A first look at Multipath TCP traffic

The Multipath TCP website is a unique vantage point observe Multipath TCP traffic on the global Internet. We have recently collected a one-week long packet trace from this serverL. It has been collected using tcpdump and contains the headers of all TCP packets received and sent by the server hosting the Multipath TCP Linux kernel implementation. Apart from a web server, the machine also hosts an FTP server and an Iperf server. The machine has one physical network interface with two IP addresses (IPv4 and IPv6) and runs the stable version 0.89 of the Multipath TCP implementation in the Linux kernel.

To analyse the Multipath TCP connections in the dataset, we have extended the mptcptrace software . mptcptrace handles all the main features of the Multipath TCP protocol and can extract various statistics from a packet trace. Where necessary, we have combined it with tcptrace and/or its output has been further processed by custom scripts.

The table below summarizes the general characteristics of the dataset. In total, the server received around 136 million TCP packets with 134 GiBytes of data (including the TCP and IP headers) during the measurement period. As shown in the table (in the block Multipath TCP), a significant part of the TCP traffic was related to Multipath TCP. Unsurprisingly, IPv4 remains more popular than IPv6, but it is interesting to note that the fraction of IPv6 traffic from the hosts that are using Multipath TCP (9.8%) is bigger than from the hosts using regular TCP (3.7%). This confirms that dual-stack hosts are an important use case for Multipath TCP.

We have also studied the application protocols used in the multipath TCP traffic. Around 22.7% of the packets were sent or received on port 80 (HTTP) of the server. A similar percentage of packets (21.2%) was sent to port 5001 (Iperf) by users conducting performance measurements. The FTP server, was responsible for the majority of packets. It hosts the debian and ubuntu packages for the Multipath TCP kernel and is thus often used by Multipath TCP users.

In terms of connections, HTTP was responsible for 89.7% of the traffic, Iperf for 6.4%, and FTP control connections for 1.9% and the 2.0% higher ports and are probably FTP data connections.

All TCP Total IPv4 IPv6
# of packets [Mpkt] 136.1 128.5 7.6
# of bytes [GiByte] 134.0 129.0 5.0
Multipath TCP Total IPv4 IPv6
# of packets [Mpkt] 29.4 25.0 4.4
# of bytes [GiByte] 20.5 18.5 2.0

In subsequent posts, we will explore the packet trace and provide additional information about what we have learned about Multipath TCP when analysing it.