On Sat, Oct 11, 2008 at 02:31:12PM -0400, Sahil Tandon wrote:
> > Your server offers Window scaling (WS=3). Either the client's firewall or
> > yours is confused by window scaling. You may need to turn window scaling
> > off (it is a pity that many "new" TCP features are unusable in practice
> > due to firewall breakage).
>
> That was it. After setting net.inet.tcp.rfc1323=0, mail is delivered to
> user's mailbox in less than 2 minutes after the initial connect. I'll
> take this to a more appropriate forum now, but want to understand
> whether disabling window scaling will adversely impact the
> system/postfix's performance.
Servers on long-haul (satellite link or half-way around the world) high
bandwidth networks will not be able to utilize the full bandwidth of the
connection. With a 32kB maximum window size (implementations tend to not
use window sizes with the high bit set to 1) and a round-trip latency of
400ms, you can sink at most 32 * 8 * 2.5 = 640 kbps. If the client limits
destination concurrency to 20, it can send at most ~12 Mbps to the server.
In most environments this is sufficient, but if you want to fill an
expensive long-haul leased line, this could be a problem.
> I tested sending much larger files from
> other servers and there is no problem even when scaling is enabled, so it
> appears the sending server is the one confused by scaling.
Almost never the server itself, rather the firewall between the server
and the Internet.
--
Viktor.
Disclaimer: off-list followups get on-list replies or get ignored.
Please do not ignore the "Reply-To" header.
To unsubscribe from the postfix-users list, visit
http://www.postfix.org/lists.html or click the link below:
<mailto:[EMAIL PROTECTED]>
If my response solves your problem, the best way to thank me is to not
send an "it worked, thanks" follow-up. If you must respond, please put
"It worked, thanks" in the "Subject" so I can delete these quickly.
