Cloudflare Talks Up Multi-Path TCP But Dings Linux's Less Than Ideal Support
Multi-Path TCP is a means of allowing a TCP connection to use multiple paths (such as multiple wired/wireless network adapters) for achieving greater throughput and increased redundancy. This is excellent in theory for allowing greater throughput and redundancy especially for mobile phones having both a cellular data connection and WiFi or servers sporting multiple wired network interfaces, but in practice it's still not a fully-baked solution.
As written about back in 2020 on Phoronix, Multi-Path TCP was merged in Linux 5.6 and since then MPTCP has been seeing more improvements within the kernel as well as related Linux networking user-space components.
In the Cloudflare blog post they acknowledge the Linux support as well as the Apple support found with macOS 10.10 and newer or iOS 7 and newer. MPTCP support on Linux is more viable for servers but less ideal with the current client support.
Among the key takeaways from the Cloudflare blog:
"I find MPTCP very exciting, being one of a few deployable serious TCP extensions. However, current implementations are limited. My experimentation showed that the only practical scenario where currently MPTCP might be useful is:
- Linux as a server
- macOS/iOS as a client
- "interactive" use case
With a bit of effort, Linux can be made to work as a client.
Don't get me wrong, Linux developers did tremendous work to get where we are, but, in my opinion for any serious out-of-the-box use case, we're not there yet. I'm optimistic that Linux can develop a good MPTCP client story relatively soon, and the possibility of implementing the Path manager and Scheduler in BPF is really enticing.
Time will tell if MPTCP succeeds — it's been 15 years in the making. In the meantime, Multi-Path QUIC is under active development, but it's even further from being usable at this stage."
Those interested can read the blog post in full by Cloudflare engineer Marek Majkowski.
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