If you wish to enable dynamic addressing and automatically configure the ISP-facing interface using DHCP, observe the following (don’t forget to no shut the interface):
Note the DHCP server offers a default gateway that becomes a floating static route with AD of 254. This is default behavior and can be disabled on the local router (thereby removing the default route advertised by the ISP router) by issuing the following command:
no ip dhcp client request router
Stuck-in-Active: Journal of an IT-Network Administrator 