Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-ospfv3-segment-routing-extensions-20: (with DISCUSS and COMMENT)

Peter Psenak <ppsenak@cisco.com> Tue, 08 January 2019 16:09 UTC

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To: Benjamin Kaduk <kaduk@mit.edu>
References: <154398144445.4943.7198735398003216566.idtracker@ietfa.amsl.com> <5C079200.1030701@cisco.com> <20181217055358.GC94620@kduck.kaduk.org> <69190220-4994-f9c9-4adf-5016abf3a39b@cisco.com> <03e6354b-c606-fc4a-bbf2-3d59fa1cb774@cisco.com> <20181222042939.GW94620@kduck.kaduk.org> <8D31ADF0-FA83-4B23-805E-76145BF914C1@cisco.com> <f3dff5f1-434c-431d-15a3-5fa7462f5572@cisco.com> <20190108143354.GX28515@kduck.kaduk.org>
Cc: "Acee Lindem (acee)" <acee@cisco.com>, The IESG <iesg@ietf.org>, "draft-ietf-ospf-ospfv3-segment-routing-extensions@ietf.org" <draft-ietf-ospf-ospfv3-segment-routing-extensions@ietf.org>, "aretana.ietf@gmail.com" <aretana.ietf@gmail.com>, "lsr-chairs@ietf.org" <lsr-chairs@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
From: Peter Psenak <ppsenak@cisco.com>
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Date: Tue, 8 Jan 2019 17:09:01 +0100
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Subject: Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-ospfv3-segment-routing-extensions-20: (with DISCUSS and COMMENT)
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Hi Benjamin,

Happy New Year!

Please see inline:

On 08/01/2019 15:33 , Benjamin Kaduk wrote:
> Hi Peter,
>
> Happy new year, and my apologies to all for the heavy overlap between this
> message and the reply to Acee sent just a few moments ago.
> (inline)
>
> On Tue, Jan 08, 2019 at 09:13:52AM +0100, Peter Psenak wrote:
>> Hi Benjamin,
>>
>> please see inline:
>>
>>
>> On 22/12/2018 15:34 , Acee Lindem (acee) wrote:
>>> Hi Ben,
>>>
>>> See inline.
>>>
>>> ´╗┐On 12/21/18, 11:29 PM, "Benjamin Kaduk" <kaduk@mit.edu>; wrote:
>>>
>>>     On Thu, Dec 20, 2018 at 01:07:59PM +0100, Peter Psenak wrote:
>>>     > Hi Benjamin,
>>>     >
>>>     > are you ok with my responses and proposed changed text for the range?
>>>     >
>>>     > thanks,
>>>     > Peter
>>>     >
>>>     > On 17/12/2018 12:32 , Peter Psenak wrote:
>>>     > > Hi Benjamin,
>>>     > >
>>>     > > please see inline (##PP):
>>>     > >
>>>     > > On 17/12/2018 06:53 , Benjamin Kaduk wrote:
>>>     > >> Sorry for the slow reply -- you caught me right as I was leaving for
>>>     > >> vacation.
>>>     > >>
>>>     > >> On Wed, Dec 05, 2018 at 09:53:20AM +0100, Peter Psenak wrote:
>>>     > >>> Hi Benjamin,
>>>     > >>>
>>>     > >>> please see inline:
>>>     > >>>
>>>     > >>> On 05/12/18 04:44 , Benjamin Kaduk wrote:
>>>     > >>>> ----------------------------------------------------------------------
>>>     > >>>> DISCUSS:
>>>     > >>>> ----------------------------------------------------------------------
>>>     > >>>>
>>>     > >>>> What is the extensibility model for the "AF" (address family) field
>>>     > >>>> in the
>>>     > >>>> OSPFv3 Extended Prefix Range TLV?  That is, what do we need to say
>>>     > >>>> about
>>>     > >>>> current implementations' behavior to allow future changes?  (I also a
>>>     > >>>> little bit wonder if we really need a full eight bits, but that's
>>>     > >>>> basically
>>>     > >>>> aesthetic.)
>>>     > >>>
>>>     > >>> I don't think OSPFv3 will ever support other then IPv6 or IPv4 AF. Also
>>>     > >>> the text says:
>>>     > >>>
>>>     > >>> "Prefix encoding for other address families is beyond the scope
>>>     > >>>   of this specification."
>>>     > >>
>>>     > >> Perhaps it would be better encoded in a 1-bit field (rather than an 8-bit
>>>     > >> one), then?  That would at least make the (lack of) semantics of the
>>>     > >> other
>>>     > >> 7 bits more clear, as the usual "MUST set to zero on transmit and
>>>     > >> ignore on
>>>     > >> receipt".
>>>     > >
>>>     > > ##PP
>>>     > > it's too late now to change the encoding. This draft has several years
>>>     > > of history and there are implementation shipping. Changing the encoding
>>>     > > would cause the backward compatibility issues.
>>>
>>>     I didn't think I was suggesting changing the bits on the wire -- in an
>>>     8-octet field, we're encoding the values 0 and 1 as:
>>>
>>>     00000000
>>>     00000001
>>>
>>>     I'm proposing to change the eight bits to be specified as "the first seven
>>>     bits are always set to 0 but should be ignored on receipt; the eighth bit
>>>     represents the 0 or 1 value".  This makes it clear what needs to happen if
>>>     there's a need to use any of those seven bits (an Update to this document)
>>>     and also makes it more clear that there are not expected to be any
>>>     additional AFs defined anytime soon.
>>
>> currently the draft only supports 0 and 1. It says:
>>
>> "Prefix encoding for other address families is beyond the scope of this
>> specification."
>
> Well, that would seem to imply that even though this specification doesn't
> touch them, there is a possibility of using this for future additional
> address families.  So I think you need to say more about where it would be
> in scope to do that work; this could involve making a registration in an
> IANA registry for new family types, or a future IETF document that updates
> this one, or probably some other mechanisms that I'm not thinking of right
> now.

The document says:

"Prefix encoding for other address families is beyond the scope
of this specification."

So we do allow new specification to define a new AF if needed for the 
Range TLV. Although we do not see that happening very likely.

>
>> Given that we have other RFCs where 8-bit field is used for AF, can we
>> leave it as we have it please?
>
> There are ways to resolve my discuss position that do not involve changing
> the encoding or its description, yes.  But see above.

so what exactly would help to resolve the discuss?

>
> (And it would make the discussion of how to proceed easier if we had a
> clear and solid answer about whether future extensions should be permitted
> or not.)

We are not precluding future extensions to AF if they happen.

thanks,
Peter


>
> -Benjamin
> .
>