Most home or small office networks have just one pathway out to the worldwide Internet, through a single Internet Service Provider. In that case, whenever any of your local computers wants to transmit a packet of IP information outside of your local subnet, it will need help from your router. Accordingly, your router serves as the - "Default Gateway" - to the Internet for your local network, and all of your local computers will need to know its local IP address. The DHCP protocol will work with your router's preprogrammed - "default" - behavior to automatically inform all of your other equipment of its local IP address. (Furthermore, - your router - will use your Internet Service Provider for - its - Default Gateway, and will learn the associated IP address through the DHCP protocol, from a DHCP server hosted by your ISP). If you are using the DHCP protocol everywhere, you should never need to specify a Default Gateway value.
