Hey Soumen
Can you please explain a bit further regarding the different traffic flows? When is the client's seeing the SNAT address?
Since the BIG-IP is a Full Proxy, there will be one TCP connection between the Client and the BIG-IP and one TCP connection between the BIG-IP and the Server.
You are correct that when a client communicates with the VIP, it will only see traffic between itself and the VIP. And on the server side, if you have SNAT enabled on your virtual server, the server side connection will see the SNAT IP address.
To give you an example, here is the traffic flows of my client, communicating with the BIG-IP and the BIG-IP with the server. The .33 addresss is my floating self-IP address on that VLAN:
[root@bigipcore02:Active:Changes Pending] config tmsh show sys connection cs-server-addr 10.10.15.245
Sys::Connections
10.10.10.111:42012 10.10.15.245:80 10.10.15.33:42012 10.10.15.10:80 tcp 25 (tmm: 0) none
Is it possible for you to share the printscreen of the traffic?