Using the previous configuration, the figures illustrate the dynamic NAT translation process between two clients and the web server:
In Figure 1, the traffic flow from inside to outside is shown:
1. The hosts with the source IPv4 addresses (192.168.10.10 (PC1) and 192.168.11.10 (PC2)) send packets requesting a connection to the server at the public IPv4 address (220.127.116.11).
2. R2 receives the first packet from host 192.168.10.10. Because this packet was received on an interface configured as an inside NAT interface, R2 checks the NAT configuration to determine if this packet should be translated. The ACL permits this packet, so R2 will translate the packet. R2 checks its NAT table. Because there is no translation entry for this IP address, R2 determines that the source address 192.168.10.10 must be translated dynamically. R2 selects an available global address from the dynamic address pool and creates a translation entry, 18.104.22.168. The original source IPv4 address (192.168.10.10) is the inside local address and the translated address is the inside global address (22.214.171.124) in the NAT table.
For the second host, 192.168.11.10, R2 repeats the procedure, selects the next available global address from the dynamic address pool, and creates a second translation entry, 126.96.36.199.
3. R2 replaces the inside local source address of PC1, 192.168.10.10, with the translated inside global address of 188.8.131.52 and forwards the packet. The same process occurs for the packet from PC2 using the translated address for PC2 (184.108.40.206).
In Figure 2, the traffic flow from outside to inside is shown:
4. The server receives the packet from PC1 and responds using the IPv4 destination address of 220.127.116.11. When the server receives the second packet, it responds to PC2 using the IPv4 destination address of 18.104.22.168.
5a. When R2 receives the packet with the destination IPv4 address of 22.214.171.124; it performs a NAT table lookup. Using the mapping from the table, R2 translates the address back to the inside local address (192.168.10.10) and forwards the packet toward PC1.
5b. When R2 receives the packet with the destination IPv4 address of 126.96.36.199; it performs a NAT table lookup. Using the mapping from the table, R2 translates the address back to the inside local address (192.168.11.10) and forwards the packet toward PC2.
6. PC1 at 192.168.10.10 and PC2 at 192.168.11.10 receive the packets and continue the conversation. The router performs Steps 2 to 5 for each packet. (Step 6 is not shown in the figures.)