[tyingq]

"Network providers" isn't really the issue. It's all the corporate and school networks that block UDP, or run broken spyware MITM boxes, etc. Chrome has to do a TCP vs UDP race to figure out if UDP connectivity to the internet is broken.

[kitteh]

In some cases it is the ISPs. I'll share an example:

Some broadband ISPs struggle with the fact that their customers get compromised and join botnets. Over the last few years UDP has become the ddos attack of choice. Broadband access networks struggle with how to mitigate this. Some try to block the command and control (C2) and some try to go the customer outreach angle. For example, notifying them that they have a compromised machine or putting them in a walled garden with a website that pops up telling them they've been impacted. The problem is that outreach is costly and not super effective. So they found another option: apply throttles on UDP. A few have done this and it's led to big problems because from a user experience QUIC works enough - and then falls apart.

Some of the access providers have changed the throttles to be less aggressive while others have resorted to being aggressive on the topic ("you should have made a new protocol and consulted with us!").