Dear colleagues, During RIPE66, I will present a tutorial on Multipath TCP, a major TCP extension that has recently been approved by the IETF (RFC6824). The design of Multipath TCP has been heavily influenced by various types of middleboxes that process/modify/... various fields of the IP/TCP packets. Multipath TCP is in theory capable of handling these middleboxes and either go through or at worst fallback to regular TCP. In order to check this fallback mechanism, we ask your help to perform test behing as many real middleboxes as possible. To ease the testing, we have placed a modified Linux kernel that includes Multipath TCP inside a virtualbox image, added several measurement scripts to automate the test and collect packet traces. The tests run on Linux and MacOS. They do not currently work on Windows. You can download the virtualbox image from : http://multipath-tcp.org/pmwiki.php?n=Users.AboutMeasures The script needs about 15 minutes to complete and you will have access to a trace of all the packets sent and received by your virtualbox and our server if you'd like to check the interference caused by your middleboxes. We'd appreciate tests in networks that are more likely to include middlboxes such as entreprise networks, WiFi hotspots or cellular networks. From a technical viewpoint, the tests use various applications including traceroute, ftp (to trigger NAT ALG), http, https, scp. We use multipath subflows (1 and 4) and a modified Multipath TCP kernel that provides more debugging and also three different schedulers. The first scheduler is the standard MPTCP scheduler that sends packets over the best subflows, a second scheduler that sends packets in strict round robin and a scheduler that copies each packet over all subflows to detect the impact of retransmissions. Since Multipath TCP has never been deployed/tested on a large scale, these tests might trigger some alarms from firewalls/IPS/DPI boxes that could detect unknown behaviour. If this happens, please send a report to Fabien Duchene indicating the type of alarm. All the data collected will be analysed and I plan to report on these results during the tutorial at RIPE66 Thanks for your help, Olivier Bonaventure