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

2010-02-09 13:26:48
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

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