[gentoo-user] network drivers

[vetrocemento]

Hi guys.
why while in livecd mode my ethernet device (Ethernet controller: Broadcom 
Corporation 
NetXtreme BCM5751M Gigabit Ethernet PCI Express (rev 21) ) works perfectly out 
of the box, 
in dhcp mode, but after installing gentoo, system says ' network interface eth0 
does not exist'?
in kernel's .config file  (2.6.25) I choose to install the drivers for broadcom 
NetXtreme II and 
broadcom t3.there's something else I forgot to do?
 thanks in advance
                  Giacomo