Routing of the Virtual IP

You need to make sure that the response of the selected pool member will be routed to the BigIP. If the pool members do not have a (preferrably floating) self IP of the BigIP configured as default gateway, you could for example use SNAT to make the BigIP appear as the client (source IP) to the selected pool member. When the response arrived at the BigIP, it will then route the response back to the last L2 hop it has seen when the request arrived using a feature called auto lasthop (by default). See K13876 for a description of this feature.

HTH

Martin