VLAN
Related articles
Virtual LANs give you the ability to sub-divide a LAN. Linux can accept VLAN tagged traffic and presents each VLAN ID as a different network interface (eg: eth0.100
for VLAN ID 100
)
This article explains how to configure a VLAN using iproute2 and systemd-networkd or netctl.
Contents
Configuration
Previously Arch Linux used the vconfig
command to setup VLANs. This had been superseded by the ip
command. Make sure you have iproute2 installed.
In the following examples, lets assume the interface is eth0
, the assigned name is eth0.100
and the vlan id is 100
.
Create the VLAN device
Add the VLAN with the following command:
# ip link add link eth0 name eth0.100 type vlan id 100
Run ip link
to confirm that it has been created.
This interface behaves like a normal interface. All traffic routed to it will go through the master interface (in this example, eth0
) but with a VLAN tag. Only VLAN aware devices can accept them if configured correctly else the traffic is dropped.
Using a name like eth0.100
is just convention and not enforced; you can alternatively use eth0_100
or something descriptive like IPTV
. To see the VLAN ID on an interface, in case you used an unconventional name:
# ip -d link show eth0.100
The -d
flag shows full details on an interface:
# ip -d addr show 4: eno1.100@eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default link/ether 96:4a:9c:84:36:51 brd ff:ff:ff:ff:ff:ff promiscuity 0 vlan protocol 802.1Q id 100 <REORDER_HDR> inet6 fe80::944a:9cff:fe84:3651/64 scope link valid_lft forever preferred_lft forever
Add an IP
Now add an IPv4 address to the just created vlan link, and activate the link:
# ip addr add 192.168.100.1/24 brd 192.168.100.255 dev eth0.100 # ip link set dev eth0.100 up
Turning down the device
To cleanly shutdown the setting before you remove the link, you can do:
# ip link set dev eth0.100 down
Removing the device
Removing a VLAN interface is significantly less convoluted
# ip link delete eth0.100
Starting at boot
systemd-networkd
Use the following configuration files:
/etc/systemd/network/eno1.network
[Match] Name=eno1 [Network] DHCP=ipv4 VLAN=eno1.100 VLAN=eno1.200
/etc/systemd/network/eno1.100.netdev
[NetDev] Name=eno1.100 Kind=vlan [VLAN] Id=100
/etc/systemd/network/eno1.200.netdev
[NetDev] Name=eno1.200 Kind=vlan [VLAN] Id=200
Then enable systemd-networkd.service
. See systemd-networkd for details.
netctl
You can use netctl for this purpose, see the self-explanatory example profiles in /etc/netctl/examples/vlan-{dhcp,static}
.
Troubleshooting
udev renames the virtual devices
An annoyance is that udev may try to rename virtual devices as they are added, thus ignoring the name configured for them (in this case eth0.100
).
For instance, if the following commands are issued:
# ip link add link eth0 name eth0.100 type vlan id 100 # ip link show
This could generate the following output:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000 link/ether aa:bb:cc:dd:ee:ff brd ff:ff:ff:ff:ff:ff 3: rename1@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state DOWN link/ether aa:bb:cc:dd:ee:ff brd ff:ff:ff:ff:ff:ff
udev has ignored the configured virtual interface name eth0.100
and autonamed it rename1.
The solution is to edit /etc/udev/rules.d/network_persistent.rules
and append DRIVERS=="?*" to the end of the physical interface's configuration line.
For example, for the interface aa:bb:cc:dd:ee:ff (eth0):
/etc/udev/rules.d/network_persistent.rules
SUBSYSTEM=="net", ATTR{address}=="aa:bb:cc:dd:ee:ff", NAME="eth0", DRIVERS=="?*"
A reboot should mean that VLANs configure correctly with the names assigned to them.