6. Peer-to-peer connections by proxy (18 pts) As discussed in class, when two computers behind NATs want to communicate, they need an intermediate computer with a public IP address to help out. Here we will diagram and show why this is. 1. Using the same conventions as in the last problem, diagram a network in which there are two LANs, A and B, (situated behind separate NATS). Each contains two computers. Both LANs assign private IP addresses in the range of 192.168.1.X. The gateways for each NAT have public IP addresses. In LAN A, there is a machine S; in LAN B, there is a machine T. Produce the diagram, complete with IP addresses for all machines. 2. Machine S wants to send a packet to T (using source port 90 to destination port 100). Explain, conceptually, how this would be attempted and explain why this will fail. (4 pts) 3. Now introduce a new machine, X, on the public internet with a public IP address. Assign it a public IP address. Redraw the diagram. 4. Machine S now sends the data to X that it wants delivered to T. Assume that X runs a service on port 202 that will happily accept such data, store it, and attempt to deliver it. Show the packet headers for the data that S sends to X (for eventual delivery to T). Note that you don't need to show the data itself. Also, assume that X somehow knows miraculously that s wants the data to be delivered to T (on port 100). 5. Explain why machine X is still unable to deliver the data to machine T. 6. Now machine T starts polling server X - this means that it starts contacting the service on port 202 at regular time intervals (let's say every second). Explain how this enables machine X to deliver the data that S originally sent it for T