copy V 8, moniker prep

Author: Rick-Anderson

aspnetcore/fundamentals/servers/kestrel/http3.md

@@ -83,4 +83,6 @@ HTTP/3 and QUIC have a number of benefits compared to HTTP/1.1 and HTTP/2:
 
 :::moniker-end
 
+[!INCLUDE[](~/fundamentals/servers/kestrel/includes/http3-8.md)]
+
 [!INCLUDE[](~/fundamentals/servers/kestrel/includes/http3-6-7.md)]

aspnetcore/fundamentals/servers/kestrel/includes/http-8.md

@@ -0,0 +1,69 @@
+:::moniker range="= aspnetcore-8.0"
+
+[HTTP/3](https://datatracker.ietf.org/doc/rfc9114/) is an approved standard and the third major version of HTTP. This article discusses the requirements for HTTP/3. HTTP/3 is fully supported in ASP.NET Core 7.0 and later.
+
+> [!IMPORTANT]
+> Apps configured to take advantage of HTTP/3 should be designed to also support HTTP/1.1 and HTTP/2.
+
+## HTTP/3 requirements
+
+HTTP/3 has different requirements depending on the operating system. If the platform that Kestrel is running on doesn't have all the requirements for HTTP/3, then it's disabled, and Kestrel will fall back to other HTTP protocols.
+
+### Windows
+
+* Windows 11 Build 22000 or later OR Windows Server 2022.
+* TLS 1.3 or later connection.
+
+### Linux
+
+* `libmsquic` package installed.
+
+`libmsquic` is published via Microsoft's official Linux package repository at `packages.microsoft.com`. To install this package:
+
+1. Add the `packages.microsoft.com` repository. See [Linux Software Repository for Microsoft Products](/windows-server/administration/linux-package-repository-for-microsoft-software) for instructions.
+2. Install the `libmsquic` package using the distro's package manager. For example, `apt install libmsquic=1.9*` on Ubuntu.
+
+**Note:** .NET 6 is only compatible with the 1.9.x versions of libmsquic. Libmsquic 2.x is not compatible due to breaking changes. Libmsquic receives updates to 1.9.x when needed to incorporate security fixes.  
+
+### macOS
+
+HTTP/3 isn't currently supported on macOS and may be available in a future release.
+
+## Getting started
+
+HTTP/3 is not enabled by default. Add configuration to `Program.cs` to enable HTTP/3.
+
+:::code language="csharp" source="samples/6.x/KestrelSample/Snippets/Program.cs" id="snippet_Http3" highlight="7-8":::
+
+The preceding code configures port 5001 to:
+
+* Use HTTP/3 alongside HTTP/1.1 and HTTP/2 by specifying `HttpProtocols.Http1AndHttp2AndHttp3`.
+* Enable HTTPS with `UseHttps`. HTTP/3 requires HTTPS.
+
+Because not all routers, firewalls, and proxies properly support HTTP/3, HTTP/3 should be configured together with HTTP/1.1 and HTTP/2. This can be done by specifying [`HttpProtocols.Http1AndHttp2AndHttp3`](xref:Microsoft.AspNetCore.Server.Kestrel.Core.HttpProtocols.Http1AndHttp2AndHttp3) as an endpoint's supported protocols.
+
+For more information, see <xref:fundamentals/servers/kestrel/endpoints>.
+
+## Alt-svc
+
+HTTP/3 is discovered as an upgrade from HTTP/1.1 or HTTP/2 via the [`alt-svc`](https://developer.mozilla.org/docs/Web/HTTP/Headers/Alt-Svc) header. That means the first request will normally use HTTP/1.1 or HTTP/2 before switching to HTTP/3. Kestrel automatically adds the `alt-svc` header if HTTP/3 is enabled.
+
+## Localhost testing
+
+* Browsers don't allow self-signed certificates on HTTP/3, such as the Kestrel development certificate.
+* `HttpClient` can be used for localhost/loopback testing in .NET 6 or later. Extra configuration is required when using `HttpClient` to make an HTTP/3 request:
+
+  * Set [`HttpRequestMessage.Version`](xref:System.Net.Http.HttpRequestMessage.Version) to 3.0, or
+  * Set [`HttpRequestMessage.VersionPolicy`](xref:System.Net.Http.HttpRequestMessage.VersionPolicy) to [`HttpVersionPolicy.RequestVersionOrHigher`](xref:System.Net.Http.HttpVersionPolicy.RequestVersionOrHigher).
+
+## HTTP/3 benefits
+
+HTTP/3 uses the same semantics as HTTP/1.1 and HTTP/2: the same request methods, status codes, and message fields apply to all versions. The differences are in the underlying transport. Both HTTP/1.1 and HTTP/2 use TCP as their transport. HTTP/3 uses a new transport technology developed alongside HTTP/3 called [QUIC](https://datatracker.ietf.org/doc/html/draft-ietf-quic-transport-34).
+
+HTTP/3 and QUIC have a number of benefits compared to HTTP/1.1 and HTTP/2:
+
+* Faster response time of the first request. QUIC and HTTP/3 negotiates the connection in fewer round-trips between the client and the server. The first request reaches the server faster.
+* Improved experience when there is connection packet loss. HTTP/2 multiplexes multiple requests via one TCP connection. Packet loss on the connection affects all requests. This problem is called "head-of-line blocking". Because QUIC provides native multiplexing, lost packets only impact the requests where data has been lost.
+* Supports transitioning between networks. This feature is useful for mobile devices where it is common to switch between WIFI and cellular networks as a mobile device changes location. Currently, HTTP/1.1 and HTTP/2 connections fail with an error when switching networks. An app or web browsers must retry any failed HTTP requests. HTTP/3 allows the app or web browser to seamlessly continue when a network changes. Kestrel doesn't support network transitions in .NET 8. It may be available in a future release.
+
+:::moniker-end