Technical Tip: How to configure the FortiExtender-511F to forward the DHCP packets via the LTE interface

Scenario:

Client device on VLAN 1 (192168.1.1/24 which relays DHCP packets to 10.10.10.101)---> FortiGate --> FortiExtender-511F--------> LTE 5G VPN network ------> Private DHCP server located in the data center(10.10.10.101)

• The end client device connecting via VLAN 1 will request the IP via the DHCP process.
• The FortiGate will relay this DHCP Discover packet as a unicast since the VLAN 1 is configured to relay the DHCP requests to the private DHCP server.
• The relayed DHCP packet will be a layer-3 unicast, which will be sent to the private VPN network via the LTE interface on the FortiExtender-511F device.

By default, the FortiExtender-511F, will not forward any of the DHCP packets via the LTE interface until the following conditions are met:

• FortiExtender-511F must be operating on v7.6.1 GA.
• The modem firmware must be FEM_RM502Q-23.1.1-build0006-R13_ptcrb.out.
• 'private network' mode must be enabled under the LTE plan.

FortiExtender-511F standalone config:

config lte plan
  edit "Telstra" <----- As a best practice, the LTE plan name should match the carrier network provider's name.
    set private-network enable
  next
end

FortiExtender-511F managed config:

• If SIM slot 1 is in use, configure the plan according to the LTE/5G network carrier's recommendations. To forward DHCP packets, enable 'Private Network' mode as shown in the screenshot below:

• Assign this plan to the FortiExtender profile that is currently assigned to the FortiExtender-511F