Warning when increasing IHttpMaxRequestBodySizeFeature.MaxRequestBodySize despite all IIS limits increased

I have an ASP.NET Core 3.1 web API running on IIS on-prem (IIS 10 on Windows Server 2016). In an operation, I set IHttpMaxRequestBodySizeFeature.MaxRequestBodySize to 262144000. I have used the IIS Configuration Editor to

• modify ApplicationHost.config for my site by setting system.webServer/security/requestFiltering/requestLimits/maxAllowedContentLength to 4294967295
• modify ApplicationHost.config for my site by setting system.webServer/serverRuntime/maxRequestEntityAllowed to 4294967295
• modify Root Web.config for my site by setting system.web/httpRuntime/maxRequestLength to 2147483647

Those are the values I also see when I choose Web.config in the IIS Configuration Editor.

The site is behind another IIS site acting as a reverse proxy. I have made the same changes there.

I am able to upload files larger than the default ~30MB limit, but I consistently get the following warning whenever I set IHttpMaxRequestBodySizeFeature.MaxRequestBodySize:

Increasing the MaxRequestBodySize conflicts with the max value for IIS limit maxAllowedContentLength. HTTP requests that have a content-length greater than maxAllowedContentLength will still be rejected by IIS. You can disable the limit by either removing or setting the maxAllowedContentLength value to a higher limit.

I have even looked at the ASP.NET source code to verify that the warning only prints if you’re trying to set the limit higher than the IIS settings:

https://github.com/dotnet/aspnetcore/blob/214df1c8ef0cce27b04fcc43d7df48b29964dee1/src/Servers/IIS/IIS/src/Core/IISHttpServer.cs#L85-L88

https://github.com/dotnet/aspnetcore/blob/df712cc4a97d0bc8d573979008a5a2cc381f8117/src/Servers/IIS/IIS/src/Core/IISHttpContext.FeatureCollection.cs#L370-L373

Am I doing anything wrong, or is this a bug in ASP.NET Core?

Please let me know if I can provide more information.

If it’s relevant, I am publishing to IIS using Azure Pipelines. My repo does not contain a web.config, but for good measure I tried with the following web.config without luck:

<configuration>
  <system.web>
    <httpRuntime maxRequestLength="2147483647" />
  </system.web>
  <system.webServer>
    <security>
      <requestFiltering>
        <requestLimits maxAllowedContentLength="4294967295" />
      </requestFiltering>
    </security>
  </system.webServer>
</configuration>

[BrennanConroy]

Part of https://github.com/dotnet/aspnetcore/issues/22950 work

[BrennanConroy]

Fixed via https://github.com/dotnet/aspnetcore/pull/25096