Red Hat Bugzilla – Bug 126678
poor net performance to certain sites
Last modified: 2007-11-30 17:10:45 EST
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User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7)
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
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):
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?