Re: 2.6.7-mm1 - 2.6.7-mm4 weird http behavior

[John Heffner]

On Tue, 29 Jun 2004, Stephen Hemminger wrote:

> On Tue, 29 Jun 2004 13:59:22 -0700
> "David S. Miller" <davem@xxxxxxxxxx> wrote:
>
> > On Tue, 29 Jun 2004 13:35:01 -0700
> > Stephen Hemminger <shemminger@xxxxxxxx> wrote:
> >
> > > FYI - gentoo works for window scale 0..2 and appears to fail for >3.
> > >
> > > Also, the socket ends up with:
> > >
> > > State      Recv-Q Send-Q      Local Address:Port          Peer Address:Port
> > > ESTAB      0      0             172.20.1.73:34452       198.63.211.232:http
> > >          ts sack wscale:0,3 rto:332 rtt:66.375/50.5 cwnd:3
> >
> > Yes, I've seen this declared in other reports too.
> >
> > It probably means just that for window scales of 0..2 the misinterpretation
> > does not result in a too-small-to-send-data window.
> >
> > But I'm still confused that the scaled window is being given to the
> > receiver, and this makes the connection freeze.  I wonder if there is
> > a queer box doing NAT or similar in front of the gentoo machine which
> > either:
> >
> > 1) Applies any window scaling to both directions
> > 2) Applies window scaling to the wrong direction
> >
> > and uses this to "help" with dropping of out-of-window TCP segments.
>
> Unfortunately, this means the default probably means that window scale must be
> disabled. An interesting experiment would be to see if other implementations have
> the same problem with window scale enabled.


Sigh.  I ran in to this problem a year or so ago and it was a broken
firewall that was mangling the TCP window scale option.  I think the
firewall was an OpenBSD machine, and I was told the problem went away with
an upgrade.  I'm curious what they're running here.

The boundary 3 is special because it causes SWS avoidance to break.

  -John

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