In the bad old days introducing a new type was deemed risky because a lot of middleware, such as caches and firewalls had type-specific code. I was wanting to test the claim that most modern middleware is type-oblivious and "just works" with new types. So ideally, it would be a type that doesn't exist or one that has just recently been published. The latest ones are according <http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-4> EUI48 and EUI64 (RFC 7043) and then there are a couple (some which are still draft not even mentioned in the list above) which are still draft or just proposed: NINFO RKEY CDS UR and TA. /** draft-reid-dnsext-zs */ LDNS_RR_TYPE_NINFO = 56, /** draft-reid-dnsext-rkey */ LDNS_RR_TYPE_RKEY = 57, /** draft-ietf-dnsop-trust-history */ LDNS_RR_TYPE_TALINK = 58, /** draft-barwood-dnsop-ds-publis */ LDNS_RR_TYPE_CDS = 59, /** DNSSEC Trust Authorities */ LDNS_RR_TYPE_TA = 32768, Enjoy! jaap