North American Network Operators Group

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Re: Adjusting TCP windows on production systems?

  • From: Petri Helenius
  • Date: Wed Oct 01 03:27:35 2003

Steve Francis wrote:

Just as a head up - this sort of below should not be done on things like web servers that support lots of concurrent connections - you'll eat all your memory for sockets.

Unless you have something like FreeBSDīs auto-tuning inflight window stuff which
would allow large windows to be allocated only when the delay*bandwidth product
justifies it.


Marshall Eubanks wrote:

On Tue, 30 Sep 2003 15:44:03 -0400
"Temkin, David" <[email protected]> wrote:

Is there anyone in a production environment who, as part of their system
build process, adjusts the TCP receive window/MSS/etc. on production

As a concrete data point:
the tuning below on Solaris 9 increased the TCP data transfer rates from
SJC to NYC by a factor of 10:
(i.e. from 2 to about 20Mbps with ftp; 1 to 11Mbps with scp.)

ndd -set /dev/tcp tcp_recv_hiwat 400000
ndd -set /dev/tcp tcp_xmit_hiwat 400000
ndd -set /dev/tcp tcp_wscale_always 1
ndd -set /dev/tcp tcp_max_buf 10485760