How to configure DHCP client on a bridge ?

Hi,

I'm trying to follow the advice fount in the handbook by configuring
the IP address on the bridge0 interface rather than on a member
interface.
Then I've configured my rc.conf like that:

cloned_interfaces="bridge0"
ifconfig_bridge0="addm bge0 addm xl0 DHCP"
ifconfig_bge0="up"
ifconfig_xl0="up"

But, with this configuration, the dhclient didn't start automatically
on the bridge0 interface.
After a reboot, my bridge0 status is:
[olivier_at_d630]~>ifconfig bridge0
bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	ether 82:03:c8:73:85:cc
	id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
	maxage 20 holdcnt 6 proto rstp maxaddr 100 timeout 1200
	root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
	member: xl0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
	        ifmaxaddr 0 port 5 priority 128 path cost 55
	member: bge0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
	        ifmaxaddr 0 port 2 priority 128 path cost 55

I need to manually start the dhclient on the bridge0 for getting my IP address:

[root_at_d630]~#dhclient bridge0
DHCPREQUEST on bridge0 to 255.255.255.255 port 67
DHCPNAK from 192.168.100.254
DHCPDISCOVER on bridge0 to 255.255.255.255 port 67 interval 6
DHCPOFFER from 192.168.100.254
DHCPREQUEST on bridge0 to 255.255.255.255 port 67
DHCPACK from 192.168.100.254
bound to 192.168.100.58 -- renewal in 432000 seconds.

I'm ussing current:
[root_at_d630]~#uname -a
FreeBSD d630.freenas.org 8.0-CURRENT FreeBSD 8.0-CURRENT #14: Thu Mar
12 14:17:22 CET 2009
root_at_d630.freenas.org:/usr/obj/usr/src/sys/DellD630  amd64

What is the good rc.conf parameters for using a dhclient on a bridge interface ?

Thanks,

Olivier