pf nat with pool addresses

[h bagade]

Hi all,

I am trying to use pf nat rules with pool support on FreeBsd 8.0, working
together with ipfw as the main firewall. According to the natting concepts i
faced in manuals and docs, nat concept is to map the source address to the
natted address when sending the packets from that source and then map the
destination address of the related reply packets.

but when I define pf nat rules with a pool of IP addresses not available on
the outside interface ip addresses, the outgoing traffic is natted to one of
the pool addresses but the response is not received via that interface so
the pf can map the destination address to the real one. here is one of my
configs i used during my tests:

*configurations:*
*pf.conf:*
nat on eth1 from { 11.11.11.0/24} to any ->
{172.16.10.1,172.16.10.2,172.16.10.3,172.16.10.4,172.16.10.5,172.16.10.6,172.16.10.7,172.16.10.8,172.16.10.9,172.16.10.10}

main system configurations:
eth0: 11.11.11.1
eth1: 172.16.10.64

system A: directly connected to eth0- 11.11.11.11
system B: directly connected to eth1- 172.16.10.65

in this configs the dafult route of system A and system B are the middle
systems connected ip address.

as mentioned, when systemA pings systemB, the ping requests are natted to
172.16.10.1 and received at systemB but systemB doesn't send icmp replies
because it doesn't know to whom it should send the replies (no answer to
system B 's ARP requests about who has the natted IP).

now my question is, isn't it the pf nat responsibilty to manage this
condition and send the ARP replies to SystemB?
or, are my configs wrong?
or i misunderstood the nat concepts?

any ideas or helps are really appriciated as i have to set this nat on my
main system, asap.
Thanks in advance.