Multipath TCP is a TCP extension specified in RFC8684 that allows a TCP connection to use different paths such as Wi-Fi and cellular on smartphones or Wi-Fi and Ethernet on laptops. Multipath TCP is supported by Linux kernel versions >5.15 and enabled on many popular distributions.
The utilization of Multipath TCP is negotiated during the TCP three-way handshake. This implies that if a Multipath TCP client contacts a regular TCP server, they will use a regular TCP connection. Similarly, if a regular TCP client contacts a Multipath TCP server, they will use a regular TCP connection. Multipath TCP will only be used if both the client and the server support Multipath TCP.
Two steps are required to use Multipath TCP on a host with a recent Linux kernel. First, the net.mptcp.enabled sysctl variable must be set to 1 :
sysctl net.mptcp.enabled=1
Second, the application must pass IPPROTO_MPTCP as the third parameter of the socket() system call.
The following examples show how enable Multipath TCP with different programming languages:
- Using Multipath TCP in C
- Using Multipath TCP in python
- Using Multipath TCP in perl
- Using Multipath TCP in Rust
If you do not have access to the application's source code, you can use mptcpize to automatically transform the TCP socket system calls into Multipath TCP sockets.
The implementation of Multipath TCP in the Linux kernel is regularly improved. You can track the changes at https://github.com/multipath-tcp/mptcp_net-next/wiki