I want to use the class "IPAddress" in System.Net on wp8.1. I also write the code "using System.Net;". But it still can not find this class. The code is as follows:

```
  using System.Net;
  ................

  IPAddress ip = new IPAddress("192.168.1.2");

```

Visual Studio 2013 tell me that "Generate class for 'IPAddress'". 

Looking forward for anyone's reply!