FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 269894
Description This article describes how to tune TCP maximum segment size in explicit proxy FortiGate.
Scope FortiGate.

In the FortiGate common firewall policy, it is possible to tune the TCP maximum segment size as commands below:


config firewall policy 

    edit 1

        set tcp-mss-sender <value>

        set tcp-mss-receiver <value>



But there is no such option or command in explicit proxy policy when TCP maximum segment size issue is encountered,

so it is possible to tune TCP maximum size on the interface as commands below:


config system interface

    edit <interface name>

        set tcp-mss <value>