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From a backwards compatibility perspective, HTTP2->HTTP3 is really very similar to IPv4->IPv6. HTTP3 isn't really backwards compatible with HTTP2. The client ju
by scott00 5y ago
From a backwards compatibility perspective, HTTP2->HTTP3 is really very similar to IPv4->IPv6. HTTP3 isn't really backwards compatible with HTTP2. The client just establishes a lower version connection and then the server (which must implement both versions) adds a header to the response telling the client they can establish a HTTP3 connection if they want to. In IP land you get to skip the lower version initial connection because you've already figured it out from DNS, but other than that pretty much the same deal. In both cases both clients and servers that use a new version are dual-stacked because there are plenty of both clients and servers that only support the lower version.
- tsimionescu 5y agoYes, that was a poor example. Thinking about it more, the salient difference is that HTTP->HTTP2->HTTP3 is not a network-level problem to a similar extent (apart from clients and servers, you do have proxies and CDNs that need to support both, but these are far fewer actors, and it's much easier to switch CDN to one that supports HTTPx than it is to switch ISP as a server operator), that is the reason why adoption was much faster.