From: David Stevens <[EMAIL PROTECTED]> Date: Fri, 10 Nov 2006 09:54:58 -0800
> The Internet checksum is defined as a 1's-complement sum, so if the > alternate 0 does not have a special meaning in a protocol, then by > 1's-complement arithmetic, 0 == ~0. > So, it looks to me without the remapping that a valid checksum > may also fail, if it is simply computed in a different way (or on a > different > architecture) such that one gets 0 and one gets ~0 as un-modified answers. > Since we're checking for equality on 2's-complement machines, > I think the easiest thing is to still re-map it. Otherwise, instead of > testing > for 0, we have to test for both 0 and ~0 in the validity checks, right? Puzzling :-) Then why is the transformation only performed for UDP in the ipv4 stack? It seems by your logic TCP would need to either do the "if (sum==0) sum=~0;" thing or it would need to accept both "0" and "~0" in the checksum checking path. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
