Technical Tip: How to configure PPPoE interface when ISP provides only VLAN ID

Step 1: Create a VLAN interface/sub-interface under the required physical interface.

Follow the following KB article for creating VLAN-tagged sub-interface:

Technical Tip: How to create a VLAN tagged interface (802.1q) on a FortiGate - tagged/untagged traffic

Make sure to select the role of the interface as WAN.

Example of configuration command in CLI:

config system interface
    edit "pppoe"                                               <-- Name of sub-interface.

        set role wan                                       <-- Always select role WAN.
        set interface "port3"                         <-- Bind it to the required physical interface, port 3 is used as an example.
        set vlanid 20                                     <-- Mention the VLAN ID that the ISP has been given. 'vlanid 20' is used as an example.
       next
end

Step 2: Configure PPPoE configuration commands as shown below:

config system interface
    edit "pppoe"
        set vdom "root"
        set mode pppoe
        set username "<xxxxxx>"           <-- Provide the username.
        set password "<yyyyyy">           <-- Provide the required password.
    next
end

Starting FortiOS v7.4.7 and above, the PPPoE option is available on GUI by default. Also, configuration will be retained in case the addressing mode is set to other modes then back to PPPoE.

To configure, go to Network -> Interface -> Create New -> Interface.

By default, the 'Retrieve default gateway from server' is enabled. This will automatically populate the default route for the PPPoE interface.

To modify the distance and priority, refer to the article: Technical Tip: Changing Distance and Priority of Default Gateway Learned from PPPoE

To troubleshoot issues regarding PPPoE, follow this article: Technical Tip: Troubleshooting PPPoE connection failed.

Related articles:

Technical Tip: How to create a VLAN tagged interface (802.1q) on a FortiGate - tagged/untagged traffic

Technical Tip: PPPoE-interface configuration

Technical Tip: Troubleshooting PPPoE connection failed