Persistence through a firewall

Hi guys,

I have a serious problem with my LVS...

here is my configuration:

1  firewall with ip:192.168.4.1

1  loadbalancer with RIP: 192.168.4.20 and VIP:192.168.4.21

3 real servesr with address 192.168.5.1    192.168.5.2    192.168.5.3
   (the three real server support PERSISTENCE for the http request)

my problem is that I want to do persistence, but after the client connect 
through the firewall, the load balancer sees always the same source IP 
address : 192.168.4.1 (IP from the firewall)
so teh load balancer send all of the connections the same real server

>ipvsadm -l -c
pro expire state       source             virtual            destination
TCP 14:54  ESTABLISHED 192.168.4.1:1847   192.168.4.21:http  
192.168.5.59:http
TCP 14:54  ESTABLISHED 192.168.4.1:2203   192.168.4.21:http  
192.168.5.59:http
TCP 14:54  ESTABLISHED 192.168.4.1:1890   192.168.4.21:http  
192.168.5.59:http
TCP 14:54  ESTABLISHED 192.168.4.1:3302   192.168.4.21:http  
192.168.5.59:http


is there something in the ipvs that i need to change?

p.s. the problem is not the firewall because another computer behind the 
firewall is able to see the real IP from the client. the iptables on the 
loadbalancer is desactivated.


thanks in advance for  your help and time.