New ways to verify that Multipath TCP works through your network

The design of Multipath TCP has been heavily influenced by the middleboxes that have been deployed in a wide range of networks, notably in cellular and enterprise networks. Some of these middleboxes like regular NATs interact correctly with Multipath TCP and many Multipath TCP users work behind NATs. However, some middleboxes, such as firewalls or TCP optimisers, terminate TCP connections or interfere with TCP options and thus interact badly with Multipath TCP.

Several tools can be used to verify that Multipath TCP works through a given network. If you have installed a Multipath TCP enabled kernel, you can simply use curl and issue the following command :


The webserver that supports has been configured to send a special response to an HTTP request with the curl User-Agent. If the request is sent over a regular TCP connection, the server replies with :

Nay, Nay, Nay, your have an old computer that does not speak MPTCP. Shame on you!

If the HTTP request is sent over a Multipath TCP connection, the server replies with :

Yay, you are MPTCP-capable! You can now rest in peace.

This is a basic test that if often used to validate the correct installation of a Multipath TCP enabled Linux kernel.

However, many users are interested in simpler tests through a web interface or through a smartphone application. Two young researchers have recently released two useful tools. has been the first website created to verify that Multipath TCP was working correctly. Unfortunately, it is not anymore up and running. Alexander Frommgen and his colleagues at TU Darmstadt have posted an updated version of this website. In addition to verifying that the web page is served over a Multipath TCP connection, the new web site also checks whether Multipath TCP passes correctly through other ports. You can test it at Other tests will be added soon.

Screenshot of

Another option is tracebox. This command-line tool allows to perform traceroute-like tests with different TCP options to verify whether they pass through middleboxes. tracebox works well on Linux and MacOS, but not yet on smartphones.

Raffaele Zullo a student at the University of Napoli in Italy has spent several months at the University of Liege to work with Benoit Donnet. During his internship, he developed a new version of tracebox that runs on Android smartphones. It requires a rooted smartphone, but does not need a Multipath TCP kernel on the smartphone. You can download it from

Screenshot of Tracebox on Android