UdpClient::JoinMulticastGroup Method (IPAddress^)

 
System_CAPS_noteNote

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Adds a UdpClient to a multicast group.

Namespace:   System.Net.Sockets
Assembly:  System (in System.dll)

public:
void JoinMulticastGroup(
	IPAddress^ multicastAddr
)

Parameters

multicastAddr
Type: System.Net::IPAddress^

The multicast IPAddress of the group you want to join.

Exception Condition
ObjectDisposedException

The underlying Socket has been closed.

SocketException

An error occurred when accessing the socket. See the Remarks section for more information.

ArgumentException

The IP address is not compatible with the AddressFamily value that defines the addressing scheme of the socket.

The JoinMulticastGroup method subscribes the UdpClient to a multicast group using the specified IPAddress. After calling the JoinMulticastGroup method, the underlying Socket sends an Internet Group Management Protocol (IGMP) packet to the router requesting membership to the multicast group. The multicast address range is 224.0.0.0 to 239.255.255.255. If you specify an address outside this range or if the router to which the request is made is not multicast enabled, UdpClient will throw a SocketException. If you receive a SocketException, use SocketException::ErrorCode to obtain the specific error code. Once you have obtained this code, you can refer to the Windows Sockets version 2 API error code documentation in MSDN for a detailed description of the error. Once the UdpClient is listed with the router as a member of the multicast group, it will be able to receive multicasted datagrams sent to the specified IPAddress.

System_CAPS_noteNote

You must create the UdpClient using the multicast port number; otherwise, you will not be able to receive multicasted datagrams. Do not call the Connect method prior to calling the JoinMulticastGroup method, or the Receive method will not work. You do not need to belong to a multicast group to send datagrams to a multicast IP address.

Before joining a multicast group, make sure the socket is bound to the port or endpoint. You do that by calling one of the constructors that accept a port or an endpoint as a parameter.

To stop receiving multicasted datagrams, call the DropMulticastGroup method and provide the IPAddress of the group from which you would like to withdraw.

System_CAPS_noteNote

In the IPv6 case, there are several multicast address ranges you can choose from. Please, refer to the IETF RFC 2375.

System_CAPS_noteNote

You cannot call JoinMulticastGroup on a UdpClient constructed without a specific local port (that is, using the UdpClient() or UdpClient(AddressFamily) constructor).

The following code example demonstrates how to join a multicast group by providing a multicast address.

#using <System.dll>

using namespace System;
using namespace System::Net;
using namespace System::Net::Sockets;
using namespace System::Text;
using namespace System::IO;
using namespace System::Threading;

// The following Receive class is used by both the ClientOriginator and
// the ClientTarget class to receive data from one another..
public ref class Receive
{
public:

   // The following static method performs the actual data
   // exchange. In particular, it performs the following tasks:
   // 1)Establishes a communication endpoint.
   // 2)Receive data through this end point on behalf of the
   // caller.
   // 3) Returns the received data in ASCII format.
   static String^ ReceiveUntilStop( UdpClient^ c )
   {
      String^ strData = "";
      String^ Ret = "";
      ASCIIEncoding^ ASCII = gcnew ASCIIEncoding;

      // Establish the communication endpoint.
      IPEndPoint^ endpoint = gcnew IPEndPoint( IPAddress::IPv6Any,50 );
      while (  !strData->Equals( "Over" ) )
      {
         array<Byte>^data = c->Receive( endpoint );
         strData = ASCII->GetString( data );
         Ret = String::Concat( Ret, strData, "\n" );
      }

      return Ret;
   }

};


// The following Send class is used by both the ClientOriginator and
// ClientTarget classes to send data to one another.
public ref class Send
{
private:
   static array<Char>^greetings = {'H','e','l','l','o',' ','T','a','r','g','e','t','->'};
   static array<Char>^nice = {'H','a','v','e',' ','a',' ','n','i','c','e',' ','d','a','y','->'};
   static array<Char>^eom = {'O','v','e','r'};
   static array<Char>^tGreetings = {'H','e','l','l','o',' ','O','r','i','g','i','n','a','t','o','r','!'};
   static array<Char>^tNice = {'Y','o','u',' ','t','o','o','->'};

public:

   // The following static method sends data to the ClientTarget on
   // behalf of the ClientOriginator.
   static void OriginatorSendData( UdpClient^ c, IPEndPoint^ ep )
   {
      Console::WriteLine( gcnew String( greetings ) );
      c->Send( GetByteArray( greetings ), greetings->Length, ep );
      Thread::Sleep( 1000 );
      Console::WriteLine( gcnew String( nice ) );
      c->Send( GetByteArray( nice ), nice->Length, ep );
      Thread::Sleep( 1000 );
      Console::WriteLine( gcnew String( eom ) );
      c->Send( GetByteArray( eom ), eom->Length, ep );
   }


   // The following static method sends data to the ClientOriginator on
   // behalf of the ClientTarget.
   static void TargetSendData( UdpClient^ c, IPEndPoint^ ep )
   {
      Console::WriteLine( gcnew String( tGreetings ) );
      c->Send( GetByteArray( tGreetings ), tGreetings->Length, ep );
      Thread::Sleep( 1000 );
      Console::WriteLine( gcnew String( tNice ) );
      c->Send( GetByteArray( tNice ), tNice->Length, ep );
      Thread::Sleep( 1000 );
      Console::WriteLine( gcnew String( eom ) );
      c->Send( GetByteArray( eom ), eom->Length, ep );
   }


private:

   // Internal utility
   static array<Byte>^ GetByteArray( array<Char>^ChArray )
   {
      array<Byte>^Ret = gcnew array<Byte>(ChArray->Length);
      for ( int i = 0; i < ChArray->Length; i++ )
         Ret[ i ] = (Byte)ChArray[ i ];
      return Ret;
   }

};


// The ClientTarget class is the receiver of the ClientOriginator
// messages. The StartMulticastConversation method contains the
// logic for exchanging data between the ClientTarget and its
// counterpart ClientOriginator in a multicast operation.
public ref class ClientTarget
{
private:
   static UdpClient^ m_ClientTarget;
   static IPAddress^ m_GrpAddr;

public:

   // The following StartMulticastConversation method connects the UDP
   // ClientTarget with the ClientOriginator.
   // It performs the following main tasks:
   // 1)Creates a UDP client to receive data on a specific port and using
   // IPv6 addresses. The port is the same one used by the ClientOriginator
   // to define its communication endpoint.
   // 2)Joins or creates a multicast group at the specified address.
   // 3)Defines the endpoint port to send data to the ClientOriginator.
   // 4)Receives data from the ClientOriginator until the end of the
   // communication.
   // 5)Sends data to the ClientOriginator.
   // Note this method is the counterpart of the
   // ClientOriginator::ConnectOriginatorAndTarget().
   static void StartMulticastConversation()
   {
      String^ Ret;

      // Bind and listen on port 1000. Specify the IPv6 address family type.
      m_ClientTarget = gcnew UdpClient( 1000,AddressFamily::InterNetworkV6 );

      // Join or create a multicast group
      m_GrpAddr = IPAddress::Parse( "FF01::1" );

      // Use the overloaded JoinMulticastGroup method.
      // Refer to the ClientOriginator method to see how to use the other
      // methods.
      m_ClientTarget->JoinMulticastGroup( m_GrpAddr );

      // Define the endpoint data port. Note that this port number
      // must match the ClientOriginator UDP port number which is the
      // port on which the ClientOriginator is receiving data.
      IPEndPoint^ ClientOriginatordest = gcnew IPEndPoint( m_GrpAddr,2000 );

      // Receive data from the ClientOriginator.
      Ret = Receive::ReceiveUntilStop( m_ClientTarget );
      Console::WriteLine( "\nThe ClientTarget received: \n\n {0}\n", Ret );

      // Done receiving, now respond to the ClientOriginator.
      // Wait to make sure the ClientOriginator is ready to receive.
      Thread::Sleep( 2000 );
      Console::WriteLine( "\nThe ClientTarget sent:\n" );
      Send::TargetSendData( m_ClientTarget, ClientOriginatordest );

      // Exit the multicast conversation.
      m_ClientTarget->DropMulticastGroup( m_GrpAddr );
   }

};


// The following ClientOriginator class starts the multicast conversation
// with the ClientTarget class..
// It performs the following main tasks:
// 1)Creates a socket and binds it to the port on which to communicate.
// 2)Specifies that the connection must use an IPv6 address.
// 3)Joins or create a multicast group.
//   Note that the multicast address ranges to use are specified
//   in the RFC#2375.
// 4)Defines the endpoint to send the data to and starts the
// client target (ClientTarget) thread.
public ref class ClientOriginator
{
private:
   static UdpClient^ clientOriginator;
   static IPAddress^ m_GrpAddr;
   static IPEndPoint^ m_ClientTargetdest;
   static Thread^ m_t;

public:

   // The ConnectOriginatorAndTarget method connects the
   // ClientOriginator with the ClientTarget.
   // It performs the following main tasks:
   // 1)Creates a UDP client to receive data on a specific port
   //   using IPv6 addresses.
   // 2)Joins or create a multicast group at the specified address.
   // 3)Defines the endpoint port to send data to on the ClientTarget.
   // 4)Starts the ClientTarget thread that also creates the ClientTarget Object*.
   // Note this method is the counterpart of the
   // ClientTarget::StartMulticastConversation().
   static bool ConnectOriginatorAndTarget()
   {
      try
      {

         // Bind and listen on port 2000. This constructor creates a socket
         // and binds it to the port on which to receive data. The family
         // parameter specifies that this connection uses an IPv6 address.
         clientOriginator = gcnew UdpClient( 2000,AddressFamily::InterNetworkV6 );

         // Join or create a multicast group. The multicast address ranges
         // to use are specified in RFC#2375. You are free to use
         // different addresses.
         // Transform the String* address into the internal format.
         m_GrpAddr = IPAddress::Parse( "FF01::1" );

         // Display the multicast address used.
         Console::WriteLine( "Multicast Address: [ {0}]", m_GrpAddr );

         // Exercise the use of the IPv6MulticastOption.
         Console::WriteLine( "Instantiate IPv6MulticastOption(IPAddress)" );

         // Instantiate IPv6MulticastOption using one of the
         // overloaded constructors.
         IPv6MulticastOption^ ipv6MulticastOption = gcnew IPv6MulticastOption( m_GrpAddr );

         // Store the IPAdress multicast options.
         IPAddress^ group = ipv6MulticastOption->Group;
         __int64 interfaceIndex = ipv6MulticastOption->InterfaceIndex;

         // Display IPv6MulticastOption properties.
         Console::WriteLine( "IPv6MulticastOption::Group: [ {0}]", group );
         Console::WriteLine( "IPv6MulticastOption::InterfaceIndex: [ {0}]", interfaceIndex );

         // Instantiate IPv6MulticastOption using another
         // overloaded constructor.
         IPv6MulticastOption^ ipv6MulticastOption2 = gcnew IPv6MulticastOption( group,interfaceIndex );

         // Store the IPAdress multicast options.
         group = ipv6MulticastOption2->Group;
         interfaceIndex = ipv6MulticastOption2->InterfaceIndex;

         // Display the IPv6MulticastOption2 properties.
         Console::WriteLine( "IPv6MulticastOption::Group: [ {0} ]", group );
         Console::WriteLine( "IPv6MulticastOption::InterfaceIndex: [ {0} ]", interfaceIndex );

         // Join the specified multicast group using one of the
         // JoinMulticastGroup overloaded methods.
         clientOriginator->JoinMulticastGroup( (int)interfaceIndex, group );

         // Define the endpoint data port. Note that this port number
         // must match the ClientTarget UDP port number which is the
         // port on which the ClientTarget is receiving data.
         m_ClientTargetdest = gcnew IPEndPoint( m_GrpAddr,1000 );

         // Start the ClientTarget thread so it is ready to receive.
         m_t = gcnew Thread( gcnew ThreadStart( ClientTarget::StartMulticastConversation ) );
         m_t->Start();

         // Make sure that the thread has started.
         Thread::Sleep( 2000 );
         return true;
      }
      catch ( Exception^ e ) 
      {
         Console::WriteLine( "[ClientOriginator::ConnectClients] Exception: {0}", e );
         return false;
      }

   }


   // The SendAndReceive performs the data exchange
   // between the ClientOriginator and the ClientTarget classes.
   static String^ SendAndReceive()
   {
      String^ Ret = "";

      // Send data to ClientTarget.
      Console::WriteLine( "\nThe ClientOriginator sent:\n" );
      Send::OriginatorSendData( clientOriginator, m_ClientTargetdest );

      // Receive data from ClientTarget
      Ret = Receive::ReceiveUntilStop( clientOriginator );

      // Stop the ClientTarget thread
      m_t->Abort();

      // Abandon the multicast group.
      clientOriginator->DropMulticastGroup( m_GrpAddr );

      return Ret;
   }

};


//This is the console application entry point.
int main()
{

   // Join the multicast group.
   if ( ClientOriginator::ConnectOriginatorAndTarget() )
   {

      // Perform a multicast conversation with the ClientTarget.
      String^ Ret = ClientOriginator::SendAndReceive();
      Console::WriteLine( "\nThe ClientOriginator received: \n\n {0}", Ret );
   }
   else
   {
      Console::WriteLine( "Unable to Join the multicast group" );
   }
}

.NET Framework
Available since 1.1
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