This article describes a known issue with FortiGate 60xF models, where users are reporting direct attached copper cable not functioning on the ultra-low latency ports with 25G speed.
Scope
FortiGate 60xF and FortiOS v7.2 or later.
Solution
FortiGate 60xF(600F and 601F) models have 4 ultra-low latency ports X5 to X8 which supports both 10G and 25G speeds. By default, these ports work as 10G SFP+. To change the mode to 25G follow the below guide:
FortiGate 600F and 601F fast path architecture
Direct attached copper (DAC) cable or breakout DAC cable can be used with these ultra-low latency ports at 25G speed. However, DAC cable requires CR mediatype on these ports to function that is not yet supported on these models.
In some instances on FortiGate 60xF models, DAC cable or breakout DAC cable can function with SR media type on 25G in FortiOS v7.0.x.
However, upon upgrading to FortiOS v7.2.x or v7.4.x, compatibility issues arise which causes the DAC cable to not function as expected. The recommendation is not to use SR/LR media types with a directly attached copper cable as it may cause stability issues.
The CR media type feature for 25G speed is scheduled to be added in upcoming FortiOS v7.2.9 and v7.4.5 for FortiGate 60xF models.
Note: SR and LR media types should be used with fiber connections and direct-attached copper (DAC) cable should be used with CR media type.