Subject: Migrating away from TXT records

From: Florian Weimer <[email-masked]>
Date: Thu, 11 Aug 2005 19:59:44 +0200

Someone apparently told the SPF folks that when you migrate away from
TXT records to a specifically-assigned record type, you have to
perform a check that records contain identical data when both types
are present.  In other words, if there is a domain name for which both
TXT records and new-type records are present, an implementation MUST
check if both records contain the same data, and it MUST signal a
error if this is not the case.

Unfortunately, this is not a very good idea.  As long as you only
query your local resolver, it is *not* possible to obtain a consistent
cut--which is necessary before you can perform such a consistency
check.  As a result, the check will fail sporadically, for example
when the records are updated, even if the update to both sets happens
in a single zone reload (or whatever means you use to publish DNS
records).

(It turns out that the SPF specification assumes in many places that
DNS inconsistencies are always permanent and never temporary, but this
peculiar approach to DNS probably doesn't concern this WG.)

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