Re: [Asrg] overloading server names doesn't work, was who has the message

Dave CROCKER <dcrocker@bbiw.net> Tue, 09 February 2010 16:50 UTC

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Date: Tue, 09 Feb 2010 08:51:19 -0800
From: Dave CROCKER <dcrocker@bbiw.net>
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To: John R Levine <johnl@taugh.com>
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Subject: Re: [Asrg] overloading server names doesn't work, was who has the message
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On 2/9/2010 8:40 AM, John R Levine wrote:
>>>>> mail.btinternet.com. 600 IN CNAME pop-smtp.bt.mail.yahoo.com.
>>>>> pop-smtp.bt.mail.yahoo.com. 1800 IN CNAME
>>>>> pop-smtp.bt.mail.fy5.b.yahoo.com.
>>>>> pop-smtp.bt.mail.fy5.b.yahoo.com. 300 IN A 217.12.13.134
>>>>> pop-smtp.bt.mail.fy5.b.yahoo.com. 300 IN A 217.146.188.192
>>>>
>>>> I don't hack DNS records enought to be sure, but it appears to need
>>>> exactly one new record:
>>>>
>>>> _report.pop-smtp.bt.mail.fy5.b.yahoo.com IN TXT abuse-report@yahoo.com
>>>
>>> Nope, that won't work. CNAMEs don't do a partial match.
>> Then I guess it's lucky I didn't specify one.
>
> But you did. The CNAME only matches its exact name, and doesen't do a
> partial match of names below it. RFC 2181 explains this, albeit not very
> clearly.

Where did I or anyone else specify a partial match?


>>>> _report.pop-smtp.bt.mail.fy5.b.yahoo.com IN TXT abuse-report@yahoo.com
>>>> _report.pop-smtp.bt.mail.yahoo.com IN TXT abuse-report@yahoo.com
>>>> _report.mail.btinternet.com IN TXT abuse-report@yahoo.com
>>>
>>> That won't work, either. You can't have DNS records below a CNAME.
>>
>> I'm not finding where that restriction specified among the list of
>> restrictions I can find, and apparently all of popular the summaries
>> written about CNames have missed it too.
>>
>> Please cite the standards text that specifies it.
>
> Also 2181. I'll go see if there's a clearer explanation somewhere else.

Normally, something finer-grained that a reference to all of 15 pages would be 
expected.

And here it is essential, because I still do not see its specifying what you are 
claiming.

Please cite the specific text that asserts the constraint that you believe makes 
it illegal to have a subdomain name, under a domain with a CNAME.


d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net