This is a copy of a post I made in the C# forum. It really is a networking question. Please help me if you can.

I have a program that sends out UDP traffic via csharp. The code works in the local LAN. We even got it working to other VLANs through ip pim sparse-dense-mode on our Cisco 6504 switch. The problem is that we want this to run to a remote location outside of our LAN. We have a T1 connection to another site. We can ping and do file transfers with the remote machines. But the remote machines do not "hear" the multicast messages. What settings need to be set so that the remote site can get this multicast traffic? Many thanks in advance.


The Server:

private IPEndPoint iepSend = null;
private IPEndPoint iepSend2 = null;
private Socket sendSocket = null;
sendSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
iepSend = new IPEndPoint(IPAddress.Any, 4203);
iepSend2 = new IPEndPoint(IPAddress.Parse(""), 4203);
sendSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(IPAddress.Parse("")));
sendSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 50);
byte[] bytes = UnicodeEncoding.ASCII.GetBytes("hello world");
sendSocket.SendTo(bytes, iepSend2);

The Client

UdpClient clientListener = new UdpClient(4203);            
IPEndPoint iep = new IPEndPoint(IPAddress.Any, 0);
byte[] bytes = clientListener.Receive(ref iep);
string s = UnicodeEncoding.ASCII.GetString(bytes);

From what I gathered from your post, you are trying to push multicast over the internet. This will not work as most ISP's block multicast from the end user.

What I would suggest is this:

Depending on what type of hardware you have connecting these two sites, a VPN is what you need. The problem with this is, a regular IPSec VPN will not move multicast, so must start with a GRE tunnel and then encrypt it in an IPSec tunnel. If you are working with Cisco switches, I would assume you have access to Cisco routers. A router in the 1800 or 2800 series would work well, or even as low as the 2600 series (depending on how much data you are planning on moving).

The below link is a good example (in pdf format) from Cisco on setting up the above mentioned config:

hope this helps

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