Re: [Int-area] New Version Notification for draft-herbert-ipv4-eh-03.txt

[Tom Herbert <[e-mail]>]

On Thu, Mar 21, 2024 at 7:46 AM [e-mail]
<[e-mail]> wrote:
>
> On Mar 20, 2024, at 9:35 PM, Toerless Eckert <[e-mail]> wrote:
>
>
> On Wed, Mar 20, 2024 at 09:20:24PM -0700, Tom Herbert wrote:
>
> In other words, Destination Option Headers do not have fundamentally distinct
> processing requirements on the destination host examining it than any other
> possible protocol header (e.g.: UDP, TCP), or at least we could not find such a description
> for any such guiding rules or treatment differences in RFC8200.
>
>
> Yes, that's mostly how all the IP protocols are implemented.
> Processing of an encapsulated  protocol isn't completely independent,
> for instance the pseudo header for the TCP and UDP checksum is
> different for IPv4 and IPv6.
>
>
> Right. But it seems unrelated to whether or not a header is an extension header,
> TCP and UDP not being extension headers for example.
>
>
> I haven’t seen it mentioned yet (apologies if so), but there is a big difference between extension headers and encapsulated protocols.
>
> Extension headers - no matter how many - can each refer back to the base header. Same for the first encapsulated protocol.
>
> E.g.:
>
> IP1 IP2 IP3 TCP…. TCP uses a pseudo header based on IP3
> But:
> IPv6a EHb EHc TCP… TCP uses a pseudo header based on IPv6a; each of the EH’s can also refer back to IPv6a
>
> I see NO way to do this with any mechanism for IPv4 except options (whose space is limited). There’s no way to redefine protocol processing to ensure that information can be “Carried” forward across EHs.
>
> This seems like a show-stopper; has it been addressed?

Joe,

It already happens in IPv4. Consider the header chain IPv4-AH-TCP. In
practice, host stacks have already accounted for this so I don't see
this as a problem.

Tom

>
> Joe