Re: [tsvwg] draft-ietf-udp-options issues from IETF 104

[Tom Herbert <[e-mail]>]

On Mon, Jul 15, 2019 at 10:40 AM Joe Touch <[e-mail]> wrote:
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> On 2019-07-15 10:27, Tom Herbert wrote:
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> On Mon, Jul 15, 2019 at 10:02 AM Joe Touch <[e-mail]> wrote:
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> On 2019-07-15 09:39, Tom Herbert wrote:
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> On Mon, Jul 15, 2019 at 9:15 AM Joe Touch <[e-mail]> wrote:
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> On Jul 15, 2019, at 8:50 AM, Tom Herbert <[e-mail]> wrote:
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> On Sun, Jul 14, 2019 at 8:52 AM Joe Touch <[e-mail]> wrote:
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> So, *given* that we *are* different from UDP and TCP, i.e., we do NOT have the luxury of a fixed-offset location for this checksum
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> Joe,
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> There's no requirement that precludes defining a fixed header that
> precedes the surplus space.
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> It clearly can't be a fixed location. Thats all I was asserting.
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> Or do you disagree?
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> In draft-herbert-udp-space-hdr-01 the checksum is a header that
> precedes the surplus space.
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> I don't understand why this is confusing, so I'll be blunt:
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> - OCS WILL NOT come at a *fixed offset* from the UDP header
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> Joe,
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> On that I agree. But, draft-herbert-udp-space-hdr-01 proposes to put a
> checksum, which is not OCS, in a fixed header at the beginning of the
> surplus space that covers the whole surplus.
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> Sorry, but you're not following where were are with the UDP options.
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> 1) we already agreed (in the past week) to make the OCS field mandatory
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> 2) OCS always covered the entire option space
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> 3) we already agreed that there would NOT be any surplus space beyond the options, i.e., that options would take up the whole surplus space
> (anyone who wants to use surplus space should coordinate with the UDP options using that mechanism, as I noted when evaluating your proposal as not necessary)
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Please explain how LITE mode works robustly if the UDP checksum is set.

> NOTE: we still can use EOL to halt option processing, but the assumption is that the remainder is *ignored*, not there for other uses. If that's an issue, we can omit EOL.
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> **Given that context**, all that remains regarding OCS now are the following questions (which is why I started with them and hope to get back to):
> - OCS at head or tail of the surplus space
> - OCS aligned, and if so, at what level (16-bit, 32-bit)
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> NOTE1: your claims about offloading driving alignment seem to be undermined by the need for using an untenable 255-byte offset from the beginning of the UDP packet (not the surplus space - whose start offset itself *varies from packet to packet* relative to the UDP header, unlike the UDP checksum).
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> NOTE2: *as repeatedly already noted*, again - GIVEN THIS CONTEXT - there is no utility in the additional pre-option header proposed in draft-herbert-udp-space-hdr-01.
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> Joe
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