Aliases can also be done by setting up some variables in your rc.conf
like:

ifaliases_ex0="192.168.192.88 255.255.255.0 192.168.192.89 255.255.255.0 192.168.192.90 255.255.255.0"

Or you can use /etc/ifaliases. For example:

192.168.192.88 ex0 255.255.255.0
192.168.192.89 ex0 255.255.255.0
192.168.192.90 ex0 255.255.255.0

But /etc/rc.d/network says these two ideas above are not recommended.

Have a look at documentation within the /etc/rc.d/network script and in
the rc.conf manual page.

   Jeremy C. Reed
   http://bsd.reedmedia.net/