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HTTP/2 Compatibility with old Browsers and Servers

This post is a part 1 of HTTP/2 Complete Tutorial post series.

One of the biggest question that comes in is how is old browsers going to deal with HTTP/2 web servers and vice-versa.

HTTP/2 uses an Upgrade and Discovery method to find if a server supports HTTP/2 or not.

An HTTP/2 client never makes a HTTP/2 request by default. It always makes an HTTP/1.1 request with Upgrade: HTTP/2.0 header. If the web server is HTTP/2 capable then the server responds with HTTP/1.1 101 Switching Protocols status. But if the server is not capable of HTTP/2 then it simply returns an HTTP/1.1 response.

Clients usually remember whether the server supported HTTP/2 or not. And then the next time it makes an HTTP request it tries to make an HTTP/2 request directly instead of relying on upgrade round trip again.

Narayan Prusty
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Comments: 1
  1. Vic
    5 years ago

    You mention the client can remember if the server supports HTTP/2; where is this information stored in the browser? Is it by domain or IP address or something else?

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Narayan Prusty

I am a software engineer specialising in Blockchain, DevOps and Go/JavaScript. This is my personal blog where I write about things that I learn and feel interesting to share.

7 years ago 1 Comment Web Development
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