NAT and PAT

NAT (Network Address Translation) and PAT (Port Address Translation) are techniques used to map public IP addresses to private IP addresses used in local networks. These techniques allow a single public IP address to be shared by multiple devices within a local network.

NAT is a one-to-one mapping technique that maps a public IP address to a single private IP address. NAT works by changing the source IP address of outgoing packets and the destination IP address of incoming packets. This allows devices with private IP addresses to access the internet using a single public IP address.

PAT, on the other hand, is a one-to-many mapping technique that maps multiple private IP addresses to a single public IP address. PAT works by using different port numbers to differentiate between the multiple devices sharing the same public IP address. When a packet is sent from a device with a private IP address to the internet, the source IP address is changed to the public IP address, and a unique port number is assigned to the packet. When a response is received from the internet, the destination IP address is changed to the private IP address and the port number is used to determine which device the packet should be sent to.

NAT and PAT are commonly used by home and small business networks to access the internet using a single public IP address. They provide a layer of security by hiding the private IP addresses of devices on the network from the internet. However, they can cause issues with certain applications that require unique public IP addresses or specific port numbers to function correctly.