Red Hat Bugzilla – Bug 126678
poor net performance to certain sites
Last modified: 2007-11-30 17:10:45 EST
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040619 Firefox/0.9 Description of problem: If I browse to www.dell.com everything works fine. If I then click on the Small Business link and browse to http://www1.us.dell.com/content/default.aspx?c=us&cs=04&l=en&s=bsd net performace goes to zero. Another site with zero performance is www.zmaxtech.com. Many others like slashdot, yahoo, linuxtoday work fine. Backing off to kernel-smp-2.6.6-1.435 fixes everthing. Both the Linus vanilla and Redhat kernels have this problem. I captured packets to the site and don't see anything wrong. At the problem sites one TCP packet is transmitted every half second or so. No obvious protocol errors. Boot Windows or a 2.6.6 kernel and the site works fine. I don't think it is the e1000 driver since some sites work fine and others don't on a 2.6.7 kernel which show this problem. pings work fine to the problem sites. Version-Release number of selected component (if applicable): kernel-smp-2.6.7 How reproducible: Always
It's a bug in Cisco routers when NAT is enabled. It corrupts TCP SACK blocks in packets, which causes lots of problems for the connection. It happens when a non-zero window scale is used for the TCP connection, which is what the newer Linux kernels are doing by default. It's not a Linux bug, and Cisco needs to own up to this problem and provide a fix for their customers.
Is there a simple work around while we wait on Cisco?