Neohapsis is currently accepting applications for employment. For more information, please visit our website www.neohapsis.com or email firstname.lastname@example.org
From: Viktor Dukhovni (postfix-usersdukhovni.org)
Date: Tue May 07 2013 - 12:26:36 CDT
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:
On which operating systems does this suppress window scaling during
the TCP 3-way handshake?
I tried MacOSX and NetBSD, neither seemed to suppress window scaling
when the server window size was set to 32767:
C > S: Flags [S], seq 227891400, win 65535, options
[mss 1460,wscale 4,TS val 342104207 ecr 0,sackOK,eol], length 0
S > C: Flags [S.], seq 3628790798, ack 227891401, win 32767, options
[mss 1460,wscale 3,TS val 1 ecr 342104207,sackOK], length 0
Have not tried Linux yet, perhaps this works there...