Jeff, a technician, has been asked to add a subnet to the company's LAN. Which of the following interfaces on the router will be modified?

When adding a subnet to a company LAN, the FastEthernet 0/0 interface (or a subinterface of it) on the router is configured with the new subnet's gateway IP address. This LAN-facing interface connects the router to the internal switched network and must be updated to support routing for the new subnet.

The AUX 0 (auxiliary) port is used for out-of-band management, typically connecting a modem for remote console access, not for LAN subnet configuration.

The Console 0 port is a physical management interface used for direct local configuration and does not carry user data or subnet traffic.

The Serial 0/0/0 interface is typically used for WAN connections to an ISP or remote site and is not the appropriate interface for adding an internal LAN subnet.