I'm guessing a network problem unrelated to multicast. My interpretation is that your SLSB is deployed on both nodes. For an SLSB, there is no intracluster traffic related to it after it deploys. If it's deployed on all nodes, there is no intra-cluster HA-JNDI traffic related to clients looking it up. Those two facts eliminate a whole range of areas to explore. Configure a jndi.properties on your client where you specify the host names of your servers; i.e. don't use HA-JNDI auto discovery java.naming.provider.url=host1:1100,host2:1100 If you do that, there is no multicast at all involved in what you are doing. You're basically downloading a JNDI stub, doing lookups and making invocations that cause no intra-cluster activity on the server side. Not much difference from a non-clustered scenario. Only difference is the JNDI and EJB proxies will spread the calls over both nodes rather than targeting only one. If you find you have problems in this scenario, I would look for problems on each node standalone. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4127044#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...