In this post, I will show you guys how to setup a Cisco ASA firewall serves as a layer 3 packet transfer device. The example will be demonstrate with 192.168.3.10/32 machine accessing to 18.104.22.168/32 via IPerf. There is only simple routing and has no NAT involve.
In this setup, the ASA is acting as the gateway between office network and the internet. The 192.168.3.0/24 is the internal subnet and 10.0.0.20/30 is the internet. There are couple areas we have to handle, and they are routing, and policy. Since ASA is a stateful device, we have to apply policy to allow internal network to access external network, but not vise versa.