>>А есть ли маршрут к ним? Все три подсети разные.
>есть
Советую принять во внимание (man 8 ipfw):
The fwd action does not change the contents of the packet at all. In particular, the destination address remains unmodified, so packets forwarded to another system will usually be rejected by that system unless there is a matching rule on that system to capture them.
А также вот что (там же):
If ipaddr is not a local address, then the port number (if specified) is ignored, and the packet will be forwarded to the remote address, using the route as found in the local routing table for that IP.