Re: [tsvwg] RDMA Support by UDP FRAG Option

Tom Herbert <tom@herbertland.com> Mon, 21 June 2021 16:22 UTC

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From: Tom Herbert <tom@herbertland.com>
Date: Mon, 21 Jun 2021 09:22:10 -0700
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To: Joseph Touch <touch@strayalpha.com>
Cc: Gorry Fairhurst <gorry@erg.abdn.ac.uk>, TSVWG <tsvwg@ietf.org>
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Subject: Re: [tsvwg] RDMA Support by UDP FRAG Option
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On Mon, Jun 21, 2021, 8:47 AM Joseph Touch <touch@strayalpha.com> wrote:

>
>
> > On Jun 21, 2021, at 7:34 AM, Tom Herbert <tom@herbertland.com> wrote:
> ...
> > IETF standards specify behavior of protocols,
>
> They DEFINE protocols, including their behavior.
>
> > they do not mandate how
> > protocols are implemented.
>
> Agreed, except that the implementation is faulty unless if follows the
> definition.
>
> > An implementation that produces the
> > specified behavior is correct and conformant with the standard.
>
> If the ones you cite always produced correct answers, yes.
>
> But your claim that “I’ve never seen an error” is like saying “but my
> [broken] watch is fine because I only look at it twice a day - at 8am each
> time”.
>

I have NEVER said that, in fact have seen and FIXED many bugs in this area.
You are completely misconstruing my words.


> Just because you never experienced a corner case doesn’t mean your code is
> correct. It means the code hasn’t been sufficiently tested.


> …
> > In my opinion, the best chance for UDP options to be deployable and
> > successful is to require that the surplus area always sums to zero.
>
> When UDP CS==0, OCS provides that capability. When OCS isn’t zero, it
> doesn’t (and cannot) matter to the UDP layer. It should never matter to any
> other layer, because that layer is either entirely inside the UDP data or
> completely encloses the IP packet. There are no protocols that encapsulate
> UDP but not its outer IP; UDP (like all IETF transport protocols) is not
> even defined in the absence of an IP wrapper.
>
> If you have a case you believe falls outside what I’ve just indicated,
> please provide it. I believe it will demonstrate an error in how protocols
> are encapsulated, not an error where OCS will be required when UDP CS == 0.
>

I have provided that, like offloading a transport checksum in UDP
encapsulation.


> Joe