insert_xforwarded verification

The easiest is to tcpdump the traffic (Or ssldump if it's encrypted).

On the bigip it'd be something like

tcpdump -i 0.0 -nn  -e -s0 -X host BACKEND_IP_ADDR and port BACKEND_PORT

-i == specie the interface. 0.0 will snoop all interfaces

-nn == don't translate ip's or ports to names

-e == print the link level header when dumping the traffic

-s0 == capture all packets. Default is just the first 64

-X == dump the packet as ASCII not just numbers

The rest is the filter. We want packets that are to/from the backend host and on the port you're talking to.