Re: [tsvwg] UDP options and header-data split (zero copy)

[Tom Herbert <[e-mail]>]

On Sat, Jul 31, 2021 at 11:34 AM Joseph Touch <[e-mail]> wrote:
>
> Hi, Tom,
>
> On Jul 31, 2021, at 11:27 AM, Tom Herbert <[e-mail]> wrote:
>
> Joe,
>
> You seem to be missing my point. There are implementations that
> terminate UDP and CANNOT process protocol trailers; this is not just
> an inconvenient performance degradation.
>
>
> If that is the case, then they MUST NOT try to support UDP options. See below.
>
If UDP options cannot be used with UDP tunnel protocols, one of the
biggest use cases for UDP, then I believe the protocol is
fundamentally flawed. At the very least this needs to be documented in
the draft, and if UDP options are only meant to be used for certain
use cases that should be contained in an applicability statement in
the draft.

> Yes, that means that they
> can't use legacy mode, but I don't see the technical argument that UDP
> couldn't be productively supported by these implementations if UDP
> options are all contained in headers.
>
>
> Again, support for legacy receivers has always been a requirement of a solution.
>
> I do not believe this is an
> aberration, we know for instance there are HW routers terminating UDP
> tunnels, and it would be a delusion to believe these implementations
> could be fixed to support protocol trailers in a finite time. So if
> protocol trailers are a forced requirement, even in non-legacy mode
> which is what tunnels would use anyway since they're configured, it
> seems like we're excluding use cases such as UDP tunnels where UDP
> options might be compelling. Given this, what is your answer to
> someone who wants to use UDP options with UDP tunnels?
>
>
> There’s no way that endpoint can ensure it never sees non-fragment UDP options, so it cannot support UDP options.
>
For a tunnel, use of UDP options would just be another configuration
parameter at the end points; we don't need negotiation to send
non-legacy packets. If there's a mismatch in endpoint configuration
then the operator simply detects it and fixes it like any other tunnel
configuration problem.

> Joe
>