The NAT box you design is implemented and will soon be used to provide IP address sharing for users of cable modems and DSL service. During the testing though, it becomes obvious that port mapping is not the only capability that is required for a NAT box. For example, some ICMP diagnostics do not work when the packets are sent through your box. Explain in detail what is happening, and what changes must be made to the various packet headers by your software so that the packets flow properly across the NAT box. Given what you have learned, describe any limitations you might expect with your implementation. Be specific.