Using F5 as a Proxy

Perhaps the documentation falls short here, because whereas the information is present, this seems to be a universal problem with understanding how the product works. The BigIP in version 4 had a checkbox where you could enable ip forwarding globally. In version 9, the box is essentially default deny, and any forwarding needs to be configured via a virtual server. This can be done specifically to meet a need, or you can configure a route-all virtual server:

virtual forward-all {
   ip forward
   destination any:any
   mask none
}

This will forward all traffic as long as there is a matching route in the routing table.