|  | 11.3 | Advanced ARP Concepts
| 11.3.1 | Default gateway

In order for a device to communicate with another device on another network, you must supply it with a default gateway. A default gateway is the IP address of the interface on the router that connects to the network segment on which the source host is located. The default gateway’s IP address must be in the same network segment as the source host.

If no default gateway is defined, communication is possible only on the device’s own logical network segment. The computer that sends the data does a comparison between the IP address of the destination and its own ARP table. If it finds no match, it must have a default IP address to use. Without a default gateway, the source computer has no destination MAC address, and the message is undeliverable.