VLAN

This article shows how to configure a network interface as an IEEE 802.1q VLAN trunk.

Installation

First, install the vlan package. This will give you support for VLANs in the /etc/network/interfaces file.

apk add vlan

Configuration

Edit the /etc/network/interfaces file:

auto eth0.8
iface eth0.8 inet static
	address 192.168.0.2
	netmask 255.255.255.0
	gateway 192.168.0.1
	vlan-raw-device eth0
	vlan_id 8

With the vlan package installed, ifup will find the trailing .8 in eth0.8 and will create a VLAN interface with vid 8 over eth0.

Alternatively with vlan8 over eth0:

auto vlan8
iface vlan8 inet static
	address 192.168.0.2
	netmask 255.255.255.0
	gateway 192.168.0.1
	vlan-raw-device eth0

A static IP address was used in the examples shown above, but DHCP can be used as well.

Example with bridges associated with VLANs over bonding with differing MTUs on the various VLANs

This serves as an example of some of the more complicated networking possible. Particularly, this would work well for a hypervisor attached to a dedicated storage VLAN. Less complicated implementations can be achieved by merely removing the non-applicable parts.

auto lo
iface lo inet loopback

auto bond0
  iface bond0 inet manual
  bond_slaves eth0 eth1
  bond_mode 802.3ad
  bond_miimon 100
  bond_xmit_hash_policy layer2+3
  post-up ip link set dev bondi0 mtu 9000

iface bond0.1

auto br1
iface br1
  address 192.168.1.196/24
  gateway 192.168.1.1
  bridge_ports bond0.1
  bridge_stp off
  bridge_fd 0.0
  post-up ip link set dev bond0.1 mtu 1500

iface bond0.10 inet manual

auto br10
  iface br10 inet static
  address 192.168.10.1/24
  bridge_ports bond0.10
  bridge_stp off
  bridge_fd 0.0

Example with two interfaces on the same adapter. One with VLAN and one without

Since Linux doesn't allow multiple default gateways we need to use a second routing table using iproute2

apk add iproute2

Then we'll add two new routing tables to the config file. One for each network

echo "1 rt1" >> /etc/iproute2/rt_tables;echo "2 rt2" >> /etc/iproute2/rt_tables;

Now we need to edit /etc/network/interfaces

auto lo
iface lo inet loopback

# the native interface without a VLAN (also called untagged)

auto eth0
iface eth0
        address 192.168.1.100/24
        gateway 192.168.1.1
        post-up ip route add 192.168.1.0/24 dev eth0 src 192.168.1.100 table rt1
        post-up ip route add default via 192.168.1.1 dev eth0 table rt1 # the actual gateway for this interface
        post-up ip rule add from 192.168.1.100/32 table rt1
        post-up ip rule add to 192.168.1.100/32 table rt1

# second interface with the vlan tag 5
auto eth0.5
iface eth0.5
    address 192.168.5.100/24
    post-up ip route add 192.168.5.0/24 dev eth0.5 src 192.168.5.100 table rt2
    post-up ip route add default via 192.168.5.1 dev eth0.5 table rt2 # the actual gateway for this interface
    post-up ip rule add from 192.168.5.100/32 table rt2
    post-up ip rule add to 192.168.5.100/32 table rt2

Note that if you want to add a third interface this way, you'll have to add another routing table