Consider the following scenario:
The customer wants to filter and allow only a default route from both ISPs, and prefer the circuit through AS 65100 as primary.
The filtering is accomplished using the ip prefix-list command, which is applied to both route map statements to limit the advertisements from the ISP to default routes only.
The AS Path access-list is only applied to the first permit statement of the route map. This is the mechanism which matches ISP1 and allows the customer to set a local preference of 150 to prefer it. The AS Path entry for ^65100$ indicates that the path should only have ISP1’s local AS in its path attribute – all others will not match.
Stuck-in-Active: Journal of an IT-Network Administrator 