https://docs.kernel.org/networking/sctp.html
PS the kernel work goes back to 2003!
Though SCTP did find its place as a layer in WebRTC.
My old company/offices had site internet provided by one of the top 50 UK Managed Service Providers. They swapped out the on-site router not many years ago as the fibre to site was being upgraded from 100mbit to gigabit and so a new Juniper firewall with GBE ports was required.
Turns out the newer, faster, shinier, though albeit lower model numbered'd Juniper SRX fundamentally didn't support passing SCTP data and suddenly we lost access to all our remote stuff that used it. Ended up on a call with the MSPs Head of Networks (who was not a stupid person), but their opening gambit was "Are you sure you mean SCTP? Oh. What is that then?"
There was also numerous weird kernel bugs with implementations on CentOS 5, 6 and 7 which all would manage to get themselves into weird states where only a reboot would clear - not really what you want from a multi-endpoint, 'copes and recovers well from network weirdness' tunnelling protocol.
did you file a customer complaint for the device you bought not supporting basic internet protocols? If I look here it mentions "internet" but not TCP or UDP. I'd argue it's false advertising if it actually only supports a percentage of actual internet traffic.
Juniper themselves stated in the manual that this base model device didn't support SCTP, though on ever other level it was faster, more capable and more featureful than the mid-range but much older device it replaced. The MSP didn't have a clue that we (or anyone else for that matter) used SCTP so missed the single footnote mention that the command to enable SCTP forwarding might not be available on some base-level devices.
In their defence, I'm not sure _I'd_ have thought to check if SCTP was supported and I had it running on my network. It works over the internet, it's basically IP, how could it not be suppo---oh.
It's an interesting protocol, but these days I think the internet has ossified so far that you're probably better off relying on hacks like QUIC and MPTCP to get the protocol features that SCTP stood to introduce.
TCP as originally specified had fundamental design flaws too, but the TCP of today has significant differences from the 1981 TCP standard (not the first version of TCP, but the first version to see significant production use).
Certainly there are things that could be done to improve the ecosystem - but why bother when you can just use a reliability layer on top of UDP instead? And these days there's a "standard" solution so you don't even need to compare choices or worry about design flaws affecting just your program: just use QUIC, everybody uses it and if something goes wrong the world will scream and the shared library will be upgraded by the distro.
> TCP/IP communication is currently restricted to a single path per connection, yet multiple paths often exist between peers.
In reality, IP modules of all the hosts and routers can load-balance over a set of all available interfaces, as long as global routing information is available.
Heck. I even tried to add it into git because i was having issues with reliable connectivity with WiFi and 5G (i was in a hotel at that time) while working on a project.
So unless, if there is some reason why people kept giving reasons of not include it. I just do not have a reason to add support for $(name your favorite software)
https://chromium-review.googlesource.com/c/chromium/src/+/63...
Maybe the solution might be something similar… an app asks for a TCP socket, but (if the request matches a policy) it gets an MPTCP socket instead-so you could make apps use MPTCP even if they weren’t compiled to support it.
Maybe you could implement this using LD_PRELOAD/ptrace/eBPF/etc
But the best is to let the app (and their users) controlling that, with a nice option. With Chrome/Firefox/..., we could enable MPTCP per domain for example.
MPTCP being enabled on a server is what makes clients running on Apple devices magically not time out when you walk out of Wi-Fi range or switch to LTE (and is behind the “Wi-Fi Assist” setting/feature). iOS and macOS have had it quietly on by default for years: at first just iCloud etc. used it under the hood but for instance WeChat started enabling it like a decade ago for the improved performance.
With MPTCP, the same TCP session hops networks mid-flight. Without it, these seamless handoffs are at best fast reconnects. It’s one of those Apple things that “just works”; on your Linux server you need to flip it on in `socket()` or look into `mptcpize` last I checked but it’s no big deal. I dont think it’s well supported as a client yet and who knows if Android will ever.
(the “Wi-Fi Assist” toggle in Settings doesn’t enable/disable MPTCP, it is on regardless, but it decides if iOS will spin up a cellular subflow when Wi-Fi starts flaking out. It will use some metered data, hence the user-facing toggle.)
mptcp.io monitors servers supporting MPTCP.
> I dont think it’s well supported as a client yet
It is: by default, NetworkManager will configure MPTCP endpoints, so app can use multiple interfaces (if any). See: https://www.mptcp.dev/pm.html
> who knows if Android will ever
Sadly, it is difficult to talk to people in charge there. A few years ago, they were interested in MPTCP, but it was not available in the official Linux kernel. Now it is, and easily accessible (especially for small actors)... but Google has enough resources to find and use alternatives they fully control.
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majke•3mo ago
Back in Jan I wrote a piece about how to actually use MPTCP
https://blog.cloudflare.com/multi-path-tcp-revolutionizing-c...
But plenty has changed since then. It seems all my complains about the API are now addressed. Maybe it's a good time to actually run with MPTCP again :)
In my private affairs, I realised I need MPTCP less, since I started using tailscale. My SSH sessions tend to last longer when going over it.
Sesse__•3mo ago
matttbe•3mo ago