ipfw get IP by DHCP on re0 (without rules allowing it)

#!/bin/sh
fwcmd="/sbin/ipfw -q"
RFC1918="10.0.0.0/8, 192.168.0.0/16, 172.16.0.0/12"
INTERNAL_LANS="10.1.2.96/27,10.1.3.24/29"
# re0: Interface facing Internet (get IP by DHCP)
# re1: LAN Internal interface
# wlan0: Wifi Internal interface
# tun0: OpenVPN tunnel
# Flush out the list before we begin.
${fwcmd} -f flush
# Didn't filter on loopback,internal interfaces and OpenVPN tunnel
${fwcmd} add pass ip from any to any via lo0
${fwcmd} add pass ip from any to any via lo1
${fwcmd} add pass ip from any to any via re1
${fwcmd} add pass ip from any to any via wlan0
${fwcmd} add pass ip from any to any via tun0
# Create a NAT table
${fwcmd} nat 123 config if re0 same_ports unreg_only reset
# Check incoming packets against NAT table
${fwcmd} add nat 123 ip from any to any in via re0
# Check incoming packets against statefull table
${fwcmd} add check-state
# Allow ICMP from myself
${fwcmd} add pass icmp from me to any out via re0 keep-state
# Allow DNS from myself
${fwcmd} add pass udp from me to any 53 out via re0 keep-state
# Allow NTP from myself
${fwcmd} add pass udp from me to any 123 out via re0 keep-state
# Allow OpenVPN from myself
${fwcmd} add pass udp from me to any 1195 out via re0 keep-state
# Never emit packets with RFC1918 destination on Internet (in case of tunnel down)
${fwcmd} add deny ip from any to ${RFC1918} out via re0
# NAT internal networks when they exit to Internet
${fwcmd} add nat 123 ip from ${LANS} to any out via re0

[manager@router]~> sudo ipfw -a l
ipfw: DEPRECATED: 'l' matched 'list' as a sub-string
00100   0     0 allow ip from any to any via lo0
00200   0     0 allow ip from any to any via lo1
00300   6   408 allow ip from any to any via re1
00400   6   408 allow ip from any to any via wlan0
00500  24  2284 allow ip from any to any via tun0
00600 134 15118 nat 123 ip from any to any in via re0
00700   0     0 check-state
00800   0     0 allow icmp from me to any out via re0 keep-state
00900   7   484 allow udp from me to any dst-port 53 out via re0 keep-state
01000  48  3648 allow udp from me to any dst-port 123 out via re0 keep-state
01100  86 10979 allow udp from me to any dst-port 1195 out via re0 keep-state
01200   0     0 deny ip from any to 10.0.0.0/8,192.168.0.0/16,172.16.0.0/12 out via re0
01300   0     0 nat 123 ip from 10.239.142.96/27,10.239.143.24/29 to any out via re0
65535   0     0 deny ip from any to any

[manager@router]~> sysrc ifconfig_re0
ifconfig_re0: DHCP
[manager@router]~> ifconfig re0
re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=8209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,LINKSTATE>
        ether 00:0d:b9:33:13:24
        inet6 fe80::20d:b9ff:fe33:1324%re0 prefixlen 64 scopeid 0x1
        inet 192.168.100.70 netmask 0xffffff00 broadcast 192.168.100.255
        nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
[manager@router]~> uname -a
FreeBSD olivier 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r275821M: Thu Dec 18 01:39:49 CET 2014     root@SM1.orange.bsdrp.net:/usr/obj/EINE.amd64/usr/local/BSDRP/EINE/FreeBSD/src/sys/amd64  amd64

=> How can it get an IP address by DHCP ?