problem when using JCS with load balancer

I have two servers and i want to replicate cache between them. If i use stub and send one request to one server and other request to second server , cache data seem to get replicated in both server and my requests are processed as excpected.
When i use load balancer to redirect my request to both server using round robin then cache data in both server doesnt get replicated or shared.
Can u please tell me what goes wrong when i m using load balancer