Content

| 9.1 |  | Autonomous Systems |
| 9.1.5 |  | When not to use BGP |

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:

- There is only a single connection to the Internet or other AS.
- Internet routing policy and route selection are not of concern to the AS.
- The BGP routers have insufficient RAM or processor power to handle constant updates.
- There is limited understanding of route filtering and the BGP path selection process.
- Low bandwidth link between autonomous systems

In Figure , router A is advertising a default network into the AS through a local IGP, such as RIP. A static route affords connectivity through router B to the AS for the ISP. The ISP is running BGP and is recognized by other BGP routers in the Internet.

> Note: In general, when there are different policy requirements than the ISP, it is necessary to use BGP to connect to an ISP.

| Interactive Media Activity Point and Click: When to use BGP and when not to use BGP Upon completion of this activity, the student will be able to decide when to use BGP and when not to use BGP.