All JBoss clustering services rely on JGroups.  To test if all clustered machines can see each other through JGroups, do the following steps:

• Take the log4j.properties file attached to this wiki page and put it in your <jboss install>/bin directory. (note: Why do this? The reason is not given by the author. Someone please correct this page)

Follow the instructions here to run 2 instances of ViewDemo with the configuration used in JBoss (e.g. clustering-service.xml).

You can also do this test on a single box. 

If both instances fail to see each other in the view then you need to fix your clustering problem at the JGroups level.  It could be something as simple as having multicast disabled on one or more machines.  If the test is sucessful then you know that the problem is (note: what problem is the author refereing to? How do you know if the test was successful?)with the configuration of some clustering service that runs on top of JGroups such as JBossCache or HttpSession Replication.