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[spf-discuss] Re: RFC 4408 <draft-schlitt-spf-classic-02.txt> -- AUTH48 changes

2006-03-31 08:49:12
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Frank Ellermann wrote:
Last minute changes:

== proposed ==
   domain-end       = ( "." toplabel [ "." ] ) / macro-expand
== original ==
   domain-end       = ( "." toplabel ) / macro-expand
==============
Two occurences (9.1 and collected ABNF).  This introduces an
unnecessary incompatibility with an unknown number of existing
SPF and SenderID implementations, for an example see
<http://permalink.gmane.org/gmane.mail.spam.spf.discuss/20813>

First, this change doesn't actually introduce an incompatibility.  The 
changed spec explicitly says that trailing dots should not be published, 
however it allows implementations to accept them when encountered anyway.

As for actually breaking implementations:  M:S:Q doesn't count; it deviates 
from the spec in more than a few aspects and will hopefully be replaced by 
Mail::SPF soon.  As Stuart said, pyspf will normally accept trailing dots.  
As far as I can tell, libspf2 does accept trailing dots.  I haven't 
checked any other libs, though (including libspf).

Therefore I recommend to disregard this proposal, or get a 3rd
opinion from John C. Klensin, the author of RFC 2821 and 3696.

The council has carefully weighted the pros and cons and has concluded 
that, given the warning about publishing trailing dots that has been added 
to the spec, the change benefits more than it does harm.  This is not an 
attempt at "proof by authority", but the issue was controversial on 
spf-discuss and _some_ decision had to be made, so the council members' 
personal opinions played a role.

== proposed ==
   toplabel         = ALPHA / ALPHA *[ alphanum / "-" ] alphanum
                      ; LDH rule (See [RFC3696])
== original ==
   toplabel         = <TLD label as per [RFC3696], Section 2>
                      ; LDH rule plus additional TLD restrictions
==============
This prose specification is rather clumsy.  RFC 3696 is an
informational RFC, not suited for a normative reference.

You do have a point, however we're only "Experimental" (yes, this is an 
excuse, but not necessarily a bad one).

The intention is okay, but at this time there exists no RFC with a 
proper ABNF for the "not only digits" LDH rule for toplabels.

True, however not even HTTP (RFC 2616) specifies in its ABNF grammar what 
constitutes a host name, let alone a TLD.  It refers to RFC 2396, which 
has been replaced by the somewhat recent RFC 3986 ("Uniform Resource 
Identifiers (URI): Generic Syntax"), which in turn just refers to RFC 
1034.

See draft-ietf-usefor-usefor-07 for a first attempt in this direction.

Interesting.  (Going from your earlier pointer in the USEFOR direction, I 
had searched the various drafts for a "toplabel" or equivalent definition 
but couldn't find one, probably because I was in a hurry and accidentally 
skipped usefor-usefor-07.)

But we don't have "label" defined, which is required by the USEFOR 
definition of "toplabel", so we'd have to copy that, too, just for the 
sake of an anal-retentive definition of "toplabel".

I see that the RFC Editor did NOT apply[1] our changes completely (for 
example the changes to the ToC are missing), so we'll have to submit 
another -- hopefully VERY BRIEF -- list of changes.  If someone can come 
up with a TERSE and NOT OVERLY COMPLEX definition of "toplabel" (something 
along the lines of USEFOR's "toplabel" and "label" definitions merged and 
simplified), then perhaps we can include it.

References:
 1. http://archives.listbox.com/1943/200603/0049.html
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