Re: Re: Problems with spf testsuite and dns specification

On Sat, 16 Jun 2007, Julian Mehnle wrote:

> > The point is, a live resolver *just might* return multiple identical
> > records.  In that case (as unlikely as it may be in practice), rfc4408
> > says the result is PermError.  So this is a legitimate thing to test
> > for.
> 
> No, it isn't.  Testing it like the test suite currently does means 
> implicitly testing for obeyance or non-obeyance of a "should" in RFC 2181.  
> A resolver (be it live or stub) may very well combine multiple identical 
> records into a single one and NOT be incompliant with RFC 4408!  Or are 
> you saying that using a DNS resolver/cache that conforms to RFC 2181 5/1 
> makes an SPF implementation _incompliant_ with RFC 4408?
> 
> > The more unlikely, the more important to test for it.
> 
> This has nothing to do with probabilities.  Both combining and not 
> combining multiple identical records is legal according to RFC 2181.

That is irrelevant.  What is relevant is that if you see multiple
records, whether identical or not, the 4408 result is PermError.
That 4408 compliance is what we are testing for.  The 2181 behaviour
makes testing trickier when using live DNS, but otherwise is
unrelated.

> But it is obviously relative to RFC 2181 5/1.  _Why_ can a stub resolver 
> (or test suite driver) not conform to RFC 2181 5/1?  I don't see this 
> written anywhere.  Why would using a combining _live_ resolver be legal, 
> whereas using a combining _stub_ resolver would not?

They are both legal.  But 4408 says that when your stub/resolver 
gives you multiple identical records, the result is PermError.
The test suite tests for that very nicely in the case of a stub.
Live DNS is more difficult to test for this case due to 2181 5/1.

This is a testing problem, NOT a "what does the standard say" problem.
The reason to allow both results is not because the standard is
unclear, but because it is too difficult in practice to do the
test properly with live DNS.  Live DNS testing is valuable because it
tests more of the whole system, so making some accomodations for it
is reasonable.  Also, we promised to also support live DNS in the test
suite goals.

-- 
	      Stuart D. Gathman <[email protected]>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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