[rjsw]

Doesn't have to wrap it in UDP. Seems to be just an expectation that firewalls can't handle SCTP directly so you will need to wrap it in something else. Extending a firewall to understand SCTP isn't particularly difficult.

In any case, the SCTP reference implementation in FreeBSD can do RFC 6951 encapsulation, someone could add it to Linux too.

[detaro]

It's specified as wrapping in DTLS/UDP, so implementations have to do that if they want to be interopable. The "just an expectation" is sadly a well-studied fact.

That FreeBSD can do that is neat, but just it doing that is pretty much the answer why a library wouldn't implement it, or at least not as a priority.

[gsnedders]

You then need to try and connect via SCTP and then fallback to SCTP-over-UDP (given Windows/macOS don't support SCTP and you need SYSTEM/root access to create a raw socket to implement it in userland, which is a non-starter), which has a performance cost in a common case (falling back).