Type 42
DNS Type 42 · APL
IANA DNS resource record TYPE 42 = APL (Address Prefix List), defined in RFC 3123 (Experimental, June 2001).
RFC 3123 defines the APL record, a list of network address prefixes kept in DNS. It says an APL record has the DNS type of APL and a numeric value of 42. The IANA DNS Parameters registry lists TYPE 42 as APL, reference RFC 3123. Its neighbors are OPT at 41 and DS at 43.
What it supports
An exact assigned number in the DNS record catalogue with its own job: storing lists of address prefixes. It joins port 42 (naming), IP protocol 42 (routing), ICMP type 42 (probing), and TLS alert 42 (certificates) as a separate IANA seat.
What it does not
Not an Internet standard (RFC 3123 is Experimental) and not a claim of wide use. Not DNS port 53. Not APL the programming language. Not IANA port 42 or IP protocol 42 collapsed into this plate. Not Adams.
ExactnessExact
Form42
UnitDNS RR type
Strengthhard
When2001
Hung5 October 2026