Viktor Dukhovni:
> On Tue, May 07, 2013 at 12:57:27PM -0400, Wietse Venema wrote:
>
> > Viktor Dukhovni:
> > > That said, clearly some packets from the sender are lost, and never
> > > retransmitted. The TCP connection negotiates selective ACK and
> > > window scaling on both sides. First thing I would do is disable
> > > window scaling on your Postfix server. This will reduce throughput
> > > for mail from far away senders (without window scaling Hong Kong
> > > to USA will be at most 64KB per ~0.25 sec or 4 sec per MB of data).
> >
> > Postfix 2.6 and later have a workaround for TCP window scaling bugs.
> > For detailed instructions, see:
> > http://www.postfix.org/postconf.5.html#tcp_windowsize
>
> On which operating systems does this suppress window scaling during
> the TCP 3-way handshake?
It's five years since this I added the tcp_windowsize feature, and
the systems that I was using at the time have been decomissioned.
Even with minuscule window sizes I see a non-zero wscale option in
the SYN+ACK response from FreeBSD 8. I'll update the documentation.
Wietse
