bridging in 2.1.2

[misteros2]

running redhat el5-3 as my host os with a local dhcp and tftp server

when starting a guest with a network 'host interface' and a coorect bootorder it starts a pxe request, the dhcp server got the request, gives the guest his ip address and point 'pxelinux.0' to my tftp server

the tftp server got the request but the guest starts retrying till the timeout

with vb version 2.0.6 it worked perfectly but the 'host interface' was configured to a 'vlan' and now with version 2.1.2 it points directly to my interface eth0 which put himself in promiscuous mode

any suggestions?