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Date: Tue, 2 May 2000 23:23:55 -0700
From: Jan Koum <jkb@ethereal.net>
To: Jeff Gallagher <jeffg@cs.mun.ca>
Cc: freebsd-net@FreeBSD.ORG
Subject: Re: Help with tweaking the stack and connections in 4.0
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In-Reply-To: <017701bfb490$2684f040$47b02fce@ntc.nf.ca>; from jeffg@cs.mun.ca on Tue, May 02, 2000 at 09:12:59PM -0230
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On Tue, May 02, 2000 at 09:12:59PM -0230, Jeff Gallagher <jeffg@cs.mun.ca> wrote:
> I need a little help here with some aspects of FreeBSD (and perhaps Unix)
> that I am not real familiar with.


if you are not familiar with it, you shouldn't mess with it ;)


> I need to change the default TCP window size from 16384 to various other
> numbers. (Not on the fly of course)
> What files do I have to change and what do I have to (re)build to make such
> a change take effect?

[i never tried this sysctl change before, so i am not 100% sure it works]

$ sysctl net.inet.tcp.sendspace
$ sysctl -w net.inet.tcp.recvspace=XYZ


> I also need to increase the total number of simulatanious connections. (Open
> connections) I am trying to test some networking software and I need to
> flood the connections on the remote box and right now my FBSD box is dying
> first - says something like jess: buffer overflow.  (Humm, isn't there a DoS
> attack that does this?) Again what file(s) do I need to modify and (re)build
> to make such a change.


i bet the message you are getting is: Out of mbuf clusters - increase maxusers!

so do what it is asking you to do: increase maxusers in your kernel.
see handbook on how to build and install a custom kernel


> Is there a specific group of files that control the networking portion of
> the OS that will allow me to tweak some of the other details of the stack?


yes. look in /usr/src/sys/netinet -- what exactly do you want to change
and why?


> Does anyone off hand have any quantative data on the speed of the TCP stack
> in FreeBSD. (Url link maybe?)


not of hand. but it is one of the best around. i would like to see an url
however which talks about where freebsd is lacking right now compared to
other modern OSes.


> Sorry for the perhaps silly questions, but I am not well versed in the
> layout and distribution of the FreeBSD sources. I checked LINT to see if
> some of these were "obvious" kernel options but the only thing close was the
> ICMP bandwith limiting.


if you are on recent freebsd box, type "man loader" and look at the bottom
of the "BUILTIN ENVIRONMENT VARIABLES" section there.

wanna tell us what exactly are you trying to do here and why?

-- yan


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