How is it possible that NAT doesn't back translate packets?

I have the following topology and from myhost I can ping router2 but can't ping router1. With tcpdump I can observe how my pings go and I see that both router1 and router2 reply. But only replies from router2 are appearing in re2. I.e. NAT back translation doesn't work. Any other traffic also doesn't return. Is it possible to diagnose the situation, may be with ipfw command? Is it possible to see firewall logs in realtime and discover if it blocks the traffic? # Details ## Experiment 1 myhost> ping router1 pfSense> tcpdump -n -i re1 icmp pfSense> tcpdump -n -i re2 icmp ## Experiment 2 myhost> ping router2 pfSense> tcpdump -n -i re3 icmp pfSense> tcpdump -n -i re2 icmp *** # Update 2 I have 3 ISPs: behind re0, re1 and re3. ISPs behind re1 and re3 uses their own modems (router1 and router2 on the diagram) and ISP behind re0 is plain twisted pair. re2 is LAN Routing table > netstat -nr -f inet default 192.168.100.1 UGS re3 link#1 UHS re0 link#1 UHS re0 .0/23 link#1 U re0 .151 link#7 UHS lo0 127.0.0.1 link#7 UH lo0 192.168.0.0/24 link#2 U re1 192.168.0.2 link#7 UHS lo0 192.168.10.0/24 link#3 U re2 192.168.10.1 link#7 UHS lo0 192.168.17.0/24 link#11 U ovpns1 192.168.17.1 link#7 UHS lo0 192.168.18.0/24 link#12 U ovpns2 192.168.18.1 link#7 UHS lo0 192.168.19.0/24 link#13 U ovpns3 192.168.19.1 link#7 UHS lo0 192.168.27.0/24 link#14 U ovpns4 192.168.27.1 link#7 UHS lo0 192.168.29.0/24 link#15 U ovpns5 192.168.29.1 link#7 UHS lo0 192.168.100.0/24 link#4 U re3 192.168.100.2 link#7 UHS lo0