Technical Tip: Configure jumbo frame support

[mp2]

Description
This article describes how to configure jumbo frame support for standalone FortiSwitch.

Related links:
https://docs.fortinet.com/product/fortiswitch/6.2

FSW CLI guide (system interface configuration): page 136.
https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/0e7e2291-c2e2-11e9-8977-005056...

Solution
By default, FortiSwitch internal interface is configured with MTU size 1500.
Configure MTU-override on the system internal interface to support jumbo frames is possible.
This particular system interface needs to configured with static mode of IP address.
DHCP mode of IP addressing is not supported for configuring jumbo frames.

# config system interface
    edit internal
        set mode static
        set ip xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy     <----- 'x' is the IP address and 'y' is the subnet mask.
        set mtu-override enable
        set mtu <MTU-value> ===default 1500
    end

Note.
Set MTU ranges from 68- 10000.(interface has static mode of IP).
Once MTU size is changed, reboot the FortiSwitch to update the MTU values of the VLANs on this interface.

Verify the configuration:

FSW# show full system interface <internal>

Similar configuration can be done for managed FortiSwitch as well to support jumbo frames.