[lxgr]

IPv6 doesn't provide a length header, so that's already 2 bytes arguably necessary for all protocols layered on top of that.

Source and destination port just seem like a reasonable baseline for alternate protocols, that's 4 more – leaving just the checksum. (If you're really desperate for space and have integrity provided by your protocol, you can even cram two more bytes in there!)

Sure, it would be conceptually nice to be able to skip UDP, but I think in terms of performance it absolutely does not matter.

[IgorPartola]

QUIC doesn’t use the UDP length header to designate message length, does it?

But my point isn’t even about performance. It is about the fact that NAT and IPv4 address exhaustion and bad firewall practices have killed any innovation of level 4 protocols. Imagine if instead of TCP, SCTP had won the protocol wars in 1980-1990s. Or even better if we had realized that we were going to run out of IPv4 addresses much earlier when the cost of switching was smaller. It would have been so much better to have firewalls that don’t filter anything but protocols 6 and 17. We could have had the opportunity to experiment with different types of transports, baked encryption in at a lower level, etc.

Basically where we are is that we have 6 and 8 dot LEGO bricks to play with and are told that we can build anything with those but aren’t allowed to play with any other shapes.

[lxgr]

> QUIC doesn’t use the UDP length header to designate message length, does it?

Does it not? Not sure if it's really mandatory, but I believe one rationale for IPv6 getting rid of both its checksum and length fields was that both TCP and UDP duplicate both fields.

Given that QUIC doesn't have its own length field, I would imagine it relies on that of UDP, at least in situations where the lower layer does not provide reliable framing?

> Imagine if instead of TCP, SCTP had won the protocol wars in 1980-1990s. [...] We could have had the opportunity to experiment with different types of transports, baked encryption in at a lower level, etc.

Would we? Instead of TCP, SCTP would have become ossified in the stack all other things being equal (in particular the need for something like NAT due to IPv6 exhaustion), no?