From owner-freebsd-net  Sun May  3 17:09:23 1998
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To: Pierre Beyssac <pb@fasterix.freenix.org>
cc: freebsd-net@FreeBSD.ORG
Subject: Re: patches for fast forwarding (with kernel option & sysctl) 
In-reply-to: Your message of "Mon, 04 May 1998 01:43:10 +0200."
             <19980504014310.A22037@fasterix.frmug.fr.net> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Sun, 03 May 1998 17:07:30 -0700
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X-Loop: FreeBSD.org

Here are new patches to use NetBSD's IPFLOW stuff on -current. To
use, store ipflow.c in /sys/netinet, then add IPFLOW to your kernel
config. After booting, activate with:

   These appear to contain the broken header checksumming code. That'll need
to be fixed before these are integrated. There is a NetBSD #5380 open on 
this - author Dennis Ferguson <dennis@juniper.net>.

Text from PR#5380 for proposed fix:

>Given an htons() macro which compiles to a constant with a constant
>argument the following code fragment avoids generating a 0xffff
>checksum, produces a correct checksum in all cases, avoids the #if's,
>and does the operation with a single comparison and addition on
>machines of either byte order.
>
>	ip->ip_ttl -= IPTTLDEC;
>	if (ip->ip_sum >= htons(0xffff - (IPTTLDEC << 8))) {
>		ip->ip_sum += htons(IPTTLDEC << 8) + 1;
>	} else {
>		ip->ip_sum += htons(IPTTLDEC << 8);
>	}


-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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