Technical Tip: Changing the speed of a FortiGate interface
Description
This article describes how to change the port speed of a FortiGate interface via CLI. There is no option to change the interface speed via GUI, this change can only be performed via CLI
Scope
FortiGate.
Solution.
Configuration:
- The default value for all interfaces is auto-negotiate. This should automatically set the speed for that port appropriate to the speed set on the other network hardware. If this does not happen, edit the configuration using the following CLI commands:

- The interface speed.
- Auto is the default speed. The interface uses auto-negotiation to determine the connection speed. Change the speed only if the interface is connected to a unit that does not support auto-negotiation. If the speed is mismatched on both ends, then the interface status on FortiGate will show as DOWN. Therefore, it is important to know the speed of the other end, and according to that, changes can be made on the FortiGate.
- 10full, 10 Mbps, full duplex.
- 10half, 10 Mbps, half duplex.
- 100full, 100 Mbps, full duplex.
- 100half, 100 Mbps, half duplex.
- 1000full, 1000 Mbps, full duplex.
- 1000half, 1000 Mbps, half duplex.
- However, a command in the config system globally allows the internal switch speed to be set.
- If the ports are part of the internal hardware switch, then it is possible to change it using 'config system virtual-switch'.
Troubleshooting.
For interface diagnostics:
diagnose hardware deviceinfo nic <interface-name>
Changing the port speed on an already aggregated interface is not possible.
Refer to the related article Troubleshooting Tip: FortiGate interface error counters for more information on understanding the output of this diagnostic command.
The following error may appear: 'Interface speed cannot be set for aggregated interfaces. Command fail. Return code -218'. Therefore, it is necessary to remove the interfaces from the aggregation, change the speed, and then add them again to the aggregation.
Note:
If the port is down once enabled, it comes on half-duplex. Connect a PC or Layer 2 switch (whatever device that does not generate DHCP) and apply the commands below, then the interface will come back on in 1 gigabit (or any desired speed) with full duplex:
config system interface
edit <port name>
set speed 1000full
set status up
end
Related documents:
Config system virtual switch - FortiGate CLI reference.
Configuring port speeds - moved from Public to INTERNAL.
Technical Tip: Configure Ethernet speed, duplex and negotiation settings.
Troubleshooting Tip: FortiGate interface error counters.
