HTTP full transparent proxy balancing

thanks for the clue, but it seems the persistent profiles are only applicable on the client side. I try to describe the essence of the problem.

C - client's IP address

S - webserver's IP address

I have couple of full transparent proxy servers. To balance incoming request from the client is no problem - I have created wildcard virtual server which forwards the packet to one of the proxy servers, without changing the IP header - it is still src_IP=C, dest_IP=S.

The proxy server is (can behave as) full proxy device, so it sends the packet to the internet again without changing the IP header (src=C, dst=S). This packet goes to Internet again through the F5 box, which acts currently only as a router (IP forwarding virtual server).

And now we get to the core of the problem. The webserver sends the response (src_IP=S,dest_IP=C). Routing make sure the packet arrives on the F5 box. And right now I need F5 box to forward this packet to the relevant proxy server, but the IP header doesn't contain such information (it is src_IP=S,dest_IP=C).

I suppose there must be created some persistence record somewhere. May be when the load-balancing decision is made? We have all information to identify the session - client's IP, server's IP, selected proxy server. And then it should be somehow applied to the incoming packets.

Or

when the packet leaves the proxy server and is forwarded by F5 box to Internet? For example based on the client's IP, webserver's IP and the proxy' server's MAC address?

May be this approach is completely wrong. I don't now how the F5 handle the flows. Of course I can always use the trick with X-forwarded-for line in HTTP header, but I believe the F5 can handle it more elegant way :-).

Please help.

Vilem