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Example: ISP Network Case Study
This section provides an example of how policies
might be used in a typical Internet service provider (ISP) network.
In this network example (see Figure 11), the
ISP’s AS number is 1000. The ISP has two transit peers (AS 11111
and AS 22222) to which it connects at an exchange point. The ISP is
also connected to two private peers (AS 7000 and AS 8000) with which
it exchanges specific customer routes. The ISP has two customers (AS
1234 and AS 2468) to which it connects using the BGP protocol.
Figure 11: ISP Network Example
In this example, the ISP policies are configured
in an outbound direction; that is, the example focuses on the routes
that the ISP announces to its peers and customers, and includes the
following:
- The ISP has been assigned AS 1000 and the routing space
of 192.168.0/17. With the exception of the two customer networks
shown in Figure 11, all other customer routes
are simulated with static routes.
- The ISP has connectivity to two different exchange peers:
AS 11111 and
AS 22222. These peers are used for transit
service to other portions of the Internet. This means that the ISP
is accepting all routes (the full Internet routing table) from those
BGP peers. To help maintain an optimized Internet routing table, the
ISP is configured to advertise only two aggregate routes to the transit
peers.
- The ISP also has direct connectivity to two private peers:
AS 7000 and AS 8000. The ISP administrators want all data to the private
peers to use this direct link. As a result, all the customer routes
from the ISP are advertised to those private peers. These peers then
advertise all their customer routes to the ISP.
- Finally, the ISP has two customers with which it communicates
using BGP:
AS 1234 and AS 2468. Each customer has
a different set of requirements.
The following sections discuss the following topics:
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