When booting with the standard rh kernel, the IP aliases get assigned.
When booting with a customized kernel where the ethernet card driver is
build into the kernel the "ifup eth0:0" command outputs

  SIOCSIFADDR: No such device
  SIOCSIFFLAGS: No such device
  SIOCSIFNETMASK: No such device
  SIOCSIFBRDADDR: No such device
  SIOCSIFFLAGS: No such device
  SIOCADDRT: No such device

and in the /var/log/messages file you find

Mar 15 11:59:42 gate modprobe: can't locate module eth0:0
Mar 15 11:59:42 gate last message repeated 4 times

or similar hints. The eth0 device is still up and modprobe tries to
reload the net driver again, obviously not recognizing that the driver
is built monolythic into the kernel.

Andreas J. Bathe <ajb>