load balancer in same VLAN

Main idea is to have the BIG-IP in the traffic path between the client and the server for both requests and their responses. If the BIG-IP, clients and servers are sitting in same network, you need to do NATting to force the return packets back via the BIG-IP instead of going directly. This is normally done with SNAT Automap in the virtual server configuration. You may need to add information of the client IP if the server needs it as using SNAT will lose it. This can be done by adding an X-FORWARDED-FOR header into the request (in HTTP profile). You may need to add routes, too, depending on your actual topology.

More information how to configure is here: Configuring a One-IP Network Topology