source: freewrt/package/busybox/files/vlan.pre-up

#!/bin/sh

case "$IFACE" in
        vlan0*)
                vconfig set_name_type VLAN_PLUS_VID
                VLANID=`echo $IFACE|sed "s/vlan0*//"`
                ;;
        vlan*)
                vconfig set_name_type VLAN_PLUS_VID_NO_PAD
                VLANID=`echo $IFACE|sed "s/vlan*//"`
                ;;
        eth*.0?*)
                vconfig set_name_type DEV_PLUS_VID
                VLANID=`echo $IFACE|sed "s/eth[0-9][0-9]*\.0*//g"`
                IF_VLAN_RAW_DEVICE=`echo $IFACE|sed "s/\(eth[0-9][0-9]*\)\..*/\1/"`
                ;;
        eth*.*)
                vconfig set_name_type DEV_PLUS_VID_NO_PAD
                VLANID=`echo $IFACE|sed "s/eth[0-9][0-9]*\.*//g"`
                IF_VLAN_RAW_DEVICE=`echo $IFACE|sed "s/\(eth[0-9][0-9]*\)\..*/\1/"`
                ;;
        *)      exit 0
                ;;
esac

if [ "$IF_VLAN_RAW_DEVICE" != "" ]
then
        [ -x /sbin/vconfig ] || exit 0
        if ! grep -q "$IF_VLAN_RAW_DEVICE" /proc/net/dev
        then
                echo "$IF_VLAN_RAW_DEVICE does not exist, unable to create $IFACE"
                exit 1
        fi

        ip link set up dev $IF_VLAN_RAW_DEVICE
        vconfig add $IF_VLAN_RAW_DEVICE $VLANID
        # change mac link layer address
        if [ "$IF_MAC_ADDRESS" != "" ]
        then
                ip link set $IF_VLAN_RAW_DEVICE.$VLANID address $IF_MAC_ADDRESS
        fi
        ip link set up dev $IF_VLAN_RAW_DEVICE.$VLANID
fi