Subject: Re: TCP/IP tuning
To: Thomas Miller <>
From: Jean-Edouard BABIN <>
List: current-users
Date: 02/28/2004 05:08:55

I think that for a 5Mb/sec connection you did not have to tune the system t=
much (exept if you use a very old computer...)
Tuning may be more usefull for Gigabit i think
Also on my kernel (1.6ZH) kern.mbuf.nmbclusters can be changed with sysctl

on 28/02/04 4:16, =AB=A0Thomas Miller=A0=BB <> wrote:

> Hello,=20
> I have a new cable connection which is supposed
> to give me downloads of "up to 5 Mb/sec," and I
> want to tune my -current i386 1.6ZK system to
> take advantage of the new connection.
> I found the following:
> 1. Enabling High Performance Data Transfers
> 2. TCP tuning cookbook
> and the the latter gives specific suggestions
> concerning NetBSD-current:
>  Only  NetBSD-current  (upcoming  version  2.0) seems to support really
>  fast  connections, as there has been much work done on the "zero-copy"
>  TCP features of NetBSD lately.
>    * Install NetBSD-current
>    * Increase  IFQ_MAXLEN in /usr/src/sys/net/if.h from 50 (default) to
>      something like 1000
>    * Enter  the  line "options NMBCLUSTERS=3D16384" in Your kernel config
>      file
>    * Recompile  and  install  Your  new  kernel.  Do not try to set the
>      values  below too high until You have increased NMBCLUSTERS - risk
>      of "hanging" the network part of the OS!
>  Command
>  Description
>  sysctl -w net.inet.tcp.rfc1323=3D1 Activate window scaling and timestamp
>  options according to RFC 1323.
>  sysctl -w kern.sbmax=3D[wmax] Set maximum size of TCP window.
>  sysctl  -w  net.inet.tcp.recvspace=3D[wstd]  Set  default  size  of  TCP
>  receive window.
>  sysctl  -w  net.inet.tcp.sendspace=3D[wstd]  Set  default  size  of  TCP
>  transmit window.
>  sysctl  kern.mbuf.nmbclusters  View  maximum  number of mbuf clusters.
>  Used  for  storage  of data packets to/from the network interface. Can
>  only be set by recompiling Your kernel - see above!
> I was unable to find much about TCP/IP tuning in
> the web pages or in the mailing list
> archives.  So, before I wade in and start changing
> stuff, I though I'd ask here if the above information
> seems correct and complete.  Any additional hints
> or tips would be appreciated.
> Thanks! =20
> Tom

Jean-Edouard BABIN
Web :
IRC : Jeb @ Undernet