ipfw: deny traffic between interfaces

[Eric Pretorious]

I'm using FreeBSD 4.10 as a masquerading firewall for three private networks 
and want to restrict traffic between each interface (kind of like VLAN's).

The firewall's interfaces are configured as such:

  sis0		public
  rl0			192.168.1.1
  fxp0		192.168.2.1
  sis1		192.168.4.1

...and ipfw is configured as such:

  00050	13453519	8660535275	divert 8668 ip from any to any via sis0
  00100	490			81262		allow ip from any to any via lo0
  00200	0			0			deny ip from any to 127.0.0.0/8
  00300	0			0			deny ip from 127.0.0.0/8 to any
  65000	26955802	17357286222	allow ip from any to any
  65535	0			0			deny ip from any to any

How can I accomplish this with ipfw? (I thought that something like `ipfw add 
400 deny ip from rl0 to not sis0` would do the job but it didn't.)

-- 
Eric P.,
Truckee, CA