Multipath TCP support



Apple has added support for Multipath TCP on iOS11 and all applications can leverage this TCP extension to improve user experience. I was wondering whether it was possible for an iOS application using Multipath TCP to interact with CloudFlare servers through Multipath TCP or if Cloudflare was restricted to regular TCP.


Olivier Bonaventure


While I think this would be a great idea that has potential to greatly
increase reliability, I’ve yet to see Multipath TCP actually working in
practice, at least according to

I’ve tested from various local networks with a variety of firewall
configurations and I’ve yet to get a “Yes MPTCP is working” result on
iOS 11.

Have you see MPTCP actually working in the real world from a modern iOS


Most of the networks that I’ve tested support MPTCP. This is true for WiFi networks and many cellular networks. There are exceptions in cellular networks where the operator has deployed a transparent TCP/HTTP proxy. Usually, those middleboxes operate only on ports 80 and 443.

Apple reports very good experience with Multipath TCP and their Siri application.

When you use Safari to reach from an iPhone, you use Safari which is an application that does not use Multipath TCP. If you want to test Multipath TCP, you need to use a specific MPTCP application, see e.g.


I could have sworn I read that MPTCP support was in Safari natively now, but if it is not that definitely explains things. Unfortunately this would seem to severely limit the usefulness of Cloudflare implementing MPTCP since there would be very few situations where it can be used by a typical client unless specifically developed for this support.

On the other hand, chicken-meet-egg, if neither clients nor servers support it then neither clients nor servers will support it. Cloudflare is known for being on the leading edge (TLS 1.3, 0RTT, DOH), it would be very interesting to see Cloudflare’s frontend support MPTCP.


MPTCP would be a very interesting feature in the mobile SDK. With iOS11, there are now a lot of clients which support Multipath TCP and the Linux implementation available from provides the server side.


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