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Re: [tsvwg] Options larger than 255 (was RE: draft-ietf-udp-options issues from IETF 104)

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Thu, 18 July 2019 12:45 UTC

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Date: Thu, 18 Jul 2019 13:45:03 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Subject: Re: [tsvwg] Options larger than 255 (was RE: draft-ietf-udp-options issues from IETF 104)
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Ah so, I guess the document editors canm work out what is best to do.

My wish was to systematically allow larger options to be possible.

Gorry

On 18/07/2019, 13:41, mohamed.boucadair@orange.com wrote:
> Re-,
>
> 0/1 are illegal values. These values MUST NOT be used. A receiver will discard them systematically.
>
> With the proposed approach: 254/255 are legal values... but with a special meaning.
>
> Cheers,
> Med
>
>> -----Message d'origine-----
>> De : Gorry Fairhurst [mailto:gorry@erg.abdn.ac.uk]
>> Envoyé : jeudi 18 juillet 2019 14:26
>> À : BOUCADAIR Mohamed TGI/OLN
>> Objet : Re: Options larger than 255 (was RE: [tsvwg] draft-ietf-udp-
>> options issues from IETF 104)
>>
>> I don't mind the choice of codepoint, my understaning was zero was an
>> invalid length, and an easy thing to test in code. Choosing 254 or 255
>> seems less obvious to me, but if there are good reasons, just say...
>>
>> Gorry
>>
>> On 18/07/2019, 12:48, mohamed.boucadair@orange.com wrote:
>>> Re-,
>>>
>>> Associating a meaning with Len=0 as proposed by Joe may not be
>> intuitive. An alternate approach would be:
>>> * 'Len' only covers the option data field (that is, 'kind' and 'Len'
>> fields are not covered. The overall option length can be easily inferred).
>>> * Associate a meaning with one of the two values we grabbed:
>>>    - 254 or 255: a 16-bit extended length field follows
>>>
>>> Cheers,
>>> Med
>>>
>>>> -----Message d'origine-----
>>>> De : tsvwg [mailto:tsvwg-bounces@ietf.org] De la part de Gorry
>> Fairhurst
>>>> Envoyé : jeudi 18 juillet 2019 12:22
>>>> À : gorry@erg.abdn.ac.uk
>>>> Cc : tsvwg
>>>> Objet : Re: [tsvwg] draft-ietf-udp-options issues from IETF 104
>>>>
>>>>> Gorry
>>>> P.S. I like the idea to explicitly allow options longer than 255 bytes?
>>>> - This seems useful for fragmentation and would be an easy addition,
>>>> someone suggested using 0 option length to indicate a 16b length field,
>>>> which could make total sense. As in:
>>>>
>>>> https://mailarchive.ietf.org/arch/msg/tsvwg/B4oeZkpagdl4gkAMDCFW7F1A7_8
>>>>
>>>> Gorry

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