Re: [GROW] Genart last call review of draft-ietf-grow-bgp-gshut-11

[David Farmer <[e-mail]>]

On Tue, Oct 10, 2017 at 7:33 AM, <[e-mail]> wrote:

> > From: Job Snijders [mailto:[e-mail]]
>  > Sent: Tuesday, October 10, 2017 2:00 PM
> >
>  > On Tue, Oct 10, 2017 at 11:41:32AM +0000, [e-mail]
> wrote:
>  > >  > Any attribute (origin, as_path, aggregator) anywhere can be
> overloaded
>  > >  > to mean something only significant to the local network. I think
> the
>  > >  > document is simpler without this and see no point in mentioning
> this. I
>  > >  > propose:
>  > >  >
>  > >  > OLD:
>  > >  >     The LOCAL_PREF value must be lower than the one of the
> alternate
>  > >  >     path. 0 being the lowest value, it can be used in all cases,
> except
>  > >  >     if it already has a special meaning within the AS.
>  > >  > NEW:
>  > >  >     The LOCAL_PREF value SHOULD be lower than any of the
> alternative
>  > >  >     paths. It is RECOMMEND to use 0, the lowest LOCAL_PREF value.
>  > >
>  > > What is really needed is "The LOCAL_PREF value SHOULD be lower than
>  > > the one of the alternative path." Looks reasonable to extend it to
>  > > your proposition " The LOCAL_PREF value SHOULD be lower than any of
>  > > the alternative paths." So I'm changing for this.
>  > >
>  > > Now the value is truly local to an AS, and I'm not sure to see the
>  > > technical reason to RECOMMEND (SHOULD) a specific value. MAY seems
>  > > more appropriate to me. Hence I'm proposing to keep "Zero being the
>  > > lowest value, it MAY be used whichever LOCAL_PREF values are used by
>  > > the AS."
>  >
>  > So the total of the new text is as following?
>  >
>  >     "The LOCAL_PREF value SHOULD be lower than any of the alternative
>  >     paths.  Zero being the lowest value, it MAY be used whichever
>  >     LOCAL_PREF values are used by the AS."
>
> Yes, that is correct.
>
>  > I am not sure about the second sentence, it seems hard to read.
>
> I'm open to reformulation.
>
>  > I see value in just recommending a value for people moving between ASNs
>  > (debugging other organisation's networks via BGP looking glasses) to
>  > recognise as a highly undesirable path.
>
> I agree.
>
> > Reading RFC 2119 the
>  > 'RECOMMENDED' seems appropiate, "use 0 unless you have a reason not to".
>
> I'm fine with that part, but the subsequent RFC 2119 text "but the full
> implications must be understood and carefully weighed before choosing a
> different course." seems too strong for me, as there is just no issue with
> an AS choosing a different value.
>
>
>  > This is a GROW document and I believe clear-cut guidance will benefit
>  > all.
>
> OK. What about using lower case "recommended" ?
> Proposed NEW: Zero is the lowest value and MAY be used whichever
> LOCAL_PREF values are used by the AS, hence the use of LOCAL_PREF 0 is
> recommended.
>
> (possibly adding "for consistency between ASes and implementations" )
>
> Thanks again for your comments.
> Kind regards,
> --Bruno
>

I would prefer a normative RECOMMENDED, the rest of the sentence in
RFC2119, just means you should explain the constraints on the alternatives.
How about something like this;

"The LOCAL_PREF value SHOULD be lower than any of the alternative
paths.  A LOCAL_PREF
value of Zero is RECOMMENDED, however any LOCAL_PREF value lower than all
other LOCAL_PREF values used within an AS is an acceptable alternative.
The LOCAL_PREF value used, Zero or otherwise, SHOULD NOT also
have another use or meaning within the AS."

-- 
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