[dr_hooo]

In MPTCP each connection from the bundle appears/behaves just like a single "traditional" TCP connection. Therefore - at least in theory - there should be no issues with NAT/middleboxes. In fact this has been a major design goal from the start.

[toast0]

MPTCP uses new TCP options. Middleboxes could mess those up.

OTOH, last I heard, Apple uses MPTCP for Siri, so you've got a popular use with a strong influence on mobile networks, that's going to be pushing for at least safe fallback, if not actually working.

[jeroenhd]

I think that's great until those middleboxes start trying to parse TLS headers. TLS 1.3 looks like TLS 1.2 because of the same protocol ossification problem.

There will be issues with middleboxes, but in my opinion middleboxes have been given more than enough time to stop freaking out about network interception after the problem with TLS 1.3 was discovered.

The Red Hat people primarily seem to focus on this as a backend/server-to-server communication method which means that MPTCP (or SCTP) can be rolled out without too much trouble. A big problem SCTP has is that there is no good implementation outside Linux, and even on Linux performance is suboptimal. MPTCP can be linked into the application at runtime (https://github.com/ngi-mptcp/curl/wiki/Multipath-TCP-on-Wind...) so that's not necessarily an issue here, which helps.