Here, if a nameserver [::]:53 is used, it will be converted into :::53, which makes throw System.Net.Sockets.SocketException (10049): AddressNotAvailable

It may be fixed by

public override string ToString()
{
    return AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6 ? $"[{Address}]:{Port}" : $"{Address}:{Port}";
}