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UdpClient.JoinMulticastGroup Method (IPAddress, IPAddress)

Adds a UdpClient to a multicast group.

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

public void JoinMulticastGroup(
	IPAddress multicastAddr,
	IPAddress localAddress


Type: System.Net.IPAddress
The multicast IPAddress of the group you want to join.
Type: System.Net.IPAddress
The local IPAddress.


The underlying Socket has been closed.


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

Before you join a multicast group, be sure that the socket is bound to the port or endpoint. You can do this by calling one of the constructors that accepts a port or an endpoint as parameter.


There are several multicast address ranges to choose from. You can find them in the IETF RFC 2375.


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 shows the use of the JoinMulticastGroup method.

// Subscribe to a multicast group.
public static void DoJoinMulticastGroup(UdpClient u, string mcast)
    IPAddress[] multicastAddress = Dns.GetHostAddresses(mcast);

    Console.WriteLine("Joined multicast Address {0}",

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.