I have tried Vertical Clustering Successfully with 4 tomcat instances & 1 apache server for load balancing. But when tried Horizontal Clustering, I am getting these issues:

Setup : 2 Instances each on 2 servers. 1 Apache webserver for load balancing.

Issue : Session replication & Multicast communication using Apache Tribes doesnt work but fail-over happens quite normally when I shutdown one instance.

Does session replication & cluster commnucation using Apache Tribes requires Multicast Mode enabled in Windows 2003 server NLB properties setup?

Thanks,
Prashant Malshette