Re: Thinking differently about the site local problem (was: RE: site local addresses (was Re: Fw: Welcome to the InterNAT...))

[John C Klensin <[e-mail]>]

--On Wednesday, 02 April, 2003 11:23 -0500 Keith Moore 
<[e-mail]> wrote:

>> 	Sounds like you both are arguing that the DNS has become
>> 	"embedded" and the applications that use IP are unusable
>> 	without a working DNS.
>
> as a practical matter, this was true even in IPv4.  yes, you
> can often use address literals in either v4 or v6 apps, but
> this isn't practical for ordinary users on an ordinary basis.
> and in both v4 and v6, several essential apps (e.g. email, the
> web) have explicit dependencies on DNS.  yes you can use
> address literals in email addresses and URLs but there is no
> assurance that an email address or URL with an address literal
> is equivalent to the same address or URL with a domain instead
> of the address. Both email and the web define their resources
> in relation to a DNS name, not relative to a host or address.

At least in the case of email, it is important to be precise 
about this, because we have a clear evolutionary trend:

	(i) RFC 2821 can be read (and was intended to be read)
	to prohibit the use of an address literal in a HELO or
	EHLO command unless the relevant host has no DNS name.
	(sections 3.6, 4.1.1.1, 4.1.4)
	
	(ii) The use of address literals is described as a
	mechanism to bypass a barrier, not one for normal use
	(RFC2821, section 4.1.3)
	
	(iii) On the other hand, the address literal "should"
	still be provided in the From clause of a Received
	field.  Received field information is expected to not be
	picked up by other software and protocols, but the
	inclusion of address information there is very
	leak-friendly.

Contrast this with RFC 821, which doesn't seem to strongly argue 
that explicit address use is undesirable.


> of course it is possible to write apps that do not use DNS,
> but this is rarely done.

Yep.  And as pointed out earlier, we have pushed back strongly 
against such protocol proposals and implementations.

     john