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

[sratliff <sratliff at cisco.com>]

On 10/29/09 3:23 PM, "Alexandru Petrescu" <alexandru.petrescu at gmail.com>
wrote:

> sratliff a écrit :
> [...]
>>> draft-baccelli says:
>>>> Note that while link-local addresses are assumed to be "on link",
>>>> the utility of link-local addresses is limited as described in
>>>> Section 6.
>>> The word "limited" strikes.
>> 
>> 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"?
> 
>>> 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).
> 


"a SHOULD and a SHOULD NOT could give a MAY"....... I don't even know how to
begin to address this.

I'm comfortable with the current state of "SHOULD/MAY/MUST" that's in the
current document. As I said earlier, I think all of this is a tempest in a
teapot. 

Stan


>>> 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.
> 
>>> 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, (2) can't connect
> to the Internet, (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).
> 
> It sounds as we have it completely reverse, and "MAY" may solve it.
> 
> Alex
>