Why don't you just tag your exportable routes and let them through, while blocking everything else? You could then build a route-map that places that tag on all of your inbound BGP customers. This would allow you to export everything that they send you (allowing them to send the more specific as Dorian stated) and use a static tag for your aggregate routes. Then all the more specific routes on your backbone would be filtered, unless it originated from a BGP customer - who would need to send the more specific advertisements to each of it's providers and allow routing to work correctly. I know, that's what we do! If you don't have the right tag, you don't get off! And I don't have to mess with any filters after they are set up. Barry

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You can remove the specifics at the edges of your network either via community based filtering or prefix based filtering. The former is much more flexible and is the one I'd recommend.

-dorian

I'd think prefix based filters would be more likely to be correct. Since you have to explicitly list what you think you should be announcing you protect against having routes you don't expect in your tables and against having interactions that cause unexpected routes to get tagged as announceable.

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-Chris (cgarner@sni.net)