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BGP prefixes advertisement to customer

I have connection to 4 upstream ISP: ISP1, ISP2, ISP3, ISP4. I have a customer (CUSTOMER1) with their own AS and BGP peering with me, they need only prefixes coming from ISP1. When I peer with them and create a route map to advertise to them only prefixes coming from ISP1, they don't get the full route only prefixes which is the best path is ISP1 (2000+ prefixes). In my router connected to ISP1 I see 125000+ prefixes. In my router most of the best path is ISP2/3/4. How can I advertise all the 125000+ prefixes coming from ISP1 to CUSTOMER1? Please give me some sample configuration or direct me to links to those samples. Thanks in advance


Re: BGP prefixes advertisement to customer

I'm not sure this is possible. BGP only advertises best paths and I'm not aware of a way to tell it to do otherwise. Best paths are stored in the so-called Loc-RIB -- this is the data structure from which advertised routes are taken from.


Re: BGP prefixes advertisement to customer

Looks like your customer needs to directly peer with ISP1.


New Member

Re: BGP prefixes advertisement to customer

Here's how I would do it. It's probably not best practice but it would work:

1. On the inetrface that faces your ISP1 customer, policy route his traffic to ISP1's next-hop.

2. In addition to the partial prefixes, configure your session to the customer with "default originate". This will send a default route in addition to the other prefixes.

3. If you are worried about creating a blackhole for your customer should the link to ISP1 fail, you can make your default route conditional by using a route map. Configure the following:

route-map conditional permit 10

match ip address 1

access-list 1 permit x.x.x.x x.x.x.x ( link between your router and ISP1)

neighbor x.x.x.x default-originate route-map conditional

This will only send the default to your customer if your ISP1 link is up.

Good luck !

New Member

Re: BGP prefixes advertisement to customer

I just realized I probably didn't answer your question very well. The only way to actualy send this guy a full table and ensure that he traverses ISP1 wpould be to:

1. Remove the AS filtering outbound and policy route him to ISP1

2. Figure out a way to configure a VRF for him so he can have his own private table.

Re: BGP prefixes advertisement to customer

Thanks to all your reply. I already have a solution. I filter the incoming route from ISP1 and put a weight on it, the other ISP I use local preference. I move all the other customer to router 2 so that they see the other ISP as best path and only see 2k best path thru ISP1. I