snat routing issue - need clarification

If you set up your servers to use the BIG-IP as their default gateway, traffic incoming to the servers will (if enabled) follow the auto lasthop path to return to sender. This is a layer 2 mechanism that records the last "hop" or router and returns to it. On the other hand, now that the BIG-IP is the servers' default gateway, any traffic originating from the server to the world (ie. antivirus updates, etc.) will need a forwarding virtual (listening on the internal interface).