Openbsd6.1 as firewall can access the internet but the LAN behind it cannot

[lu jian]

Hi

I have an i386 machine with two network interfaces, one of which connect to the 
uplink ISP via pppoe, the other connects to the WAN port of a wireless router 
to which all LAN machines and cell phones connect (via wifi).

The problem is that this i386 machine (which I intend as a firewall) can access 
the internet, but all LAN machines cannot.

Hint: my wireless router can obtain dhcp address from the i386 machine.

These two network interfaces on the i386 are bge0 and fxp0.

1) Configuration for fxp0:
    # cat /etc/hostname.fxp0
        up
    # cat /etc/hostname.pppoe0
        inet 0.0.0.0 255.255.255.255 NONE \
               pppoedev fxp0 authproto chap \
               authname 'account' authkey '123' up
         dest 0.0.0.1

!/sbin/route add default -if pppoe0 0.0.0.1

2) Configuration for bge0:
    # cat /etc/hostname.bge0
       inet 192.168.0.1 255.255.255.0 192.168.0.255

3) Configuration for dhcp:
     # vi /etc/rc.conf
         dhcp_flags=''

     # rcctl set dhcpd flags bge0

4) enable forwarding:
     # echo 'net.inet.ip.forwarding=1' >>/etc/sysctl.conf

What can I do for the LAN machines to access the internet. 

appreciate for any criticism on my ignorance (-;
Lujian