> MPTCP port blocked
MPTCP doesn’t use any specific ports. It’s an OSI layer higher than that. It’s part of the TCP protocol itself. So if your firewall routes TCP traffic of a specific port (eg HTTP) already then it’ll route MPTCP along with it too.
MPTCP is a protocol extension that requires cooperation by both peers and all middleboxes. So, if there is a Layer 7 firewall, or DPI/SPI, or TLS termination on the path, and it's not inclined to preserve the MPTCP options, then MPTCP will be disabled.