[CentOS] more than one IP address on network device?

Sat Sep 3 17:34:37 UTC 2016
Walter H. <Walter.H at mathemainzel.info>

Hello

/etc/sysconfig/network-scripts/ifcfg-eth0 looks like this:

# Intel Corporation 82545EM Gigabit Ethernet Controller (Copper)
TYPE=Ethernet
NAME=eth0
NM_CONTROLLED=no
IPV4_FAILURE_FATAL=yes
UUID=cc2635ff-3c14-48ba-b19a-84c5b9d36a9d
ONBOOT=yes
DEVICE=eth0
BOOTPROTO=none
HWADDR=00:50:56:01:00:01
BROADCAST=192.168.0.255
IPADDR=192.168.0.10
NETMASK=255.255.255.0
NETWORK=192.168.0.0
GATEWAY=192.168.0.1
DNS1=192.168.0.1
DNS2=192.168.0.100
DOMAIN='domain.tld'
USERCTL=no
IPV6INIT=yes
IPV6ADDR=ipv6addr
IPV6_AUTOCONF=no
IPV6_DEFAULTGW=ipv6addr-gateway
IPV6_DEFAULTDEV=eth0

if I would need an additional IPv6 address I'd just add
IPV6ADDR_SECONDARIES="ipv6addr"
to this file; if I would need an additional IPv4 address this works only 
by a virtual device
e.g. eth0:1 like this:

/etc/sysconfig/network-scripts/ifcfg-eth0:1
# Intel Corporation 82545EM Gigabit Ethernet Controller (Copper), Alias 1
TYPE=Ethernet
DEVICE=eth0:1
ONPARENT=yes
BOOTPROTO=none
BROADCAST=192.168.0.255
IPADDR=192.168.0.17
NETMASK=255.255.255.0
NETWORK=192.168.0.0
GATEWAY=192.168.0.1
DNS1=192.168.0.1
DNS2=192.168.0.100

why can't I add this to the virtual device eth0:1,
if I needed both an additional IPv4 and an additional IPv6 address?
IPV6INIT=yes
IPV6ADDR=ipv6addr
IPV6_AUTOCONF=no
IPV6_DEFAULTGW=ipv6addr-gateway
IPV6_DEFAULTDEV=eth0:1


Thanks,
Walter