Are you trying to ping the node using ICMP or open a TCP connection? If ICMP, you'd need to configure the virtual server for all protocols as opposed to TCP or UDP.
If you're not able to establish a TCP connection through the forwarding virtual server, you could try running a tcpdump on all interfaces and then initiate a TCP connection. Here's an example that would capture traffic on all interfaces (0.0) to/from any hosts on or from port 22:
tcpdump -n -i 0.0 tcp port 22
If you find that the requests and responses through the BIG-IP aren't symmetrical, you would need to enable loose initiation and loose close on the FastL4 profile to instruct BIG-IP to allow the packets through (
Click here).
Aaron