Is a default gateway IP address necessary on a WAN interface for reaching destinations outside of the WAN subnet?

A default gateway IP address is essential on a WAN interface because it enables the device to route traffic to destinations outside of its local subnet. When a device needs to send data to an IP address that is not within its own subnet, it relies on the default gateway to forward that traffic. The default gateway acts as an intermediary device, typically a router, which knows how to reach external networks.

Without a properly configured default gateway, the device would not have a defined path for reaching IP addresses that are not on the same local network. Consequently, any outbound traffic destined for external networks would be discarded since the device wouldn't know where to send it. Thus, setting a default gateway is a fundamental requirement for ensuring connectivity beyond the WAN subnet, facilitating communication with external devices and services.