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Multipath TCP (MPTCP), standardized in RFC8684 [1], is a TCP extension that enables a TCP connection to use different paths. It allows a device to make use of multiple interfaces at once to send and receive TCP packets over a single MPTCP connection. MPTCP can aggregate the bandwidth of multiple interfaces or prefer the one with the lowest latency, it also allows a fail-over if one path is down, and the traffic is seamlessly re-injected on other paths. To benefit from MPTCP, both the client and the server have to support it. Multipath TCP is a backward-compatible TCP extension that is enabled by default on recent Linux distributions (Debian, Ubuntu, Redhat, ...). Multipath TCP is included in the Linux kernel since version 5.6 [2]. To use it on Linux, an application must explicitly enable it when creating the socket: int sd = socket(AF_INET(6), SOCK_STREAM, IPPROTO_MPTCP); No need to change anything else in the application. This patch allows MPTCP protocol in the Socket unit configuration. So now, a <unit>.socket can contain this to use MPTCP instead of TCP: [Socket] SocketProtocol=mptcp MPTCP support has been allowed similarly to what has been already done to allow SCTP: just one line in core/socket.c, a very simple addition thanks to the flexible architecture already in place. On top of that, IPPROTO_MPTCP has also been added in the list of allowed protocols in two other places, and in the doc. It has also been added to the missing_network.h file, for systems with an old libc -- note that it was also required to include <netinet/in.h> in this file to avoid redefinition errors. Link: https://www.rfc-editor.org/rfc/rfc8684.html [1] Link: https://www.mptcp.dev [2]