Assume two hosts on a private network behind a NAT with IP a

Assume two hosts on a private network behind a NAT with IP address 192.168.1.4 and 192.168.1.7. They start a communication at the same time with TCP to an external (i.e., on a public network) web server 128.119.245.12 using port 80. The NAT has an internal address 192.168.1.1 and a (single) global address 149.164.33.254. Show the address and port fields (for both source and destination) of the two TCP SYN segments on the private network inside the NAT. Propose a NAT binding after the NAT has forwarded the two segments to the public network. Show the address and port fields (for both source and destination) of the two TCP SYN segments on the public network outside the NAT. The server replies with SYN/ACK to both requests. Show the address and port fields (for both source and destination) of the two TCP SYN/ACK segments inside and outside the NAT.

Solution

b) The two networks in our example will use a different /16 address block each carved from the private 192.168.1.1/8 address block. Each network is connected to the Internet by a gateway machine which has a private address in the specified range and a static public IP address.Your network will almost certainly be using a different IP range and structure and the examples below will need to be modified accordingly. If you are unfortunate enough that both networks are currently using the same IP range then one of them will have to be renumbered before they can be linked as addresses must be unique in any IP network.