Before we finalized the specs we did a lot of testing to make sure that enabling MPTCP wouldn't break connectivity. Either it would be passed correctly, or it

Before we finalized the specs we did a lot of testing to make sure that enabling MPTCP wouldn't break connectivity. Either it would be passed correctly, or it would fall back to single-path TCP safely. Generally, so long as a middlebox passes through unknown options unmodified, and does not try to enforce that the TCP sequence space it sees is contiguous, MPTCP should work through that middlebox. If you're interested, we wrote a couple of papers on this: [1] https://www.usenix.org/conference/nsdi12/technical-sessions/presentation/raiciu https://www.usenix.org/conference/nsdi12/technical-sessions/... [2] https://www.researchgate.net/publication/229002024_Is_it_still_possible_to_extend_TCP https://www.researchgate.net/publication/229002024_Is_it_sti...