Fedora Core 5 x86_64: some network connections fail

[Matt Morgan]

On 8/25/06, Jay Cliburn <jacliburn at bellsouth.net> wrote:
> Matt Morgan wrote:
> > I'm having a new (to me), strange networking problem on an FC5 install
> > on a new computer. Basically, I can't make some network connections to
> > some sites. The best way to explain this is probably with some
> > examples:
> >
> > 1) I can ssh to my own server.
> > 2) I can http to my own server, but I can't download the image on my
> > home page (a very small png). Nor can I get the squirrelmail home page
> > to load from that server.
> > 3) I can login via IMAP to my own server, but then Thunderbird times
> > out when downloading mail.
> > 4) I can login via POP3 to my ISP email account, but then Thunderbird
> > times out when downloading mail.
> > 5) I can get to any google web site, like my gmail, and to
> > register.co.uk via http, but I can't download slashdot pages or New
> > York Times pages or most other web pages (timeout on "Waiting for
> > /server/").
> >
> > In all the cases of failure, it's not DNS--I get the address fine.
> >
> > On the same computer I have a Windows XP install, where all these
> > things work fine. So I know it's not hardware. For what it's worth,
> > everything worked fine for a about a day and a half before I lost some
> > networking. I'm clueless as to what might have changed since it
> > worked.
> >
> > The network adapter is an SiS 190, which is historically problematic
> > in Linux, but I thought it was all supposed to be worked out in FC5.
> > System-config-network calls it a "Silicon Integrated Systems [SiS]
> > Unknown Device 0190," though, which doesn't sound good.
> >
> > I have seen links to an SiS-provided driver for the 190 that I can
> > compile and install (eg
> > http://www.cse.iitb.ac.in/~mohitz/tech/lan.php) but they look old
> > (kernel 2.6.9 era). Is there some easier/more current way to get it
> > working on FC5? I checked this list for help, and I don't see any
> > complaints about this adapter since FC3 ...
> >
> > Thanks,
> > Matt
> >
>
> You didn't specify what kernel you're using, but these symptoms sound
> like a TCP window scaling issue.  TCP window scaling was changed in
> 2.6.17, and certain middleboxes in the network pathway to your
> destination sites might not be able to handle it.  FreeBSD systems are
> also susceptible.  Google for details.
>
> Become root and issue this command, then retry your connections.
>
> sysctl -w net.ipv4.tcp_window_scaling = 0
>

That sounds extremely likely ... I bet what happened was that it
worked fine on the install (from CDs) and then I updated the kernel
right away, but didn't reboot for a day or two. So when 2.6.17 kicked
in ...

I can't check it until tonight, but I bet you nailed it. Thanks.