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Date:      Mon, 17 Jan 2000 12:28:42 -0500
From:      "Louis A. Mamakos" <louie@TransSys.COM>
To:        Charles Youse <cyouse@paradox.nexuslabs.com>
Cc:        freebsd-hackers@FreeBSD.ORG
Subject:   Re: PR kern/15656 
Message-ID:  <200001171728.MAA19299@whizzo.transsys.com>
In-Reply-To: Your message of "Mon, 17 Jan 2000 11:55:37 EST." <Pine.BSF.4.20.0001171153070.15159-100000@paradox.nexuslabs.com> 
References:  <Pine.BSF.4.20.0001171153070.15159-100000@paradox.nexuslabs.com> 

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> Agreed; however, the PR states that should the checksum be 0xFFFF, the
> complement of which is 0x0000, the checksum should still be sent as
> 0xFFFF.

Ok, I looked at the PR, which seems to refer to the TCP header checksum,
rather than the checksum in the IP header.  So please disregard the specific
pointer to RFC-791.

> Can anyone verify this?  I can verify that BSD sends 0-checksums; I can't
> on Solaris.

For other than the intentional UDP-checksum is zero case (which shouldn't
really occur), the stack shouldn't be sending checksums in the protocol
headers valued 0x0000.  

Looking at the in_cksum code, it would appear that a test at the very
final step might be necessary (if you presume that the intermediate
computations might produce a -0).  But that code is highly tuned, and more
than a cursory examination is called for.

louie




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