VLAN

Virtual local area networks (VLANs) multiply the capabilities of your FortiGate and can also provide added network security. VLANs use ID tags to logically separate devices on a network into smaller broadcast domains. These smaller domains forward packets only to devices that are part of that VLAN domain. This reduces traffic and increases network security.

VLANs in NAT mode

In NAT mode, the FortiGate unit functions as a layer-3 device. In this mode, the FortiGate unit controls the flow of packets between VLANs and can also remove VLAN tags from incoming VLAN packets. The FortiGate unit can also forward untagged packets to other networks such as the Internet.

In NAT mode, the FortiGate unit supports VLAN trunk links with IEEE 802.1Q‑compliant switches or routers. The trunk link transports VLAN-tagged packets between physical subnets or networks. When you add VLAN subinterfaces to the FortiGate's physical interfaces, the VLANs have IDs that match the VLAN IDs of packets on the trunk link. The FortiGate unit directs packets with VLAN IDs to subinterfaces with matching IDs.

You can define VLAN subinterfaces on all FortiGate physical interfaces. However, if multiple virtual domains are configured on the FortiGate unit, you only have access to the physical interfaces on your virtual domain. The FortiGate unit can tag packets leaving on a VLAN subinterface. It can also remove VLAN tags from incoming packets and add a different VLAN tag to outgoing packets.

Normally in VLAN configurations, the FortiGate unit's internal interface is connected to a VLAN trunk, and the external interface connects to an Internet router that is not configured for VLANs. In this configuration, the FortiGate unit can apply different policies for traffic on each VLAN interface connected to the internal interface, which results in less network traffic and better security.

Sample topology

In this example, two different internal VLAN networks share one interface on the FortiGate unit and share the connection to the Internet. This example shows that two networks can have separate traffic streams while sharing a single interface. This configuration can apply to two departments in a single company or to different companies.

There are two different internal network VLANs in this example. VLAN_100 is on the 10.1.1.0/255.255.255.0 subnet, and VLAN_200 is on the 10.1.2.0/255.255.255.0 subnet. These VLANs are connected to the VLAN switch.

The FortiGate internal interface connects to the VLAN switch through an 802.1Q trunk. The internal interface has an IP address of 192.168.110.126 and is configured with two VLAN subinterfaces (VLAN_100 and VLAN_200). The external interface has an IP address of 172.16.21.2 and connects to the Internet. The external interface has no VLAN subinterfaces.

When the VLAN switch receives packets from VLAN_100 and VLAN_200, it applies VLAN ID tags and forwards the packets of each VLAN both to local ports and to the FortiGate unit across the trunk link. The FortiGate unit has policies that allow traffic to flow between the VLANs, and from the VLANs to the external network.

Sample configuration

In this example, both the FortiGate unit and the Cisco 2950 switch are installed and connected and basic configuration has been completed. On the switch, you need access to the CLI to enter commands. No VDOMs are enabled in this example.

General configuration steps include:

1. Configure the external interface.

2. Add two VLAN subinterfaces to the internal network interface.

3. Add firewall addresses and address ranges for the internal and external networks.

4. Add security policies to allow:

   • the VLAN networks to access each other.

   • the VLAN networks to access the external network.

To configure the external interface:

config system interface
    edit external
        set mode static
        set ip 172.16.21.2 255.255.255.0
    next
end

To add VLAN subinterfaces:

config system interface
    edit VLAN_100
        set vdom root
        set interface internal
        set type vlan
        set vlanid 100
        set mode static
        set ip 10.1.1.1 255.255.255.0
        set allowaccess https ping
    next
    edit VLAN_200
        set vdom root
        set interface internal
        set type vlan
        set vlanid 200
        set mode static
        set ip 10.1.2.1 255.255.255.0
        set allowaccess https ping
    next
end

To add the firewall addresses:

config firewall address
    edit VLAN_100_Net
        set type ipmask
        set subnet 10.1.1.0 255.255.255.0
    next
    edit VLAN_200_Net
        set type ipmask
        set subnet 10.1.2.0 255.255.255.0
    next
end

To add security policies:

Policies 1 and 2 do not need NAT enabled, but policies 3 and 4 do need NAT enabled.

config firewall policy
    edit 1
        set srcintf VLAN_100
        set srcaddr VLAN_100_Net
        set dstintf VLAN_200
        set dstaddr VLAN_200_Net
        set schedule always
        set service ALL
        set action accept
        set nat disable
        set status enable
    next
    edit 2
        set srcintf VLAN_200
        set srcaddr VLAN_200_Net
        set dstintf VLAN_100
        set dstaddr VLAN_100_Net
        set schedule always
        set service ALL
        set action accept
        set nat disable
        set status enable
    next
    edit 3
        set srcintf VLAN_100
        set srcaddr VLAN_100_Net
        set dstintf external
        set dstaddr all
        set schedule always
        set service ALL
        set action accept
        set nat enable
        set status enable
    next
    edit 4
        set srcintf VLAN_200
        set srcaddr VLAN_200_Net
        set dstintf external
        set dstaddr all
        set schedule always
        set service ALL
        set action accept
        set nat enable
        set status enable
    next
end

VLANs in transparent mode

In transparent mode, the FortiGate unit behaves like a layer-2 bridge but can still provide services such as antivirus scanning, web filtering, spam filtering, and intrusion protection to traffic. Some limitations of transparent mode is that you cannot use SSL VPN, PPTP/L2TP VPN, DHCP server, or easily perform NAT on traffic. The limits in transparent mode apply to IEEE 802.1Q VLAN trunks passing through the unit.

You can insert the FortiGate unit operating in transparent mode into the VLAN trunk without making changes to your network. In a typical configuration, the FortiGate unit internal interface accepts VLAN packets on a VLAN trunk from a VLAN switch or router connected to internal network VLANs. The FortiGate external interface forwards VLAN‑tagged packets through another VLAN trunk to an external VLAN switch or router and on to external networks such as the Internet. You can configure the unit to apply different policies for traffic on each VLAN in the trunk.

To pass VLAN traffic through the FortiGate unit, you add two VLAN subinterfaces with the same VLAN ID, one to the internal interface and the other to the external interface. You then create a security policy to permit packets to flow from the internal VLAN interface to the external VLAN interface. If required, create another security policy to permit packets to flow from the external VLAN interface to the internal VLAN interface. Typically in transparent mode, you do not permit packets to move between different VLANs. Network protection features such as spam filtering, web filtering, and anti-virus scanning, are applied through the UTM profiles specified in each security policy, enabling very detailed control over traffic.

When the FortiGate unit receives a VLAN-tagged packet on a physical interface, it directs the packet to the VLAN subinterface with the matching VLAN ID. The VLAN tag is removed from the packet and the FortiGate unit then applies security policies using the same method it uses for non-VLAN packets. If the packet exits the FortiGate unit through a VLAN subinterface, the VLAN ID for that subinterface is added to the packet and the packet is sent to the corresponding physical interface.

Sample topology

In this example, the FortiGate unit is operating in transparent mode and is configured with two VLANs: one with an ID of 100 and the other with ID 200. The internal and external physical interfaces each have two VLAN subinterfaces, one for VLAN_100 and one for VLAN_200.

The IP range for the internal VLAN_100 network is 10.100.0.0/255.255.0.0, and for the internal VLAN_200 network is 10.200.0.0/255.255.0.0.

The internal networks are connected to a Cisco 2950 VLAN switch which combines traffic from the two VLANs onto one in the FortiGate unit's internal interface. The VLAN traffic leaves the FortiGate unit on the external network interface, goes on to the VLAN switch, and on to the Internet. When the FortiGate units receives a tagged packet, it directs it from the incoming VLAN subinterface to the outgoing VLAN subinterface for that VLAN.

In this example, we create a VLAN subinterface on the internal interface and another one on the external interface, both with the same VLAN ID. Then we create security policies that allow packets to travel between the VLAN_100_int interface and the VLAN_100_ext interface. Two policies are required: one for each direction of traffic. The same is required between the VLAN_200_int interface and the VLAN_200_ext interface, for a total of four security policies.

Sample configuration

There are two main steps to configure your FortiGate unit to work with VLANs in transparent mode:

1. Add VLAN subinterfaces.
2. Add security policies.

You can also configure the protection profiles that manage antivirus scanning, web filtering, and spam filtering.

To add VLAN subinterfaces:

config system interface
    edit VLAN_100_int
        set type vlan
        set interface internal
        set vlanid 100
    next
    edit VLAN_100_ext
        set type vlan
        set interface external
        set vlanid 100
    next
    edit VLAN_200_int
        set type vlan
        set interface internal
        set vlanid 200
    next
    edit VLAN_200_ext
        set type vlan
        set interface external
        set vlanid 200
    next
end

To add security policies:

config firewall policy
    edit 1
        set srcintf VLAN_100_int
        set srcaddr all
        set dstintf VLAN_100_ext
        set dstaddr all
        set action accept
        set schedule always
        set service ALL
    next
    edit 2
        set srcintf VLAN_100_ext
        set srcaddr all
        set dstintf VLAN_100_int
        set dstaddr all
        set action accept
        set schedule always
        set service ALL
    next
    edit 3
        set srcintf VLAN_200_int
        set srcaddr all
        set dstintf VLAN_200_ext
        set dstaddr all
        set action accept
        set schedule always
        set service ALL
    next
    edit 4
        set srcintf VLAN_200_ext
        set srcaddr all
        set dstintf VLAN_200_int
        set dstaddr all
        set action accept
        set schedule always
        set service ALL
    next
end