Re: [Asrg] DNS basics, was overloading server names doesn't work

[Douglas Otis <[e-mail]>]

On 2/9/10 10:34 AM, Dave CROCKER wrote:
> On 2/9/2010 9:11 AM, John R Levine wrote:
>>>>>> Nope, that won't work. CNAMEs don't do a partial match.
>>> Where did I or anyone else specify a partial match?
>> The user thinks his POP server is called mail.btinternet.com. When he
>> looks up _report.mail.btinternet.com, what do you expect to happen?
> He'll get a TXT record back.  This is nothing but exactly the same 
> mechanism that is used for DKIM and SRV, albeit with a different 
> underscore subdomain.
This overlooks an issue created by SPF having defined TXT records 
without prefix labels to permit wildcard use.  A query for 
_report.mail.btinternet.com IN TXT might obtain an unexpected wildcard 
TXT record.  There is no registry related to disambiguating TXT 
records.  When used for DKIM, cryptography attests validity.    There 
might be a better chance for an SRV label registry of being developed.  
SRV records offers a means to establish redirection, having a similar 
effect as a CNAME.

By using SRV records, a receiving domain controls where reports are to 
be sent.  SRV records even allows for load balancing techniques.

-Doug