Re: [tsvwg] COMMENT PLEASE: Which DSCP value should we use for LE PHB?

[Brian E Carpenter <[e-mail]>]

On 07/07/2017 23:23, Gorry Fairhurst wrote:
> On 07/07/2017, 12:03, Bless, Roland (TM) wrote:
>> Hi Gorry,
>>
>> Am 07.07.2017 um 10:58 schrieb Gorry Fairhurst:
>>> This email is intended to start a discussion about the most appropriate
>>> DiffServ codepoint to assign to the LE PHB specified in:
>>> https://tools.ietf.org/html/draft-ietf-tsvwg-le-phb-02
>>>
>>> The current list of available codepoints is listed by IANA here:
>>> https://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml
>>>
>>> The draft currently suggests using the DSCP value, '000010'.
>> I think it is DSCP value 2.

> That's two indeed:-).

>>> Question 1: Is this codepoint a good choice for the TSVWG group to
>>> assign for the LE PHB?
>>>
>>>    Things to consider:
>>>      - Is the codepoint currently being used for other (non-standard
>>> applications) that may get in the way of the deployment of the LE PHB?
>> Currently, nothing should be using a non-assigned Standard DSCP.
>> I really don't like these discussion along the lines of: oh, probably
>> there are some standard-ignoring boxes/apps out there, so lets try to
>> work around their broken design. So, yes, it's probably good to know,
>> but IMHO it's better to get this other stuff fixed rather than to always
>> create workaround.

> And, I think a more usedful disucssion here is around - "what happens 
> when you use existing codepoints that are IETF-approved, and they pass 
> through the current Internet" - do they emerge as the codepoint you propose?

Since the architecture allows *any* rewriting whatever of the DSCP value
at a domain boundary, I'm not clear why any of this is relevant. The Internet
isn't supposed to be transparent to DSCP values, and all DSCP values are
recommendations anyway. 

It seems to me that RFC8100 resolves the issue about what is expected to
work across domain boundaries; all we are doing here is fixing the historical
misuse of a codepoint.

So 000010 seems like a perfectly fine bit pattern to me.

    Brian
 
>>>      - Is there ant evidence that this DSCP value is less likely to be
>>> forwarded than other unused codepoints?
>>>      - Is this codepoint observed in the wild due to common DSCP-mangling
>>> pathologies (such as ToS-byte bleaching)?
>>>
>>> Question 2: Is there an alternate unassigned codepint that could be
>>> chosen that would give better opprotunities for deployment?
>>>      Things to consider:
>>>      - A codepoint less than 7 appears to have less chance of
>>> DSCP-mangling pathologies (such as ToS-byte bleaching)
>>>      - IANA currently allocates from pool 1 (xxxxx0), but we could
>>> consider asking to use pool 3 ('xxxx01'), e.g., '000001'or '000101'.
>> I don't see any compelling reason to start using another pool right now.

> Don't you? I think this depends on the outcome.

>>> Measurement experience and thoughts on this topic are welcome on the
>>> mailing list ahead of the TSVWG meeting. At this meeting, I would like
>>> to see some discussion confirming the choice of DSCP codepoint or
>>> suggesting a more appropriate codepoint for the working group to request.
>> Thanks for triggering the discussion.
>>
>> Regards,
>>   Roland
> Roland, do you have any measurement data?
> 
> Gorry
> 
>