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Re: IPSP & IPv6


Perry,

  There are some who believe that the extra bits used by the format I
posted are not appropriate for low bandwidth links, in particular for
existing 2400 baud radio links currently used to carry TCP/IP.  I
think you will find that not everyone agrees on the layout and use of
the first 32-bits inside the protected data area shown on my diagram.
I certainly heard several different points of view on that in the
IPSP meeting.

  Code to parse these headers is the easy part of IPSP so I don't find
"code sharing" to be a persuasive argument that IPv4 and IPv6 must
have the same packet format.  I'm not against having the same format,
but code sharing doesn't seem like a very solid justification IMHO.

  The allocation of Next-Header/Length/Reserved inside the protected
area as the first 32-bits is MANDATORY for all IPSP usage with IPv6 in
the opinion of the IPv6 implementers meeting.  Also, the IPSP meeting
talked about the first algorithm-dependent field (right after SAID) as
variable length and the IPv6 Implementers want that field to be
variable with the restriction of _always_ being a multiple of 64 bits
(the meaningful data within that field might not be the entire field
size of course since not all algorithms are 64-bit aligned :-).  It is
not clear that IPv4 SP and IPv6 SP are necessarily identical in these
areas.  

  I'm not trying to impede progress, just trying to inform folks of
the IPv4/IPv6 convergence issues so that they can be discussed.  I
think there is uniform consensus amongst all on the principles of
operation, we're just talking about packet format differences as near
as I can tell right now.

Regards,

Ran
atkinson@itd.nrl.navy.mil
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