The -u option will have multicast address, this is not a 'normal' IP address (often multicast is blocked by router/switches)
You might separate a cluster with this options:
-Djboss.partition.name=XXX -Djboss.partition.udpGroup=126.96.36.199 (same as -u) -Djboss.hapartition.mcast_port=39993
With the partition.name it is ensured that two nodes are in a separate cluster if the name is different even if the multicast address is the same (might be a performance issue).
If the mcast is blocked between two nodes you become only in trouble if you WANT to have a cluster.
Hi Wolf-Dieter Fink!
As you said, jgroup multicast ip is not a normal IP addr, so is it a resource of my system? Why you set the param: -Djboss.partition.udpGroup=188.8.131.52 ?? Why this IP: 184.108.40.206? This IP has to satisfy what conditions?
Multicast addresses are a special part of IP address space (220.127.116.11 to 18.104.22.168) see e.g. wikipedia http://en.wikipedia.org/wiki/Multicast_address
My address is only an example.
You have to ensure that all instance of JBoss that have to build a cluster use the same address/port and partition name.
Thank you for quick reply
So, if another machine know my jgroup ip and partition name, they would join my cluster illegally and do something wrong with my app!!!!
Can I config or restrict the number of IP join in my cluster?
If another machine know (configure the same) jgroup mcast address/port and partition name, it join the cluster legal, it works as designed.
You can't configure the same multicast and say 'don't allow 192.168.1.1 to join' !
So if you do not want to build a cluster use a different partition name and, to avoid unnecessary traffic, a different multicast address/port.
Thanks all !