Network Address Translation (NAT) Overview The objective of this exercise is to analyze how NAT translations occur on a network. Objectives for this activity are to: Understand the purpose of NAT Examine your network settings Part 1 An Overloaded NAT Topology - Consider the following NAT topology that may be very similar to your own home network with a private and public network connected through a NAT router. You have multiple devices on your inside/private network and they are all sharing a single outside/public IP address that is most likely assigned by your ISP. This would be called NAT overloading. In the diagram below, the outside public IP address is on the 10.100.100.0 network only for the sake of the example. In reality, this would be an IP address that your ISP (cable modem, DSL, etc.) assigns to your device. Inside/Private Network Inside Private NAT IP: 192.168.1.1 PC 1/4 192.168.1.10 PC 2/5 192.168.1.11 NAT Router Outside/Public Network Outside NAT Public IP: 10.100.100.1 PC 3/6 10.100.100.2 Part 1 Questions - An Overloaded NAT Topology Please use complete sentences when writing your answers. 1. (10 pts) What is the purpose of NAT? Hint: Think about what problem NAT solves and why it is used in a network. 2. (10 pts) What is a private network? 3. (10 pts) What is a public network? 4. (10 pts) Consider the topology above. What would you set as the default gateway for PCs 1/4 and 2/5? 5. (10 pts) In the above topology, the NAT configuration is setup to overload with the external IP assigned to the NAT box. Consider that PC1 pings PC3. Diagram what the ICMP echo request will look like on the inside network. Include the ICMP message, the IP packet and the ethernet frame. 6. (10 pts) What will that same ICMP echo request look like on the outside network? Diagram the message, again including the ICMP message, the IP packet and the ethernet frame. 7. (10 pts) Diagram what the echo reply for this exchange will look like on the outside network. 8. (10 pts) Diagram what the echo reply for this exchange will look like on the inside network. 9. (20 pts) Diagram what the NAT translation table will look like on the NAT box (NAT function resides in the router) .