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

2010-02-09 06:13:45


On Mon, 8 Feb 2010, John R Levine wrote:

ISP in the UK.  Can you describe the DNS changes needed if they were
publishing a spam button address?
$ dig  mail.btinternet.com a
;; ANSWER SECTION:
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(_at_)yahoo(_dot_)com

Nope, that won't work.  CNAMEs don't do a partial match.

_report.pop-smtp.bt.mail.fy5.b.yahoo.com IN TXT   
abuse-report(_at_)yahoo(_dot_)com
_report.pop-smtp.bt.mail.yahoo.com IN TXT   abuse-report(_at_)yahoo(_dot_)com
_report.mail.btinternet.com IN TXT   abuse-report(_at_)yahoo(_dot_)com

That won't work, either.  You can't have DNS records below a CNAME.

By the way, I was wrong about SRV records. This DNS hack just doesn't work, but it won't work much more elegantly with RP records. See RFC 1183.


What is the objection to attaching the TXT record to the A record? I realize that it means that a single arf-reporting system must serve several CNAMEs, but that is a common requirement for many network services, and I rarely see complaints about it.

Daniel Feenberg

Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
"I dropped the toothpaste", said Tom, crestfallenly.
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