.NET Core 2 Sockets Improvements

In .NET Core, a new type System.Net.Http.SocketsHttpHandler, and a rewritten System.Net.Http.HttpMessageHandler are added. They form the basis of higher-level networking APIs.

  • System.Net.Http.SocketsHttpHandler is the basis of the HttpClient implementation.
  • In previous versions of .NET Core, higher-level APIs were based on native networking implementations.

The sockets implementation introduced in .NET Core 2.1 has a number of advantages:

  • A significant performance improvement when compared with the previous implementation.
  • The elimination of platform dependencies, which simplifies deployment and servicing.
  • Consistent behavior across all .NET Core platforms.

If this change is undesirable, you can configure your application to use the older System.Net.Http.HttpClientHandler class instead in a number of ways:

By calling the AppContext.SetSwitch method as follows:

AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);

By defining the System.Net.Http.UseSocketsHttpHandler switch in the .netcore.runtimeconfig.json configuration file:

"runtimeOptions": {
  "configProperties": {
      "System.Net.Http.UseSocketsHttpHandler": false

By defining an environment variable named DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER and setting it to either false or 0.


On Windows, you can also choose to use System.Net.Http.WinHttpHandler, which relies on a native implementation, or the SocketsHttpHandler class by passing an instance of the class to the HttpClient constructor.

Linux and macOS

  • On Linux and macOS, you can only configure HttpClient on a per-process basis.
  • On Linux, you need to deploy libcurl if you want to use the old HttpClient implementation.