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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.
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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.

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