why dns.gethotentry() method return addresslist as empty?

I use the following code to get the IP address:

var ip =   Dns.GetHostEntry(host);                   
 var ipaddress =ip.AddressList.FirstOrDefault(x => x.AddressFamily == AddressFamily.InterNetwork).ToString();

it return the hostname correctly. but the Addresslist is empty or does not return ipv4 address.

i can able to ping this hostname. and also it does not working, while i am giving local machine ipaddress.