmer. Yes there are problems with router devices that need fixing, but in the circumstances of there being a lot of devices out there that are broken in some respect, I believe that it is a shortcoming of the installation procedure that it doesn't detect networking incompatibilities such as this and report any incompatibility to the installer, offering installation of a workaround as I've mentioned above. Another question arises however for mobile computing users and that is...how can these type of issues be dealt with when connecting to arbitrary networks? Version-Release number of selected component (if applicable): as in 2.6.22.1-41.fc7 How reproducible: always in my circumstance Steps to Reproduce: 1. Install linux from DVD 2. Observe lousy network behaviour and latency when connected to router that apparently doesn't support tcp window scaling (Draytek 2900VG in my case) Actual results: Lousy network performance Expected results: Reasonable network performance Additional info:
This article contains some quite interesting information about tcp window scaling.... http://lwn.net/Articles/92727/
Sorry, we can't really mess with this because the simple fix would severely limit performance for people whose networking hardware works properly, and we can't implement a more complex one because we'd have to maintain that across kernel releases.
GRR someone reaassigned this to kernel and I did not raise this against kernel... it isn't a kernel issue - my point being that either the installer or the network scripts should have some smarts to detect network problems