Internet Connectivity without BGP

The majority of ISP customers do not need, and do not use BGP.  For this arrangement, you create a default route towards your upstream provider, and all non- local packets go out the interface specified by the route.  Your provider typically configures static routes towards you on their side, redistributes those static routes into their IGP, and redistributes their IGP into BGP.  Some ISP’s have all of their BGP done statically.

Basically, if you have any address space "inside" of your provider's larger "netblock" or "aggregate", you won't be advertised to the outside world specifically – instead, your provider will simply advertise their larger block – which includes you. If you have any other networks (an old Class C; customers with address space; etc...) your provider will just statically announce those routes to the world and statically route them inside their network to your leased-line/ router interface(s). 

Let's review what happens when a customer is connected to the Internet without speaking BGP (Border Gateway Protocol) to their provider.  They will create a default route to the edge router, and all non- local packets go out the interface specified by the route.

Basically, since the customer will receive an address space "inside" of the Providers much larger address space, they won't be advertised to the outside world specifically – instead, the provider will just advertise our own larger block.