Technical Tip: How to configure PPPoE connection with VLAN tag

[vrajendran]

Description
This article describes how to identify if a PPPoE connections is using a VLAN and how to configure it in the FortiGate.
Solution
1) Identify if the modem is using a VLAN:

To confirm if there is VLAN configured in the modem run the following sniffer in the FortiGate:

#diagnose sniffer packet wan1 'none' 4 0 l

'WAN1' is the name of the interface connected to the modem.
 There is a VLAN configured in the modem visible using the following command:

# dia sniffer packet wan1 'none' 4 0 l
interfaces=[wan1]
filters=[none]
pcap_lookupnet: wan1: no IPv4 address assigned
2017-02-21 14:10:29.694913 wan1 -- pppoe printer hasn't been added to sniffer
2017-02-21 14:10:29.702087 wan1 -- 802.1Q vlan#1780 P6 
2017-02-21 14:10:30.690632 wan1 -- pppoe printer hasn't been added to sniffer
2017-02-21 14:10:30.696940 wan1 -- 802.1Q vlan#1780 P6
2017-02-21 14:10:32.690714 wan1 -- pppoe printer hasn't been added to sniffer
2017-02-21 14:10:32.698379 wan1 -- 802.1Q vlan#1780 P6

This output also displays how the unit is receiving packets with VLAN tag 1780.

There is also the possibility to do a sniffer with verbose 6 to convert in pcap file.

2) confirm the modem is using a VLAN and also the VLAN ID, in this example the VLAN ID is:1780.

3) Configure the VLAN in the unit and associate it to the physical interface connected to the modem.

In this case the VLAN ID is: 1780 and the physical interface is: 'WAN1'.

Here a CLI example, also can be done through the GUI:

# config system interface
    edit "1780"
        set vdom "root"
        set mode pppoe
set username "username@example.com"
        set password "password"
        set interface "wan1"
        set vlanid 1780
    next
end

After this configuration the PPPoE connection is established.