First, if you are a support customer (you're using EAP), please open a case via the Customer Support Portal. There's no SLA via the forums. Otherwise, 1) Are you actually using UDP multicast? The ports shown in your logs seem more like what would be used by a TCP-based JGroups config. (Could be multicast though; depends on your config). 2) I need to understand what channels are using 192.168.11.102:1147 and 192.168.11.103:2600. Please find the logging that looks like this on the two nodes and post the area around it: ------------------------------------------------------- GMS: address is 192.168.11.102:1147 ------------------------------------------------------- or ------------------------------------------------------- GMS: address is 192.168.11.103:2600 ------------------------------------------------------- 3) The following will likely cause problems, although AFAIR not the NAKACK issue you are reporting: 15:50:45,995 INFO [DefaultPartition] All Members : 2 ([127.0.0.1:1099, 127.0.0.1:1099]) That tells me you have JBoss bound to 127.0.0.1 on both nodes. That would occur either by starting JBoss with -b 127.0.0.1 on both nodes, or by not setting -b and leaving the 127.0.0.1 default. The AS clustering code uses the bind address and JNDI port to form a unique cluster-wide id for each node. Works fine, except when you bind JBoss to 127.0.0.1 or 0.0.0.0 on more than one machine. If you *want* to use 127.0.0.1 or 0.0.0.0 as the -b value on more than one node, you should edit the server/all/deploy/cluster-service.xml's ClusterPartition mbean and either change ${jboss.bind.address} to something unique per server, like 192.168.11.102 or, explicitly configure a String "NodeName" attribute with a unique value per node: node1 Bottom line, you don't want duplicates in the "[DefaultPartition] All Members" logging. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4202979#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...