Thanks for the answer Brian. I have two machines with multiple interfaces. Clustering traffic is configured to go over bge2, and all other traffic (JNDI/RMI/JMS) is over bge1. If the two machines don't have IP connectivity over bge1 I get the following messages when a new member joins the cluster: 2006.07.21 12:51:20 WARN [org.jgroups.protocols.pbcast.NAKACK] [dino2:11800 (additional data: 17 bytes)] discarded message from non-member 10.10.10.10:11800 When the two machines can see each other over bge1 (as well as bge2), clustering works fine. In this case when a new member joins the cluster, I see traffic over 1098 at the beginning of the join. This is why I was suspecting RMI calls between the servers. Am I missing any obvious reasons why the first case doesn't work? What causes my second machine (10.10.10.10) to go from being a non-member, to being considered a member so that the first machine won't discard it's messages? Thanks Anne View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3960484#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...