VLAN is the acronym for Virtual Local Area Network, it is a virtual partitioning of physical network switches on OSI layer 2.
It is a way to keep network clients separated from each other even if they use the same shared physical network, without setting up a whole subnet and a router. It works by adding a label (VLAN ID) on networking traffic, and using this label to route the traffic to keep isolated clients in different VLANs. To use a VLAN you need at least 2 devices supporting VLAN features (as any route requires at least 2 points), which is usually advanced routers, any OpenWrt device, and any self-respecting PC or single-board computer (Windows, MacOS, Linux and BSDs support VLANs).
Many embedded devices with more than 1 port contain a VLAN-capable switch (all routers with a WAN port have a VLAN-capable switch for example). Single-port devices and devices where there is an ethernet controller for each port (like for example PCEngines boards or most PC hardware in general) will have VLAN managed by OS drivers.
A VLAN-capable switch is an integrated version of an independent device called “managed switch”. It is connected to an internal “ethernet” interface of your device, and it is more or less independent from the main CPU. It can place ports under the same VLAN (and they will communicate with each other) by just setting the right VLAN ID(s) on the ports (with the right configuration, below), and this will work irrespective of the fact that the network communication reaches or not the router CPU itself (do note that to configure the router itself you still need at least one VLAN to reach the CPU).
A device where there is software VLAN support is just a device with many different ethernet controllers, so if you want to place 2 interfaces in the same VLAN, AND you want these two interfaces to also route traffic to-from each other (to act as if they were a VLAN-capable switch as the one I talked about above), you need to bridge them too (i.e. both must be in the same Interface, be it lan, wan or whatever).
If you have any question, feel free to discuss this guide on the OpenWrt forum: https://forum.openwrt.org/t/vlan-assigning
A very common default VLAN configuration on many off-the-shelf routers is the LAN↔WAN separation. OpenWrt default configuration on such devices does usually mirror the stock configuration. Most of such routers only contain a single network interface (eth0), leading to a 5-port VLAN-enabled switch that is virtually partitioned into a LAN and WAN network by using VLANs:
|VLAN ID|| |
|CPU (eth0)||LAN 1||LAN 2||LAN 3||LAN4||WAN|
In this example, VLAN ID of the LAN ports is 1 while the VLAN ID of the WAN port is 2.
Note that the terms “incoming” and “outgoing” and similar refer to network traffic reaching the switch physical ports (or internal CPU port), NOT to traffic that has already entered in the switch.
The router CPU then uses the tag information configured above to know if the data came from VLAN 1 (LAN) or VLAN 2 (WAN) and will then act accordingly. In the default configuration, the CPU will only receive and generate “Tagged” data (as there is no other way for it to tell what is what). The CPU uses driver level VLAN-management for this, as it acts as a single-port device.
Note how the WAN and LAN VLAN IDs in this example do not share any external ports. For any data to cross the WAN and LAN border, it has to pass the CPU on eth0 (where the router and firewall will be filtering the data). As said above, nothing prevents to make VLANs that bypass the CPU entirely.
To find out if the ports of an OpenWrt device consist of several distinct network interfaces, or if it is a single network interface leading to a switch
ls -l /sys/class/net.
Newer devices with embedded switches (like Netgear R7800) use the DSA switch driver, that creates a distinct network interface for each switch port as if they didn't have a switch at all.
Most OpenWrt-supported devices can use the DSA driver, but they aren't ported over yet because the switch configuration would change significantly and likely break any custom setup in devices in the field.
Example: The following ALIX.2D13 has 3 real network interfaces: eth0, eth1 and eth2. Each leads to a single non-switched physical network jack. If needed, you have to use OS-software based VLAN configuration:
# ls -l /sys/class/net ... lrwxrwxrwx 1 root root 0 Jul 25 14:10 eth0 -> ../../devices/pci0000:00/0000:00:09.0/net/eth0 lrwxrwxrwx 1 root root 0 Jul 25 14:10 eth1 -> ../../devices/pci0000:00/0000:00:0a.0/net/eth1 lrwxrwxrwx 1 root root 0 Jul 25 14:10 eth2 -> ../../devices/pci0000:00/0000:00:0b.0/net/eth2
Example: The following TP-Link TL-WDR3600 has only 1 real network interface: eth0. Its 5 physical network jacks belong to a single VLAN-capable switch, that in this example is segmented into 2 VLANs, managed by the switch-hardware : eth0.1 and eth0.2:
# ls -l /sys/class/net ... lrwxrwxrwx 1 root root 0 Jan 1 1970 eth0 -> ../../devices/platform/ag71xx.0/net/eth0 lrwxrwxrwx 1 root root 0 Jul 21 22:13 eth0.1 -> ../../devices/virtual/net/eth0.1 lrwxrwxrwx 1 root root 0 Jul 21 22:13 eth0.2 -> ../../devices/virtual/net/eth0.2
switch section of
/etc/config/network is responsible for partitioning the embedded switch into several VLANs which appear as independent interfaces in the system although they share the same hardware.
This section might not be present on some platforms (depends on specific hardware support). Also, some switches only support 4-bit VLANs.
The example below shows a typical configuration:
config 'switch' 'eth0' option 'reset' '1' option 'enable_vlan' '1' config 'switch_vlan' 'eth0_1' option 'device' 'eth0' option 'vlan' '1' option 'ports' '0 1 3t 5t' config 'switch_vlan' 'eth0_2' option 'device' 'eth0' option 'vlan' '2' option 'ports' '2 4t 5t' config 'switch_vlan' 'eth0_3' option 'device' 'eth0' option 'vlan' '3' option 'ports' '3t 4t' config 'switch_port' option 'device' 'eth0' option 'port' '3' option 'pvid' '3'
Common properties are defined within the
switch section; vlan specific properties are located in additional
switch_vlan sections linked to the
switch section through the
device option; pvid specific properties are found in
switch_port sections linked to the
switch section through the
Ports can be tagged or untagged:
tis appended to the port number) is the one that forces usage of VLAN tags, i.e. when the packet is outgoing, the VLAN ID tag with
vlanvalue is added to the packet, and when the packet is incoming, the VLAN ID tag has to be present and match the configured
pvid) is assigned to the packet automatically. The
pvidvalue can be selected by the
The CPU port (number
5 in our example) may be configured as tagged or untagged, it may even be omitted in the port configuration. The CPU port works like any other ordinary port and can be configured to be tagged or untagged – when the switch routes packet to the CPU port, it appears on the corresponding switch interface (with VLAN ID tag number appended to the interface name in case of a tagged port) as incoming packet to allow software routing (to WiFi for example).
In our example, untagged packet coming to port 0 would be marked as VLAN ID 1 first, then sent to port 1 (untagged, VLAN ID tag removed), port 3 (tagged) and the CPU port (tagged), so the packet appears on
eth0.1 interface. Another packet arriving to port 2 tagged with VLAN ID 2 would be sent to port 4 (tagged) and the CPU port (tagged), the packet appears on
eth0.2 interface. Each tagged switch CPU port has a corresponding interface, in our example you see
eth0.2 in the system (as well as
eth0). When the packet is sent by the software to the tagged CPU port, it has the corresponding VLAN ID assigned automatically. So when the software sends packet to
eth0.2, is is marked with VLAN ID 2 tag automatically first, and then sent to port 2 (untagged, VLAN ID tag removed) and port 4 (tagged).
An untagged port can have only 1 VLAN ID
A driver-level VLAN could be created in the
interface section by adding a dot (
.) and the respective VLAN ID after the interface name (in the
ifname option), like
eth1.2 for VLAN ID 2 on
When any internal software routing decision sends the packet to the software VLAN, it leaves the respective interface (
eth1 in our example) with the VLAN tag present and VLAN ID set to the number corresponding to the interface name (
2 in our example on
If the incoming packet arrives to the interface with software VLANs (incoming packet to
eth1) and has a VLAN ID tag set, it appears on the respective software-VLAN-interface instead (VLAN ID 2 tag arrives on
eth1.2) – if it exists in the configuration! Otherwise the packet is dropped. Non-tagged packets are deliveded to non-VLAN interface (
eth1) as usual.
When you bridge non-VLAN and VLAN interfaces together, the system takes care about adding VLAN ID when sending packet from non-VLAN to VLAN interface, and it automatically removes the VLAN ID when sending packet from VLAN interface to non-VLAN one.
Driver-level VLAN Interfaces may be configured manually. If not, they are created on the fly by netifd. Defining VLANs manually gives more options. The following options are supported:
| ||VLAN Type||no||802.1q||VLAN type, possible values: 8021q or 8021ad|
| ||Name||yes||(none)||Name of device, i.e. eth0.5 or vlan5|
| ||Parent interface||yes||(none)||Name of parent/base interface, i.e. eth0|
| ||VLAN Id||yes||(none)||VLAN Id|
| ||MAC||no||(none)||MAC of new interface|
Let's take the example of TP-Link outdoor CPE210 wireless adapter. It has only one NIC, like most outdoor devices, but it can be extended to support several virtual NICs very easily.
In the following example, eth0 is segmented into 2 VLAN-interfaces, with VLAN ID 106 and 204 using explicit manual configuration:
config device option type '8021q' option ifname 'eth0' option vid '106' option name 'vlan1' config device option type '8021q' option ifname 'eth0' option vid '204' option name 'vlan2' config interface 'lan' option type 'bridge' option ifname 'vlan1' option proto 'static' option ipaddr '192.168.1.1' option netmask '255.255.255.0' config interface 'wan' option ifname 'vlan2' option proto 'dhcp'
An equivalent configuration in implicit notation is shown below.
Note that the
device sections are missing and the VLAN ID and parent interface is derived from the
ifname option value in dot-notation.
config interface 'lan' option type 'bridge' option ifname 'eth0.106' option proto 'static' option ipaddr '192.168.1.1' option netmask '255.255.255.0' config interface 'wan' option ifname 'eth0.204' option proto 'dhcp'