Re: [Autoconf] issues with draft-baccelli address model

["Charles E. Perkins" <charles.perkins at earthlink.net>]

Hello Alex,

Since you CC:'d me, I feel that it should be O.K.
for me to supply a response.


Alexandru Petrescu wrote:
> > Nonsense. "utility.. is limited" is not the same as "must not be
> > used".
>
> Would you agree to say "the utility of /128 prefixes is limited"?

The utility of /128 prefixes is that using them enables
solutions in all circumstances.

Is that limited?

> > > draft-baccelli says:
> > > > o  A subnet prefix configured on this interface should be of
> > > > length /128.
> > > The link-local prefix of IPv6 LLs is fe80::/10, and not /128.
> >
> > The key word in that sentence is SHOULD. It does not say MUST.
>
> Well, LLs are a SHOULD on many interfaces.  A SHOULD and and a SHOULD
> NOT could give a "MAY":  "a /128 prefix on this interface MAY be /128".
> (and I invite implementers to do it and report back problems thank you).

You seem to have already dismissed the experience of
many implementors on this list.  Moreover, as has been
noted before, MAY != ("SHOULD"+"SHOULD NOT").
In fact it is not helpful at all to understand what is at issue.


> > > draft-baccelli says:
> > > > o  Any [IPv4] subnet prefix configured on this interface should
> > > > be of length /32.
> > > Yet the prefix of the IPv4 LL is 169.254/16, and not a /32.
> >
> > Again, the sentence says SHOULD. Not MUST.
>
> Again, a MAY would be a better fit.

MAY is completely worthless in this context.
It adds almost no information, and absolutely
no practical information.



> > > draft-baccelli says:
> > > > Note that the use of IPv4 link-local addresses [RFC3927] in this 
> > > > context should be discouraged for most applications
> > > "Discouraged" means discouraged.  And which "context"?  The word 
> > > "context" appears precisely once in the draft.
> >
> > Precisely. "Discouraged" means discouraged. It doesn't mean "cannot".
> > And again, the sentence contains the word SHOULD. It does not say
> > MUST.
>
> I believe that "dicouraged" fits better the use of host-based routes
> (the "/128" prefix recommendation) for a variety of reasons, making 
> them limited use too:

> (1) it doesn't scale to large domain, 

How large do you need?


> (2) can't connect to the Internet,

Wrong.

> (3) consumes more ressources than /64-or-shorter prefixes (cycles: 
> instead of average 64 bit comparisons you use a sure 128 bit 
> comparisons, memory: instead of one entry covering several 
> destinations you use an entry for each destination in each router).

Here, I agree.  Perhaps you might evaluate the
cost of the memory.  Compare it to the cost of
imposing more DAD or NUD cycles over the air.

> It sounds as we have it completely reverse, and "MAY" may solve it.

I don't think so.

Regards,
Charlie P.