Status

Ongoing Work

• Christoph keeps the multipath-tcp.org kernel merged with recent kernel releases as part of his maintainership role for the multipath-tcp.org project, and is refactoring parts of the MPTCP implementation to take advantage of newer kernel or TCP features and to align with upstreaming goals.

• Matthieu is setting up and enhancing code review and build automation using gerrit: https://review.gerrithub.io/q/project:multipath-tcp/mptcp_net-next

• Peter and Mat have published a patch set showing an MPTCP architecture with a separate socket type for the MPTCP connection and using in-kernel TCP sockets for subflows. This prototype can connect, receive, and transmit using a single-subflow IPv4 MPTCP connection. Patches are in git and gerrit (in gerrit, look at the "relation chain" in the upper left part of the page for the patch listing). This patch series has been through several rounds of review, with work in progress to use ULP between the subflow and ULP socket layers.

• Ossama has developed a userspace path manager implementation, will be open sourced shortly.

• Florian has contributed a kselftest implementation.

Future Work

• monitoring: is a good idea with socket diag
• monitoring: is MPTCP working? → ss could answer that
• monitoring: also an entry in /proc/net/mptcp_net/mptcp (like the mptcp.org implem)
• tests with kselftests + packetdrill
• scheduling (via eBPF)
• path-management (via Netlink)
• prototype features: DATA_FIN, coupled receive windows, IPv6
• documentation: Feature roadmap (initial upstream functionality, follow-on features)

Previous Work

• Florian merged skb extension capability in the upstream kernel (

• Matthieu shared a generic netlink patch set to mptcp-dev, and it has been merged to mptcp_trunk

• Ossama shared a generic netlink path management API proposal, which has been discussed and refined to align better with the generic netlink implementation on mptcp_trunk.

• Stephan shared a userspace path manager draft implementation at https://github.com/brenns10/pathmand

• Mat developed an extensible TCP option framework patch, and Christoph refactored upstream TCP-MD5 and SMC functionality to use it. The idea was to integrate some extensions in to TCP that had utility for existing functionality, but would also help integrate MPTCP. This RFC patch set was turned down by Dave Miller, but did give us useful guidance. (Patches in git)

• Mat published a proposal for optionally extending sk_buff shared info to carry MPTCP metadata.

• Rao has published an RFC patch set based on the multipath-tcp.org MPTCP implementation and the current upstream kernel, with modifications to make the TCP implementation extensible in a way that's useful for MPTCP.