Plumb / Unplumb IP addresses on Linux/Solaris

ifconfig eth0:1 {ip-address} netmask 255.255.255.0
ifconfig eth0:1 down

Try these commands too..
ifconfig eth0 10.0.0.1 broadcast 172.x.x.x netmask 255.255.255.0 up
ifdown eth0
ifup eth0

To have the interfaces to come up on reboot automatically,
/etc/sysconfig/network

create files ifcfg-eth0 or fcfg-eth0:1
A sample file

DEVICE=eth0
BOOTPROTO=static
BROADCAST=
HWADDR=
IPADDR=
NETMASK=
NETWORK=
ONBOOT=yes
TYPE=Ethernet

Solaris
/sbin/ifconfig {interface (e.g bge0:30}down unplumb

/sbin/ifconfig {interface} plumb
/sbin/ifconfig {interface} {ip_addr} netmask {netmask_addr} broadcast {broadcast_addr} up

/etc/hostname.{interface}