From owner-freebsd-hackers  Thu Sep 20 20:40:15 2001
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Date: Thu, 20 Sep 2001 22:34:31 -0500
From: Matt Finlay <matt@ipperformance.com>
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To: Les Biffle <les@safety.net>
Cc: davep@afterswish.com, Alfred Perlstein <bright@mu.org>,
	hackers@FreeBSD.ORG
Subject: Re: sendto not sending what I asked...
References: <200109210250.f8L2oO615274@ns3.safety.net>
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Les Biffle wrote:

> >       pkt.ipbit.ip_sum=in_cksum((unsigned short*)(void*)&pkt,20);
> >       pkt.tcpbit.th_sum=tcpsum(&pkt.ipbit);
>
> You need to do the TCP checksum first.  It changes the payload (the TCP
> checksum).  The IP checksum includes all data, so must be done after the
> payload changes are done.

i think this is incorrect.  the IP checksum only includes the IP header and
any IP options.  therefore order should not matter.


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