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Date:      Tue, 12 Mar 2002 21:41:42 -0500
From:      "Louis A. Mamakos" <louie@TransSys.COM>
To:        mark tinguely <tinguely@web.cs.ndsu.nodak.edu>
Cc:        alpha_byte@centras.lt, ryan@sasknow.com, freebsd-net@FreeBSD.ORG
Subject:   Re: help with tcp checksum 
Message-ID:  <200203130241.g2D2fgY28844@whizzo.transsys.com>
In-Reply-To: Your message of "Tue, 12 Mar 2002 09:38:34 CST." <200203121538.g2CFcYA03380@web.cs.ndsu.nodak.edu> 
References:  <200203121538.g2CFcYA03380@web.cs.ndsu.nodak.edu> 

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> 
> just a PS reminder that you need to put the IP/ports in network byte
> order. appropriate htonl() and htons() must be used if the the values
> are not already in network byte order. You may get away with not doing
> this on a Sparc (or Alpha?) because of their endian is network byte
> order.

This actually isn't necessary, as long as you do all the math on
the fields in the same byte order.  Since 1's complement arithmetic
used to compute the Internet checksum includes end-around carry, it 
just works out.

louie

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