FortiGate devices with NP6 (Network Processor 6) acceleration offload traffic directly to hardware, bypassing the CPU for improved performance. When auto-asic-offload is enabled in a firewall policy, most of the traffic does not reach the CPU, which means it won't be captured by the standard sniffer trace command.
Since NP6-accelerated traffic is handled entirely in hardware, only a small portion of initial packets (such as session setup packets or exceptions) might be seen in the sniffer output. To capture all packets, the administrator must disable hardware offloading using:
config firewall policy
edit <policy_ID>
set auto-asic-offload disable
end
Disabling ASIC offload forces traffic to be processed by the CPU, allowing the sniffer tool to capture all packets.

The set tcp-mss-sender and set tcp-mss-receiver commands in a firewall policy allow an administrator to adjust the Maximum Segment Size (MSS) of TCP packets.
This setting controls the largest payload size that a device can handle in a single TCP segment, ensuring that packets do not exceed the allowed MTU (Maximum Transmission Unit) along the network path.
set tcp-mss-sender adjusts the MSS value for outgoing TCP traffic. set tcp-mss-receiver adjusts the MSS value for incoming TCP traffic.
This helps prevent issues with fragmentation and MTU mismatches, improving network performance and avoiding retransmissions.

FortiGate, like other security appliances, cannot analyze encrypted HTTPS traffic unless itdecryptsit first. If only certificate inspectionis enabled, FortiGate can see the certificate details (such as the domain and issuer) butcannot inspect the actual web content.
To fully analyze the traffic and detect potential malware threats:
#Full SSL inspection (Deep Packet Inspection)must be enabled in theSSL/SSH Inspection Profile.
# This allows FortiGate todecrypt the HTTPS traffic, inspect the content, and then re-encrypt it before forwarding it to the user.
# Without full SSL inspection, threats embedded in encrypted traffic may go undetected.

When FortiGate is operating inproxy modewithfull SSL inspection enabled, it inspects encrypted HTTPS traffic by default onport 443. However, some websites may usenon-standard HTTPS ports(such as 8443), which FortiGate does not inspect unless explicitly configured.
To ensure that FortiGate inspects HTTPS traffic onport 8443, administrators mustmanually add port 8443in theProtocol Port Mappingsection of theSSL/SSH Inspection Profile. This allows FortiGate to treat HTTPS traffic on port 8443 the same as traffic on port 443, enabling proper inspection and enforcement of FortiGuard category-based web filtering.

FortiGate's IPS protocol decoders analyze network transmission patterns and application signatures to identify and block malicious traffic. Application Control is the feature that allows FortiGate to detect, classify, and block applications based on their behavior and signatures, even when they do not rely on traditional URLs.
Application Control works alongside IPS protocol decoders to inspect packet payloads and enforce security policies based on recognized application behaviors. It enables granular control over non-URL-based applications such as P2P traffic, VoIP, messaging apps, and other non- web-based protocols that IPS can identify through protocol decoders. IPS and Application Control together can detect evasive or encrypted applications that might bypass traditional firewall rules.