Which device is responsible for implementing network address translation (NAT)?

The device responsible for implementing network address translation (NAT) is the router. NAT is a technique that allows a router to translate private IP addresses within a local network to a single public IP address before data packets are sent out to the internet. This process helps conserve the number of public IP addresses used and adds a layer of security by keeping internal IP addresses hidden from external networks.

Routers are designed to manage network traffic and have the capability to distinguish between incoming and outgoing traffic. By using NAT, routers help devices on a local network communicate with external networks while maintaining a coherent address structure on the internal network. This function is especially important in environments where multiple devices need access to the internet but only have a limited number of public IP addresses available.

In contrast, a modem connects a local network to the internet but does not perform NAT. A network interface card (NIC) is used for connecting a device to a network and does not handle address translations. A switch operates at the data link layer and is used to connect devices within a local network but does not perform NAT or any form of address translation. Therefore, the router is the key device for implementing NAT in network communications.