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Re: [dnsext] [spfbis] Obsoleting SPF RRTYPE

Scott Kitterman <spf2@kitterman.com> Fri, 26 April 2013 15:09 UTC

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From: Scott Kitterman <spf2@kitterman.com>
To: spfbis@ietf.org, "dnsext@ietf.org" <dnsext@ietf.org>
Date: Fri, 26 Apr 2013 11:09:17 -0400
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Cc: Ted Lemon <Ted.Lemon@nominum.com>
Subject: Re: [dnsext] [spfbis] Obsoleting SPF RRTYPE
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On Friday, April 26, 2013 07:52:29 AM Murray S. Kucherawy wrote:
> > 2. Because TXT records aren't specific to SPF, a query for TXT records may
> > return an unexpectedly large result set, requiring fallback to TCP.
> > Rejoinder: doesn't seem to be an issue in practice.
> 
> That's not correct; there are still packet filters out there configured by
> default to disallow TCP over port 53.  We discovered this during the
> RFC6686 surveys.

And, in the event a domain needs enough other TXT data that an SPF record 
would cause it to spill over into TCP, it's trivially solvable.  For 
example.com:

example.com.     3600    IN      TXT     "v=spf1 redirect=_spf.example.com"
_spf.example.com. 3600   IN      TXT     "v=spf1 [record content] -all"

It needn't ever be more impact than that.

Scott K

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