Doesn't work:

cat /etc/hostname.bnx0
up
cat /etc/hostname.vlan101
vlan 101 vlandev bnx0
inet 192.168.0.1 255.255.255.240 NONE

Works:

ifconfig eth1 up
vconfig eth1 add 101
ifconfig eth1.101 192.168.0.1 netmask 255.255.255.240