I have just setup a m0n0wall box and am toying with it and have 
encountered an odd and seemingly inexplicable problem in filtered bridging 
mode. I have two hosts behind the m0n0wall and both pass traffic in and 
out fine. However, only one is being affected by the traffic rules, the 
other passess all traffic both directions. I can confirm the first host is 
affected by changing the rules and seeing the changes in port scans, but 
no change in rules has any affect on the other host. Both hosts are on a 
VLAN seperate from the Internet connection and so must be passing through 
the m0n0wall to get any traffic (confrimed by checking the config on the 
switch and by unplugging the m0n0wall).

Here is the setup:

The WAN interface on the monowall is set to x.x.x.107 with a /24 subnet 
and x.x.x.1 as it's default gateway. It is connected to VLAN 1 with the 
DSL connection to the ISP. The OPT1 interface is bridged to WAN, and 
filtering mode is enabled. The two hosts are x.x.x.11 and x.x.x.114. The 
hosts and OPT1 are connected to VLAN 2 and are the only devices on it. 
Host 11 is filtered fine, and all rules apply to it properly. Host 114 is 
not filtered at all, and all rules seem to have no affect.

I cannot figure out what the reason for this and would appreciate any 
insight. My only theory is that 11 is less than the m0n0wall's IP (107) 
and 114 is greater, though I fail to see why that would have any effect.

I appologise if this has been asked before, I couldn't find any reference 
to a problem like this in the docs or archives. I appreciate any help or 
insights you can give.

--Jesse