Re: [tsvwg] Alternative version of the UDP FRAG option

[Gorry Fairhurst <[e-mail]>]

I think I missed something between these emails....

On 18/03/2019, 15:13, Tom Herbert wrote:
> On Mon, Mar 18, 2019 at 7:43 AM C. M. Heard<[e-mail]>  wrote:
>> On Sat, Mar 16, 2019 at 9:06 AM Tom Herbert wrote:
>>> Thinking about this, it occurs to me be that the LITE option isn't
>>> needed. The assumption in the UDP options draft is that a receiver
>>> needs the UDP payload to immediately follow the UDP header, but the
>>> UDP payload can be anywhere in the surplus area as long as it's
>>> aligned to four bytes. A receiver will know how to handle it and
>>> deliver the UDP data to the application (e.g. by maintaining a pointer
>>> to the data).
>>>
>>> So that allows a format like:
>>>
>>> UDP header (Length=8) | Surplus area header | Options | Payload
>>>
>>> The surplus area header contains the header length and a checksum
>>> covering the surplus space (four bytes altogether). The three headers
>>> can thought of as an extended UDP header, so the format becomes:
>>>
>>> Extended UDP header | Payload
>>>
>>> Which looks a whole lot like any other protocol format with a variable
>>> length header such as TCP or IPv4.
>> A major downside to this approach is that is does not let you add
>> "optional to process" options such as MSS, Echo Request, and Echo
>> Response to UDP datagrams that are intended to be processed normally
>> by legacy receivers that do not understand UDP options or the extended
>> UDP header format. You can do that with the option trailer as
>> currently proposed.
Right, so this really re-designs UDP as a sublayer to another transport. 
To me, this looks very like an encaps like DCCP-in-UDP or GRE-in-UDP, 
etc. So this isn't an "option" it's an encapsulation.
> Mike,
>
> The converse is also true. We can't put options in a trailer that
> *must* be processed by the receiver (fragmentation, compression,
> security, etc.).
>
> Tom
Why this? I thought that if you make a request to negotiate to use say 
enhanced integrity checking or some security option, then you can 
require the option to be present at the receiver?
Am I misunderstanding something?

Gorry
>> Mike Heard