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POJava Multicast sample program is unable to deliver packets within LAN (across hosts)
 

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  1. POJava Multicast sample program is unable to deliver packets within LAN (across hosts)
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    <p>I am learning and trying to understand how Multicast is implemented in Java. I had developed a small program following the example given at <a href="http://www.nmsl.cs.ucsb.edu/MulticastSocketsBook/#javaexamples" rel="nofollow noreferrer">http://www.nmsl.cs.ucsb.edu/MulticastSocketsBook/#javaexamples</a> and it did do multicast of datagram (UDP) packets to multiple clients on same host. </p> <p>However when I tried to run clients on different machines (within same LAN (i.e. my home WiFi) no packets got received at client end. I made sure that my router's firewall was disabled as well as all other machines had a port open.</p> <p>Thinking my program could have some error, I took the examples, compiled them and run server and client on different machines but same result (no packet delivery to different machines). I even tried running client on Ubuntu (within VirtualBox with Bridge Adapter) but no luck.</p> <p>After going through SO, I came across <a href="https://stackoverflow.com/questions/139909/java-multicast-time-to-live-is-always-0">Java Multicast Time To Live is always 0</a> explaining the problem with TTL header in Java multicast. So I applied the suggestion provided in that question's answer but still same problem. I tracked the packets with WireShark and verified that TTL had indeed value 5 (I set it to 5 to widen the probability !)</p> <p>I am not sure where I am doing wrong. I would really appreciate if you can point me into right direction.</p> <p>P.S. : I had used multicast addresses like 235.1.1.1 / 239.255.211.111 and port 4466 (this port I kept open in firewall of all machines for inbound + outbound n/w)</p>
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    1. COTell me whether your local host is `multi-homed` or not; i.e having more than one network interface. If you do, then you need to use the third constructor of `DatagramSocket` class where you need to supply local port and local binding IP address of your preferred network interface
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    2. COInteresting, I'm having the very same problems you are having in my Java project right this second! I'm not sure of a solution myself...
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    3. COIf you are in `multi-homed` setup and you are using `MulticastSocket` class, then use `setInterface(inetAddress)` to set the binding IP address of your preferred network interface
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