BGP is an extremely complex protocol used throughout the Internet and within multinational organizations. Its main purpose is to connect very large networks or autonomous systems.
In many cases, the routing policy that is implemented in an AS is consistent with the policy for the ISP. In these cases, it is not necessary or even desirable, to use BGP to exchange routing information with the ISP. Instead, connectivity can be achieved through a combination of static routes and default routes.
Do not use BGP within the AS in the following situations:
1. There is only a single connection to the Internet or other AS.
2. Internet routing policy and route selection are not of concern to the AS.
3. The BGP routers have insufficient RAM or processor power to handle constant updates.
4. There is limited understanding of route filtering and the BGP path selection process.
5. Low bandwidth link between autonomous systems