cached NXDOMAIN suppressing subdomain lookup attempts seems like the
way to go, if one refers to a DNSWL in a SPF record.
Are you assuming that whatever does the SPF lookups remembers all of
its previous queries?
that the cache would. The special strict NXDOMAIN cache for use by
DNSxL clients.
So you're expecting something other than a normal DNS cache that
exists now.
If you're doing a special purpose cache, why not do a smarter protocol
between the cache and the master server? As far as the client's
concerned, once you need anything other than a vanilla DNS setup, it's
all new special purpose code anyway.
R's,
John
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