The current stable .Net Core websocket package does not support Linux, or pre-Win8.
#### Linux
Add the latest version of `System.Net.WebSockets.Client` from the .Net Core MyGet feed (`https://dotnet.myget.org/F/dotnet-core/api/v3/index.json`) to your project.
#### Windows 7 and earlier
There is currently no workaround, track the issue [here](https://github.com/dotnet/corefx/issues/9503).
### WebSockets (Win7 and earlier)
The .Net Core 1.1 does not support WebSockets on Win7 and earlier. Track the issue [here](https://github.com/dotnet/corefx/issues/9503).