Using F5 as default gateway in Amazon AWS

Hi,

The security group connected to F5 and Test1 are open for any. The network ACL is open for any in the public and test subnet.

I have a Virtual Server that is configured with SNAT Automap and this works as a charm for incoming traffic to F5 which then sends it to the test network and a reply back to the Internet.

My problem is that network traffic origin from my test network gets the external IP of the NAT instance which is different from my F5 external IP. My customers has only the F5 external IP whitelisted in their firewalls, not the NAT instance external IP.

See below picture for a better understanding of my problem:

The blue arrow shows how the traffic is flowing today when I start a connection from my Test1 server. I want the traffic to flow like the yellow arrow.

To fix this I thought I could create a NAT rule stating that all traffic origin from 10.0.16.0/24 towards 0.0.0.0/0 should NAT to the external IP of F5. This rule is enabled on the Test network VLAN. The strange thing is that I don't see any hits on the statistics for this NAT rule and I cant access Internet. Test1 server has the default gateway of F5 interface on the Test network. So what am I doing wrong?

Thank you for your time.