A NAT (Network Address Translation) works by modifying the IP address information in the headers of IP packets as they pass through a router or firewall. This process allows multiple devices on a private network to share a single public IP address for accessing external networks, such as the internet. When an internal device sends a packet to an external network, the NAT device changes the private IP address in the packet header to its own public IP address. When the response packet comes back, the NAT device translates the public IP address back to the appropriate private IP address of the originating device.
NAT actually works by maintaining a NAT table that keeps track of active connections and their corresponding translations between private and public IP addresses and ports. When a device on a private network initiates a connection to an external network, the NAT device records the private IP address and port number along with the corresponding public IP address and a new, unique port number. This mapping allows the NAT device to correctly route incoming response packets back to the originating device by looking up the entries in the NAT table.
NAT works with an example, such as when a computer on a private network with the IP address 192.168.1.2 wants to access a website. The computer sends a request to the NAT device, which assigns the request a public IP address, say 203.0.11, and a unique port number, like 40000. The NAT device records this mapping in its NAT table and forwards the request to the website’s server. When the server responds, the NAT device receives the response, checks its NAT table to find the corresponding private IP address and port, and then forwards the response back to the computer at 192.168.1.2.
The mechanism of NAT involves translating private IP addresses to a public IP address and vice versa, typically using a NAT table. The NAT table records the mappings of internal private IP addresses and ports to external public IP addresses and ports. The translation process allows devices within a private network to communicate with external networks using a single public IP address. NAT modifies the IP packet headers as they pass through the router, ensuring that response packets can be correctly routed back to the originating device.
NAT rules work by defining how IP address and port translations should be handled by the NAT device. These rules specify which private IP addresses and port ranges are to be translated to which public IP addresses and port ranges. When a packet matches a NAT rule, the NAT device applies the specified translation and updates the NAT table with the mapping information. NAT rules ensure that traffic flows are correctly managed and that responses are routed back to the appropriate internal devices. They are configured to handle various types of traffic, such as inbound and outbound connections, and can be customized to meet specific network requirements.