RE: about the ULID in the TCP checksum

["Henderson, Thomas R" <thomas.r.henderson@boeing.com>]

> -----Original Message-----
> From: Iljitsch van Beijnum [mailto:iljitsch@muada.com] 
> Sent: Wednesday, January 03, 2007 7:59 AM
> To: Brian E Carpenter
> Cc: shim6-wg
> Subject: Re: about the ULID in the TCP checksum
> 
<snip>
> If this is a problem, it's probably better to adjust the checksum  
> such that it appears to be correct to a non-shim6 aware observer.  
> This does have the downside that incorrect address rewriting isn't  
> detected by the checksum, though.
> 

Why not both twiddle the checksum at the shim so that it is aligned with
locators, and de-twiddle when deshimming?

The implementation is fairly straightforward, to subtract off the ULID
components of the checksum and add back the locator components (and vice
versa).  We've done this for our HIP implementation when substituting
HITs for IP addresses, in certain configurations.

Tom