如何用SetSocketOption函数设置MulticastInterface属性

怎么用SetSocketOption函数设置MulticastInterface属性？
Socket   s   =   new   Socket(AddressFamily.InterNetwork,   SocketType.Dgram,   ProtocolType.Udp);
                        s.SetSocketOption(SocketOptionLevel.IP,   SocketOptionName.MulticastInterface,   ？？？);



[解决办法]
int optionValue = (int)IPAddress.HostToNetworkOrder(第几块网卡);
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastInterface, optionValue );