Within JBoss AS, there are a number of services that independently create JGroups channels -- 3 different JBoss Cache services (used for HttpSession replication, EJB3 SFSB replication and EJB3 entity replication) along with the general purpose clustering service called HAPartition that underlies most other JBossHA services.

It is critical that these channels only communicate with their intended peers; not with the channels used by other services and not with channels for the same service opened on machines not meant to be part of the group. Nodes improperly communicating with each other is one of the most common issues users have with JBoss AS clustering.

Whom a JGroups channel will communicate with is defined by its group name, multicast address, and multicast port, so isolating JGroups channels comes down to ensuring different channels use different values for the group name, multicast address and multicast port.

To isolate JGroups channels for different services on the same set of AS instances from each other, you MUST change the group name and the multicast port. In other words, each channel must have its own set of values.

For example, say we have a production cluster of 3 machines, each of which has an HAPartition deployed along with a JBoss Cache used for web session clustering. The HAPartition channels should not communicate with the JBoss Cache channels. They should use a different group name and multicast port. They can use the same multicast address, although they don't need to.

To isolate JGroups channels for the same service from other instances of the service on the network, you MUST change ALL three values. Each channel must have its own group name, multicast address, and multicast port.

For example, say we have a production cluster of 3 machines, each of which has an HAPartition deployed. On the same network there is also a QA cluster of 3 machines, which also has an HAPartition deployed. The HAPartition group name, multicast address, and multicast port for the production machines must be different from those used on the QA machines.