I think the issue is called double-natting and not sure if PT can do solution; after all it is only a simulator. the issue here is static NAT translation on ISP router. we have PC <>CE<>ISP<>Server. So, if your PC 192.168.1.10 pings 10.0.0.10. CE router adds entry to its NAT table and move out. entry is now translated to 220.110.0.2:x. ISP router does not have any nat configured on entry (serial interface), so it passes it w/o any translation. Ping gets to server who replies with source 10.0.0.10 and destination 220.110.0.2. Now, ISP translates this with ip nat inside source static 10.0.0.10 220.110.0.1, so 10.0.0.10 becomes 220.110.0.1, and destination is 220.110.0.2. CE router does not have NAT entry for this packet, look at show ip nat translations table. Packet is not process by NAT but it is checked by router ICMP process which says I did not initiate this and drops packet.
Regards, ML
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