1. Network Address Translation Sandip Chakraborty

2. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467

3. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 8123 DP:3467 SIP: 10.3.100.101 DIP:59.32.123.111

4. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 8123 DP:3467 SIP: 10.3.100.101 DIP:59.32.123.111 NAT Makes a mapping from the available public IP pool. Say, the NAT has available public IP pool 212.12.1.1 to 212.12.1.10

5. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 4598 DP:3467 SIP: 212.12.1.9 DIP:59.32.123.111 NAT makes the changes in the source IP and source port at IP and TCP headers of the packet

6. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 4598 DP:3467 SIP: 212.12.1.9 DIP:59.32.123.111

7. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 3467 DP:4598 SIP: 59.32.123.111 DIP:212.12.1.9 Now, Destination prepares the response packet by interchanging source IP and destination IP

8. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 3467 DP:4598 SIP: 59.32.123.111 DIP:212.12.1.9 The packet comes to NAT, as NAT has the IP 212.12.1.9

9. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 3467 DP:8123 SIP: 59.32.123.111 DIP:10.3.100.101 NAT makes inverse translation looking at the NAT table. Make changes at Destination IP and Port

10. NAT PRIVATE NETWORK PUBLIC NETWORK IP: 10.3.100.101 Port: 8123 IP: 10.3.100.112 Port: 9678 IP: 59.32.123.111 Port: 3467 SP: 3467 DP:8123 SIP: 59.32.123.111 DIP:10.3.100.101 Deliver the packet to proper destination in the private network