A Longitudinal View at the Adoption of Multipath TCP

TL;DR

This paper provides a comprehensive longitudinal analysis of MPTCP adoption, revealing increasing deployment but limited real-world usage, and highlights the impact of middleboxes on MPTCP performance.

Contribution

It offers the first in-depth analysis of MPTCPv1 deployment and examines the effects of middleboxes on MPTCP traffic and application quality.

Findings

MPTCPv0 IPs increased 2x in a year, reaching over 13,000 in IPv4.

MPTCPv1 deployment remains low, with about 100 hosts, mainly Apple.

Middleboxes can mirror TCP options and negatively impact MPTCP performance.

Abstract

Multipath TCP (MPTCP) extends traditional TCP to enable simultaneous use of multiple connection endpoints at the source and destination. MPTCP has been under active development since its standardization in 2013, and more recently in February 2020, MPTCP was upstreamed to the Linux kernel. In this paper, we provide an in-depth analysis of MPTCPv0 in the Internet and the first analysis of MPTCPv1 to date. We probe the entire IPv4 address space and an IPv6 hitlist to detect MPTCP-enabled systems operational on port 80 and 443. Our scans reveal a steady increase in MPTCPv0-capable IPs, reaching 13k+ on IPv4 (2$\times$ increase in one year) and 1k on IPv6 (40$\times$ increase). MPTCPv1 deployment is comparatively low with $\approx$100 supporting hosts in IPv4 and IPv6, most of which belong to Apple. We also discover a substantial share of seemingly MPTCP-capable hosts, an artifact of middleboxes mirroring TCP options. We conduct targeted HTTP(S) measurements towards select hosts and find that middleboxes can aggressively impact the perceived quality of applications utilizing MPTCP. Finally, we analyze two complementary traffic traces from CAIDA and MAWI to shed light on the real-world usage of MPTCP. We find that while MPTCP usage has increased by a factor of 20 over the past few years, its traffic share is still quite low.