On 22-Mar-24 03:53, Robinson, Herbie wrote:
I would say that, in theory, that’s not a show stopper, but in practice it is a 
lot of work to implement – enough to suggest that you wouldn’t get enough 
implementations to make it useable.

I'll say it because nobody else has (recently).

Why should the IETF spend effort on upgrading IPv4 capabilities at this point?

   Brian


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*Sent:* Thursday, March 21, 2024 10:46 AM
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*Cc:* int-area <[email protected]>
*Subject:* [EXTERNAL] Re: [Int-area] New Version Notification for 
draft-herbert-ipv4-eh-03.txt

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On Mar 20, 2024, at 9:35 PM, Toerless Eckert <[email protected] 
<mailto:[email protected]>> 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


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