When I add an IPv4 address for the interface eth0:0 with ifconfig, it is created correctly:

ifconfig eth0:0 add 192.168.10.10

This can be verified by ifconfig or "ip a".

When I add an IPv6 address however, ifconfig seems to ignore the alias of the interface:

ifconfig eth0:0 add fc00::2/48

The address fc00::2/48 is added to eth0 then, not to eth0:0, no matter if eth0:0 previously exists with an IPv4 address or not.

I'm doing this on CentOS 5 but I guess it is a general behaviour of ifconfig? Am I doing something wrong or is this by intention? I'm using separate aliases for interfaces very often and I hoped to use it for IPv6 as well.

Kind regards Marten