Setting network interface and ttl for MulticastSocket

Question

Hello
I've tried to set the network interface and the TTL for a MulticastSocket, but it has no effect. For testing I set the TTL to '4' and the network interface to 'lo' (localhost), but everybody in the local area network get my message with TTL=1...
I use Fedora Core 5 (Linux), with no settings in the iptables.
Here is the code I used:
private String networkInterface="lo";
private String address="239.192.0.5";
private int port=54321;
private int mcastTtl=4;
public void send(){
InputStream input=getContextClassLoader().getResourceAsStream("something.xml");
byte[] buffer = new byte[1480];
int length = input.read(buffer,0, 1480);
inetAddress = InetAddress.getByName(address);
nInterface=NetworkInterface.getByName(networkInterface);
MulticastSocket socket = new MulticastSocket(port);
socket.joinGroup(inetAddress);
DatagramPacket packet = new DatagramPacket(buffer, length,
inetAddress, port);
socket.setTimeToLive(mcastTtl);
socket.setNetworkInterface(nInterface);
socket.send(packet);
socket.leaveGroup(inetAddress);
For simplicity I took the Error handling off here, but certainly I have it in my code. No errors, no problems, everybody get the correct message... But not with the settings I made.
Any tips?
Thanks:
Bence

Answer 1

I'm seeing the exact same thing. It's as if setNetworkInterface() doesn't actually do anything at all.
java version "1.5.0_09"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_09-b03)
Java HotSpot(TM) Server VM (build 1.5.0_09-b03, mixed mode)
OS: Linux kernel 2.6.14.3, CentOS 4.2
Code example (parts removed for clarity) follows. This code works perfectly when I allow it to attach to the default (eth0) interface. When I try to change the interface it binds to, all packets are still multicast to eth0 ONLY! I see nothing on lo or eth1.
Properties props = System.getDefaultProperties();
props.setProperty("java.net.preferIPv4Stack","true");
MulticastSocket mcs = new MulticastSocket(localPort);
mcs.setNetworkInterface(NetworkInterface.getByName("eth1"));
InetAddress group = InetAddress.getByName("230.1.1.1");
String payload = "This is my payload";
DatagramPacket dgram = new DatagramPacket(payload.getBytes(),
payload.length(),
group, groupPort);
mcs.send(dgram);