Multicast getting garbage message on Linux but not on Solaris!?

 tak <>
Thu, 13 Sep 2007 06:35:09 -0700

Heres the scenario...

We have an java application running on Linux, which basically listens
to multiple multicast IPs, process them, and other things. Issue comes
in when, say Message#1 is being published on IP#1, and Message#2 is
being published from IP#2... so on... When the application starts, we
would get Message#2 on BOTH IP#1, and IP#2!!!! And If the application
is listening to 3 multicast IPs, EACH message is coming into ALL 3
channels all the time. This is bizarre, and it is causing the data to
be X (X is the number of IP we are listening) as much.

And when we bring this to Solaris - it works perfectly fine. No
duplication. Each message only goes to which ever channel it is
suppose to.

So, we wrote a very little program, which basically uses java API to
connect to the multicast socket, and start listening, and we are ABLE
to duplicate this issue.

Here are some notes after further testing.

1. It only happens on Linux
2. It should NOT be the routing on the box - b/c we have a C++
application, that listens to the same multicast IPs, and they are
working fine.
3. We create a C++ multicast listener that print out the sequence
numbers (The first byte of the each packet is the sequence number for
us), and it does NOT have duplicate messages.
4. When we create a java multicast Listener that print out sequence
numbers, and it DOES have duplicate messages (if i listens to 2 IPs
5. This duplicate message ONLY happens, when there are multiple feeds
are being publisher on to the same port (i.e. feedHandler#1 is
publishing to,, and feedHandler#2 is publishing to, then our java application, would get messages as
if they came in from both channels)
6. Say NO one is publishing to, if we start the
little java mcast app, it would receive some data (no idea where it is
coming from) as long as some other feedhandlers are using that port,
18900 (even tho with diff IP). Meaning, say FH#1 is publishing to,, and If i start listening onto
(a complete diff IP), I would get data!!!

I have spent a few days on why this is happening already with no
luck.. However, with elimination, I dont think it is the routing on
the box, as it works fine for the C++ application that listens to same

I do not think it is the application, b/c with the small java mcast
app, it is very very simple, and is mostly taken directly from the sun
tutorial (Will post code following this message), and it works fine
for Solaris.

Here is the code for the little small mcast app that we used to
test... (Note: Beginning of each byte from each packet is our sequence
number - our feed handlers put them there before sending it out) This
app has 2 classes.

--- ----

import java.util.Properties;

public class TestingProgram extends Thread{
        private static String option =
        private static final int RECEIVE_BUFFER_SIZE = 500 * 1024;

        public TestingProgram(String str){
        String ips[] = str.split(";");
        int i = 0;
        for (i =0; i < ips.length; i++){
                String temp[] = ips[i].split(":");
                System.out.println("Adding FeedDataService Source for
" + temp[0] + ":" + temp[1]);
                TestingClass test = new TestingClass(i+1); // we will
create X TestingClass based on X IPs.
                test.connect(temp[0], Integer.parseInt(temp[1]));
        System.out.println(i + " feed data service initialized");
        } catch (Exception e){ }

        public static void main(String[] args) {
         private static String str=
                new TestingProgram(str);
                System.out.println("Main initialized");


----- -----


public class TestingClass extends Thread{

    private int PACKET_BUFFER_SIZE = 4096;
    private int RECEIVE_BUFFER_SIZE = 4096;
    private DatagramPacket datagramPacket;
    private DataInputStream dataInputStream;
    private MulticastSocket socket;
    private String host;
    private int port;
    private int num;

        public TestingClass(int i){
                num =i;
                byte[] packetBuffer = new byte[PACKET_BUFFER_SIZE];
                datagramPacket = new DatagramPacket(packetBuffer,
                dataInputStream = new DataInputStream(new
                } catch (Exception e){
                        System.out.println("Exception at TestingClass
" + e);

        public void connect(String host, int port){
       = host;
                InetAddress groupAddress =
                socket = new MulticastSocket(port);
                System.out.println("Group joined for " + host + ":" +
                System.out.println(host + " Thread started");
                } catch (Exception e){
                        System.out.println("Exception at connect "
+ e);

    public void run(){
        int count=0;
        short seqNum = 0;
        System.out.println(host + " going into receive() now");
        while (true) {
            try {
                seqNum = dataInputStream.readShort();
                System.out.println("Listener #" +num + " got packet #"
+ count + " from host: " + host + " dgram.getSocketAddress(): " +
datagramPacket.getSocketAddress() + " packet length: " +
datagramPacket.getLength() + " seqNum: " + seqNum);
            } catch (Exception exception) {
                throw new RuntimeException("Failed to receive

Can someone take a look, and see what is wrong? Is there something
special that needs to be done for Linux with listening to multiple
multicast ips??


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