The Domain Name System has always been intended to be extensible. The original spec in the 1980s had about a dozen resource record types (RRTYPEs), and since then people have invented many more so now there are about 65 different RRTYPEs. But if you look at most DNS zones, you’ll only see a handful of types, NS, A, AAAA, MX, TXT, and maybe SRV. Why? A lot of the other types are arcane or obsolete, but there are plenty that are useful. Moreover, new designs like DKIM, DMARC, and notoriously SPF have reused TXT records rather than defining new types of their own. Why? It’s the provisioning crudware. —John Levine @ CircleID
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