AspNetCore.Docs/aspnetcore/includes/catchall.md

:::moniker range=">= aspnetcore-3.0 < aspnetcore-5.0"

[!WARNING] A catch-all parameter may match routes incorrectly due to a bug in routing. Apps impacted by this bug have the following characteristics:

• A catch-all route, for example, {**slug}"
• The catch-all route fails to match requests it should match.
• Removing other routes makes catch-all route start working.

See GitHub bugs 18677 and 16579 for example cases that hit this bug.

An opt-in fix for this bug is contained in .NET Core 3.1.301 SDK and later. The following code sets an internal switch that fixes this bug:

public static void Main(string[] args)
{
   AppContext.SetSwitch("Microsoft.AspNetCore.Routing.UseCorrectCatchAllBehavior", 
                         true);
   CreateHostBuilder(args).Build().Run();
}
// Remaining code removed for brevity.

:::moniker-end