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

On Thu, Mar 21, 2024 at 7:54 AM Robinson, Herbie
<Herbie.Robinson=40stratus.com@dmarc.ietf.org> 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.

Herbie,

In the host it's not a horrible amount of work since extension headers
are mostly independent of the IP protocol and we'll be able to share a
lot of implementation. For instance, supporting Fragment Header in
IPv4 is fairly straightforward, most of the logic dealing with
fragments in reassembly is agnostic to the IP protocol (except for
using the addresses to match fragments to the reassembly queue). I
imagine it's probably less than fifty Lines of Code to support IPv4
Fragment Header in Linux.

Support in routers is already there inasmuch that they can forward
packets of any unresognized IP Protocol. Router support for IPv4 HBH
or the IPv4 flow label is completely optional.

Tom

>
>
>
> From: Int-area <int-area-bounces@ietf.org> On Behalf Of touch@strayalpha.com
> Sent: Thursday, March 21, 2024 10:46 AM
> To: Toerless Eckert <tte@cs.fau.de>
> Cc: int-area <int-area@ietf.org>
> Subject: [EXTERNAL] Re: [Int-area] New Version Notification for draft-herbert-ipv4-eh-03.txt
>
>
>
> [EXTERNAL SENDER: This email originated from outside of Stratus Technologies. Do not click links or open attachments unless you recognize the sender and know the content is safe.]
>
>
>
> ________________________________
>
> On Mar 20, 2024, at 9:35 PM, Toerless Eckert <tte@cs.fau.de> wrote:
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>
>
> 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.:
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>
>
>               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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