Domain Name System (DNS) Parameters
https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtmlDNS | Dataset | IANA
Internet Assigned Numbers Authority (IANA) tracks the assignment of all DNS related constants. This includes available classes, resource records types, OpCodes, RCODEs, and various other values. Each assigned number is linked to the corresponding RFC describing its function. This is a great overview to see which values are available.