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

[Joe Touch <[e-mail]>]

Oh - catching up, using LEN as a flag seems a lot simpler (I thought the proposal was to reuse one of the KIND values).

I personally like the use of LEN=255 for this purpose rather than LEN=0; it seems more meaningful (the highest value means “go longer”)…

Joe

> On Jul 18, 2019, at 7:03 AM, Joe Touch <[e-mail]> wrote:
> 
> We can - there are a few ways to do this:
> - pick one KIND and let it say that the next 3 bytes indicate the next KIND and 2-byte length
> - use a subset of the range of KINDs, reserved in advance, for this purpose
> 
> Note that code points are already assigned to mimic TCP:
> 0 is already in use
> 254 is already reserved for experiments
> 255 is already reserved, likely to extend the KIND space itself
> 
> It might be reasonable to use 255 for this purpose because it inherently extends the KIND space anyway.
> 
> Joe
> 
>> On Jul 18, 2019, at 5:45 AM, Gorry Fairhurst <[e-mail]> wrote:
>> 
>> 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, [e-mail] 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:[e-mail]]
>>>> 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, [e-mail] 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:[e-mail]] De la part de Gorry
>>>> Fairhurst
>>>>>> Envoyé : jeudi 18 juillet 2019 12:22
>>>>>> À : [e-mail]
>>>>>> 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
>> 
>