I don't know much about NLB. But from looking at http://technet2.microsoft.com/WindowsServer/f/?en/library/1611cae3-5865-4... I get the feeling you should have multiple adapters on your servers, with NLB working on one and your JBoss intra-cluster traffic on the other. Also note that you can run JBoss clustering without using UDP multicast; a sample protocol stack is shown here: http://wiki.jboss.org/wiki/Wiki.jsp?page=JGroupsStackTCP . The standard clustering service deployment descriptors also include commented-out example TCP configs. I have no idea whether that would work any better with NLB though. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4025293#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...