A merge is probably a sign that the during the initial discovery process when devl-03 started, it did not find the other servers during the timeout period. So it formed a cluster of one. Later it did find the other servers, and the two clusters merged. For a UDP config, the behavior of the discovery process is controlled via the PING protocol. See http://wiki.jboss.org/wiki/Wiki.jsp?page=JGroupsPING for more details. If you post the protocol stack portion of your cluster-service.xml file, I can have a look. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3993155#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...