Let me summarize the issue again. On RHEL 4U4 and below seems like locally sent multicast messages are received if listener is bound to the same interface as sender no matter if multicast route points to another interface. On RHEL 4U5 and above that is not the case so if sender and receiver are bound to the same interface but that is not the one with multicast route set through, receiver can't see anything. That is doubtfully sane. I think that exactly is causing the server bound to localhost to be unable to see its sent messages. So even if IP_MULTICAST_LOOP is just a hint, we have to set it anyway as long as we rely on that behavior and have to request it. I suggest we try that first to see if it will fix that particular issue. To make things work now, both servers have to bind their multicast sockets (only the multicast ones) to the same interface which mcast route goes through. For me that is sometimes inconvenient sometimes and error prone. I don't know how much sense does it make for JGroups itself to to bind or not bind multicast sockets to particular interface, but specifying interface is bad for JBoss AS manageability. Imagine server administrator is managing server interfaces and configures things to go through another one. That way the AS server will stop working properly. On the other hand if JBoss multicast socket is not bound to specific interface, it is highly unlikely that produce any issues. And even if it does in very specific cases, the user can specify interface manually. IMHO the safe choice is to not specify any interface for mcast socket and that will produce the "just work" feeling when one tries to run the test suite. I know some clients like to run the test suite locally and not having issues with it will make them more confident in JBoss AS quality. My feeling is that we'll have less issues with hudson runs as well ;) So two things we can do: 1. Ignore and disable noip run or 2. Try if IP_MULTICAST_LOOP fixes one of the issues *and* disable binding to specific interface for mcast sockets unless user requested that. P.S. anonymous wrote : | On dev90 when a server is bound to localhost? We already established that the problem does not exist on qa01. This is an important question -- if clustering tests work on dev90 with 4.2 but not with AS 5, there is something more we need to understand. | Difference between dev90 and qa01 if that one is RHEL 4U5 and the other 4U4. I will try clustering tests of AS 4.2 on dev90 with node0=localhost View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4102139#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...