Technical Tip: Enabling the JUMBO frames on the FortiSwitches managed via FortiLink

Description

This article describes how to enable Jumbo frames on the FortiSwitches that are managed by the FortiGate (via FortiLink).

Scope

FortiGate v6.4, v7.0, v7.2.8 and v7.4, FortiSwitch: v6.4, v7.0, v7.2.3 and v7.4.

Solution

1. Enable Jumbo frame on the FortiLink interface:

config system interface
    edit "fortilink"
        set mtu-override enable
        set mtu 9000
    next
end

The MTU will be valid for all the VLANs defined within the FortiLink interface.

Note: If the physical member port is not mentioned, the MTU cannot be set higher than 1500.

No physical port is configured on the following example FortiLink interface:

config system interface
    edit "fortilink"
        set vdom "root"
        set fortilink enable
        set ip x.x.x.x
        set allowaccess ping fabric
        set type aggregate
        set lldp-reception enable
        set lldp-transmission enable
        set snmp-index 42
        set mtu-override enable
    next
end

MTU is capped at 1500:

FGT(fortilink) # set mtu
<integer> Maximum transmission unit (68-1500). Default 1500.

When the port is mentioned, the MTU can be set higher than 1500. In the following:

• Port8, the physical port, is mapped.
  
  

FGT(fortilink) # show
    config system interface
        edit "fortilink"
            set vdom "root"
            set fortilink enable
            set ip x.x.x.x
            set allowaccess ping fabric
            set type aggregate
            set member "port8"
            set lldp-reception enable
            set lldp-transmission enable
            set snmp-index 42
            set mtu-override enable
        next
    end

The MTU can be set above 1500 here:

FGT(fortilink) # set mtu
<integer> Maximum transmission unit (256-9216). Default 1500. 

2. Make sure that all the physical ports are configured with max frame size where JUMBO frames are required. This needs to be enabled on the ports that are part of the FortiLink trunk and the ports where the server or SAN devices are connected.

The following setting needs to be configured on the switch side, because the switch side calls the FortiLink trunk, and the FortiGate calls the FortiLink interface.

config switch physical-port
    edit "port1"
        set max-frame-size 9216
        set speed auto
        set status up
        set storm-control-mode disabled
    next
end        

3. Configure the internal interface with a static IP address to enable the MTU override option. Then set the MTU to 9000.

config system interface
    edit "internal"
        set ip 10.255.1.3 255.255.255.0
        set allowaccess ping https ssh
        set type physical
        set snmp-index 58
        set mtu-override enable
        set mtu 9000
    next
end

After completing step 3, reboot the FortiSwitch for the changes to take effect on all the configured VLANs (this is mandatory).

Verification for jumbo frames:

Create a VLAN called JUMBO: 192.168.15.1/24 under the FortiLink interface. Make sure to enable the Ping under the VLAN settings:

config system interface
    edit "JUMBO"
        set vdom "root"
        set ip 192.168.15.1 255.255.255.0
        set allowaccess ping
        set device-identification enable
        set role lan
        set snmp-index 49
        set ip-managed-by-fortiipam disable
        set interface "fortilink"
        set vlanid 301
    next
end

Next, a virtual interface was created on the FortiSwitch with the same name as shown below:

config system interface
    edit "JUMBO"
        set ip 192.168.15.10 255.255.255.0
        set snmp-index 65
        set vlanid 301
        set interface "internal"
    next
end

Setting up the ping options with data size 8960 and the df bit set to yes:

With these settings:

S648FFTV23-----5 # execute ping-options data-size 8900
S648FFTV23-----5 # execute ping-options df-bit yes
 
S648FFTV23-----5 # execute ping-options view-settings
Ping Options:
        Repeat Count: 5
        Data Size: 8960
        Timeout: 2
        Interface: auto
        Interval: 1
        TTL: 64
        TOS: 0
        DF bit: set
        Source Address: auto
        Pattern:
        Pattern Size in Bytes: 0
        Validate Reply: no
        Adaptive Ping: disable
 
S648FFTV23-----5 # execute ping 192.168.15.1
PING 192.168.15.1 (192.168.15.1): 8960 data bytes
8968 bytes from 192.168.15.1: icmp_seq=0 ttl=255 time=0.5 ms
8968 bytes from 192.168.15.1: icmp_seq=1 ttl=255 time=0.4 ms
8968 bytes from 192.168.15.1: icmp_seq=2 ttl=255 time=0.4 ms
8968 bytes from 192.168.15.1: icmp_seq=3 ttl=255 time=0.4 ms
8968 bytes from 192.168.15.1: icmp_seq=4 ttl=255 time=0.3 ms
 
--- 192.168.15.1 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 0.3/0.4/0.5 ms

For entry-level FortiSwitch (E and F), use the commands below:

config switch global
    set max-frame-size 1500
end

Reference articles:

• Technical Tip: Configure jumbo frame support

• Technical Tip: Configure Jumbo Frame in FortiSwitch