Re: [tsvwg] RDMA Support by UDP FRAG Option

[Tom Herbert <[e-mail]>]

On Sun, Jun 20, 2021, 8:58 PM Joseph Touch <[e-mail]> wrote:

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> On Jun 20, 2021, at 8:43 PM, Tom Herbert <[e-mail]> wrote:
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> On Sun, Jun 20, 2021, 8:04 PM Joseph Touch <[e-mail]> wrote:
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>>
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>> On Jun 20, 2021, at 6:24 PM, Tom Herbert <[e-mail]> wrote:
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>> …
>>
>> Length  is the length  in octets  of this user datagram  including  this
>> header  and the data.   (This  means  the minimum value of the length is
>> eight.)
>>
>>
>> Please stop repeating any claim to the contrary, except to note an error
>> in an existing implementation (which should be corrected, not propagated).
>>
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> I am describing how real implementation actually *works*.
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> I do not doubt that, but you *are* propagating an error.
>

That is your opinion.


> There is no error because the correct checksum per RFC768 can be produced.
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> That logic is equivalent to “we do math in base 6” because you only ever
> tried to add 2+2=4.
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> It’s both faulty as logic and incorrect.
>

No, it's not. The algorithms I described are provably correct. One's
complement addition is commutative and associative so:

Sum (whole_packet_from_UDP_header) = Sum(UDP_packet) + Sum(Surplus_area)

So if Sum(Surplus_area == 0) then Sum (whole_packet_from_UDP_header) =
Sum(UDP_packet), and therefore rather an offload performs the computation
over the just the UDP packet or includes the surplus area they get the same
correct result.

Tom


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> Joe
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