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

[gvenkatesan]

Description	This article explains the recommended configuration and the firmware that needs to be present on the FortiExtender-511F to let it forward the DHCP packets as expected via the LTE interface connecting to a private 5G VPN network.
Scope	FortiExtender-511F (managed, standalone) v 7.6.1(Build 0411) GA and above, Modem Firmware: FEM_RM502Q-23.1.1-build0006-R13_ptcrb.out.
Solution	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