HOW TO: Use SetSocketOption() with MulticastInterface OptionName in Visual Studio .NET

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This article was previously published under Q318911

SUMMARY

This article shows you how to use the Socket.SetSocketOption method with the socket option name parameter as MulticastInterface.

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The SetSocketOption Method

The SetSocketOption method of the Microsoft .NET Framework Socket class takes three parameters:

SocketOptionLevel
SocketOptionName
optionValue

The SocketOptionLevel defines option levels for the SetSocketOption and the GetSocketOption methods. The SocketOptionName defines different option names for the socket class. The optionValue parameter takes in the value for the particular option name.

When you use MulticastInterface as the value for the SocketOptionName enumeration, the optionValue expects an Index value of the particular Network Adapter or Interface. Note that there is currently no API in the .NET Framework to determine the index of a particular adapter. Therefore, the user must input the index value.

The following sample code shows you how to use SetSocketOption with the MulticastInterface socket option name. Type or paste the following code in the Main function of a new Microsoft Visual C# .NET console application:

int defaultPort = 5050;
string localName = Dns.GetHostName();

IPHostEntry hostEntry = new IPHostEntry();
hostEntry = Dns.GetHostByName(localName);
IPAddress localAddress = hostEntry.AddressList[0];

Socket mcastSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

// Bind the socket to default IP address and port.
mcastSocket.Bind(new IPEndPoint(localAddress,defaultPort));

Console.Write("\nSelect Adapter for outgoing Multicast packets (Adapter Index) :  ");
int index = int.Parse(Console.ReadLine());
int optionValue = (int)IPAddress.HostToNetworkOrder(index);

Console.Write("\nMulticast Address - To add membership : ");
IPAddress mcastAddress = IPAddress.Parse(Console.ReadLine());
		
Console.Write("\nPort number - Where Multicast members are listening : ");
int mcastPort = int.Parse(Console.ReadLine());
MulticastOption mcastOpt = new MulticastOption(mcastAddress,localAddress);
		
// Add membership to the group.
mcastSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, mcastOpt);
		
// Set the required interface for outgoing multicast packets.
mcastSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastInterface, optionValue);

// Send multicast packets.
string data = "This is a multicast packet";
mcastSocket.SendTo(ASCIIEncoding.ASCII.GetBytes(data), new IPEndPoint(mcastAddress,mcastPort));

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