Look at IP multicasting and IPv6 -------------------------------- Key: JGRP-638 URL: http://jira.jboss.com/jira/browse/JGRP-638 Project: JGroups Issue Type: Task Reporter: Bela Ban Assigned To: Bela Ban Priority: Minor Fix For: 2.7 Attachments: SimpleMulticast.java [Carlo DeWolf's email] Bug 1: Aha, in IPv6 mode the incorrect interface is chosen to send out packets. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4742177 So to actually get the right sender into the packet you must bind to the address. MultiSocket senderSocket = new MultiSocket(new InetSocketAddress(sendFrom, 0)); Loopback must always be false. I'm not sure why, but if falls apart if you set it to true. (Might be because of the above.) senderSocket.setLoopback(false); The receiving socket must be bound to INADDR_ANY (because of Windows): receiverSocket = new MultiSocket(port); Bug 2: The receiver socket must join with an interface, because else the packets sent from the sendSocket are immediately blocked by the interface (not a member of the group). receiverSocket.joinGroup(mcastaddr, netIf); // Note that port in mcastaddr is ignored. I think it's also possible to have the sendSocket join, but I'm done. The effect here was that as long as nobody joins on the default multicast interface, nobody receives packets. This would seldomly occur, because there is always someone who joins the default interface. I've attached by own multicast tester. Which works in every config except on Windows with the counterfeit, doubtful, dubious, equivocal, fake, false, fictitious, inaccurate, mythical, spurious, unauthenticated, ungenuine, unsubstantiated, untrue, unverified, wrong "MS TCP loopback" device. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://jira.jboss.com/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira