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[GW] Respond 502 Bad Gateway when receiving HTTP_1_1_REQUIRED #17423

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Oct 11, 2024
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[GW] Respond 502 Bad Gateway when receiving HTTP_1_1_REQUIRED #17423

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[ZT] Gateway will respond 502 Bad Gateway when receiving HTTP_1_1_REQ…
kyouheicf Oct 9, 2024
8dffc89
Apply PCX style guide
maxvp Oct 10, 2024
a74457b
Fix with the intended context
kyouheicf Oct 11, 2024
2ba77d7
Fix grammar
maxvp Oct 11, 2024
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6 changes: 6 additions & 0 deletions src/content/docs/cloudflare-one/faq/troubleshooting.mdx
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Expand Up @@ -174,3 +174,9 @@ To enable software rasterization:
By default, the WARP client blocks outgoing SMTP traffic on port `25` to prevent users from abusing our service to send spam. Modern email service providers use port `587` or `465` to encrypt emails over a TLS/SSL connection. For more information, refer to [What SMTP port should be used?](https://www.cloudflare.com/learning/email-security/smtp-port-25-587/).

If you need to unblock port `25`, contact your account team.

## I see `502 Bad Gateway` when browsing to a website.

This issue can occur when communicating with an origin that partially supports HTTP/2. In these scenarios, the connection from Gateway to the website starts using HTTP/2 but requests a downgrade to HTTP/1.1 for some requests. For example, servers such as [Microsoft Internet Information Services (IIS)](https://learn.microsoft.com/iis/get-started/whats-new-in-iis-10/http2-on-iis#when-is-http2-not-supported) do not support authentication over HTTP/2. When errors occur, the website may send back a `RST_STREAM` frame with the error code `HTTP_1_1_REQUIRED`, which indicates that the browser should retry the request over HTTP/1.1. Gateway translates any received upstream `RST_STREAM` frames to a pseudo socket close, so this appears as a `502 Bad Gateway` exception page. The browser will not indicate why it failed.

Gateway does not support this downgrade mechanism. When receiving the `HTTP_1_1_REQUIRED` error code, Gateway will not reissue requests over HTTP/1.1. To make the connection from Gateway to the website successfully, you will need to disable HTTP/2 at the origin.
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