Protocol 42
IP Protocol 42 · SDRP
Recorded
IANA Assigned Internet Protocol Number 42 = SDRP (Source Demand Routing Protocol), carried per RFC 1940.
IANA Protocol Numbers lists decimal 42, keyword SDRP, Source Demand Routing Protocol. RFC 1940 says SDRP packets ride as the data of an IP packet with protocol number 42. This is the routing seat beside port 42. DNS record type 42 is a different object.
What it supports
A third IANA series seat at 42: naming is the port, prefixes are the resource record, routing is this protocol number. A hard catalogue fact, with a named protocol and a primary RFC.
What it does not
Not a claim of wide deployment today. Not the same object as IANA port 42 or DNS APL. Not Adams.
ExactnessExact
Form42
UnitIP protocol number
Strengthhard
Hung26 September 2026