- Move back to the IP mode: The rt1's interface that is connected to the Internet has received an IP address, which has been assigned by the ISP to which it is connected.
- Send a ping from st1 to the "172.12.0.3" address (corresponding to the address of the www server connected to the Internet): rt1 cannot reach the host.
- Add a line in rt1's routing table, as illustrated bellow.
- Once again, try to send the same ping request: the reply cannot be transported since the Internet does not recognize st1.
- Try to carry out this ping from rt1: everything works correctly.
- Move to the Transport mode.
- Send the request below from st1: it is accepted by the www server.
- Select "Reply a request" in www’s pop-up menu, and reply to st1: the reply cannot be transported.
- Select "IP configuration" in rt1’s pop-up menu, and set this router so as to activate the Nat/Pat translation, as illustrated below.
- Repeat the two preceding operations, i.e the sending of the request from st1, and the www reply: everything works correctly (you can repeat the operation in the step-by-step mode to watch the translation of address and port carried out by the router).
- st4, whose address is 11.0.0.2, also listens to port 80. Make sure it does.
- Try to send a TCP request on this port from st1 to st4: it cannot be transported.
- Send the same request from st1, but this time to rt2's address, i.e 172.12.0.4: the request can be transported, but it is refused because the router does not listen to the port.
- Activate the Nat/Pat translation on rt2 like, as illustrated below.
- Choose "Tables", and "Nat/Pat table" in rt2’s pop-up menu, and add the line illustrated below.
- Send a TCP request on port 80 from st1 to the following router's address: 172.12.0.4. The router transmits the request to the st4 server. Note: You could also have changed the port listened by st4.
- Answer this request from st4: everything works correctly.