Raw IP sockets are accessible from the same userspace facing APIs as e.g. UDP sockets and don't require climbing up the stack. Unfortunately operating systems started to consider custom protocol implementations security risks but rather than reverse that thinking we've just continued to abstract up past it.
In reality I think "where it is implemented in code" was a small portion of QUICs design choices compared to "IPv4 NAT & external firewalling has ossified protocols" which is a similar story of "just abstact up to avoid the issues". Unfortunately in that case I don't think abstracting up isn't as permanent a solution as it was on the OS side.
Likewise NAT devices typically support UDP flows today due to their prevalence in games, but if you introduce a new transport protocol at the IP layer, they wouldn't be able to identify which flow (and therefore which NATed endpoint) the packet is destined for.
In reality raw sockets work in a way that the question is the reverse of what you describe. The kernel will check 2 things: - Which raw sockets are bound to the protocol number seen in the packet - Which raw sockets have issued "connect" to the sending IP
Any and all raw sockets that match these will receive the packets. In such a sense the protocol (QUIC) needs to have some way to identify streams so that if e.g. both Chrome and Firefox browse to the same server they don't interfere with each other. QUIC innately has this functionality due to the way it implements encryption. Ideally the OS would allow a raw socket to register something akin to a BPF filter though as that would make it equally as efficient as UDP socket tracking even in the edge cases.
> Likewise NAT devices typically support UDP flows today due to their prevalence in games, but if you introduce a new transport protocol at the IP layer, they wouldn't be able to identify which flow (and therefore which NATed endpoint) the packet is destined for.
This is actually what I was referring to when I said:
> "IPv4 NAT & external firewalling has ossified protocols" which is a similar story of "just abstact up to avoid the issues"
We continue to make non choices to build up the stack rather than implement systems that are interchangeable.
Though I don't know what's wrong with UDP. 8 bytes of overhead for 1450 bytes IP payload is 0.5% bandwidth. Checksum overhead should be negligible.
That's expensive. Even if you avoid copying the packages by sharing memory between processes, there are still a lot of context switches...
1. Our design is complete, error-free and designed to stand the tests of time. It will be in common use, largely unchanged, in 40 years time. The TCP of the 2010s. There is widespread industry support. We want to move to the application layer to ease the initial roll-out.
2. Our design will need to change every few years, even we authors don't think it's finished. This is a Google-only project and most vendors are refusing to support it as they think it's badly designed crap. The ActiveX of the 2010s. We want to move to the application layer so we can force it through without anyone else's support.
Where are we on the spectrum between those two options? I don't know.
So no, it’s not the same.
Another issue they mention in the article is middleboxes, which basically will never be upgraded, and will never support new TCP features.
TCP Fast Open was standardized 8 years ago and is barely used. This is because updating TCP requires kernel updates, which just isn’t going to happen on most mobile devices.
Thus, moving the protocol to userspace makes a lot of sense.