CloudFlare has supported it since 2023: https://blog.cloudflare.com/announcing-encrypted-client-hell... Firefox has had it enabled by default since version 119: https://support.mozilla.org/en-US/kb/faq-encrypted-client-he... so you can use it today.

Nginx mainline 1.29.x supports it. So once you get that and also the openssl version on your system, good to go. Likely too late for ubuntu 26.04, maybe in debian 14 next year, or of course rolling release distros / containers.

But, in a personal/single website server, ech does not really add privacy, adversaries can still observe the IP metadata and compare what's hosted there. The real benefits are on huge cloud hosting platforms.

Even if the browsers and servers don't support it, you could still enable it because the system is designed to be backward compatible.

TLS (the IETF Working Group not the protocol family named for them) have long experience with the fact that if you specify how B is compatible with A based on how you specified A and ship B what you did won't work because the middleboxes are all cost optimized and don't implement what you specified but instead whatever got the sale for the least investment.

So e.g. they'd work for exactly the way you use say TLS 1.0 in the Netscape 4 web browser which was popular when the middlebox was first marketed, or maybe they cope with exactly the features used in Safari but since Safari never sets this bit flag here they reject all connections with that flag.

What TLS learned is summarized as "have one joint and keep it well oiled" and they invented a technique to provide that oiling for one working joint in TLS, GREASE, Generate Random Extensions And Sustain Extensibility. The idea of GREASE is, if a popular client (say, the Chrome web browser) just insists on uttering random nonsense extensions then to survive in the world where that happens you must not freak out when there are extensions you do not understand. If your middlebox firmware freaks out when seeing this happen, your customers say "This middlebox I bought last week is broken, I want my money back" so you have to spend a few cents more to never do that.

But, since random nonsense is now OK, we can ship a new feature and the middleboxes won't freak out, so long as our feature looks similar enough to GREASE.

ECH achieves the same idea, when a participating client connects to a server which does not support ECH as far as it knows, it acts exactly the same as it would for ECH except, since it has neither a "real" name to hide nor a key to encrypt that name it fills the space where those would fit with random gibberish. As a server, you get this ECH extension you don't understand, and it is filled with random gibberish you also don't understand, this seems fine because you didn't understand any of it (or maybe you've switched it off, either way it's not relevant to you).

But for a middlebox this ensures they can't tell whether you're doing ECH. So, either they reject every client which could do ECH, which again that's how you get a bunch of angry customers, or, they accept such clients and so ECH works.

Just be aware any reasonable network will block this.

Russia blocked it for Cloudflare because the outer SNI was obviously just for ECH but that won't stop anyone from using generic or throw-away domains as the outer SNI. As for reasonable I don't quite follow. Only censorious countries or ISP's would do such a thing.

I can foresee Firewall vendors possibly adding a category for known outer-SNI domains used for ECH but at some point that list would be quite cumbersome and may run into the same problems as blocking CDN IP addresses.

Once upon a time, "reasonable networks" blocked ICMP, too.

They were wrong then, of course, and they're still wrong now.

Why is it "reasonable" to block it?

Procrastinators. FTFY.

Eventually these blocks won't be viable when big sites only support ECH. It's a stopgap solution that's delaying the inevitable death of SNI filtering.