If a FortiGate or VDOM is configured for proxy-based inspection then a mixture of flow-based and proxy-based inspection occurs. Packets initially encounter the IPS engine, which uses the same steps described in UTM/NGFW packet flow: flow-based inspection to apply single-pass IPS and Application Control if configured in the firewall policy accepting the traffic.
The packets are then sent to the FortiOS UTM/NGFW proxy for proxy-based inspection. The proxy first determines if the traffic is SSL traffic that should be decrypted for SSL inspection. SSL traffic to be inspected is decrypted by the proxy. SSL decryption is offloaded to and accelerated by CP8 or CP9 processors.
Proxy-based inspection extracts and caches content, such as files and web pages, from content sessions and inspects the cached content for threats. Content inspection happens in the following order: VoIP inspection, DLP, Anti-Spam, Web Filtering, AntiVirus, and ICAP.
If no threat is found the proxy relays the content to its destination. If a threat is found the proxy can block the threat and replace it with a replacement message.
Decrypted SSL traffic is sent to the IPS engine (where IPS and Application Control can be applied) before re-entering the proxy where actual proxy-based inspection is applied to the decrypted SSL traffic. Once decrypted SSL traffic has been inspected it is re-encrypted and forwarded to its destination. SSL encryption is offloaded to and accelerated by CP8 or CP9 processors. If a threat is found the proxy can block the threat and replace it with a replacement message.
The proxy can also block VoIP traffic that contains threats. VoIP inspection can also look inside VoIP packets and extract port and address information and open pinholes in the firewall to allow VoIP traffic through.
ICAP intercepts HTTP and HTTPS traffic and forwards it to an ICAP server. The FortiGate is the surrogate, or “middle-man”, and carries the ICAP responses from the ICAP server to the ICAP client; the ICAP client then responds back, and the FortiGate determines the action that should be taken with these ICAP responses and requests.