Background and Motivation

From #42840
A weird workaround is used for mask testing. Masking should be exposed as a direct concept for ip addresses.

Proposed API

namespace System.Net
{
    public class IPAddress
    {
+        public bool IsMask(IPAddress address, int maskLength);
    }
}

Usage Examples

var mask = IPAddress.Parse("192.168.0.0");
var address = IPAddress.Parse("192.168.1.1");
Assert.True(mask.IsMask(address, 16));

Alternative Designs

Expose a separated IPAddressMask type? Then mask length doesn't needed to be passed in every call.

Risks

Is storing masks violating the IPAddress type? If so, an IPAddressMask type should be appropriate.