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I would like to know if it's possible to prevent some BGP prefixes from entering the RIB.

I'm receiving full internet routes from 2 ISPs, and I'm getting duplicate paths in BGP table, but only the best goes to the RIB. However, my routers have a limitation on the number of routes allowed in the RIB, and I would like to prevent some BGP routes from entering the RIB (more specifically, the ones that are tied, so that the router just uses the default route).

I know all kind of filtering can be done to prevent routes from entering the BGP table, but is it possible to use route-maps to do what I want? Where would I apply them? Thanks!

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  • I know the redistribute commands on Cisco CLI, there you can "put" routes from bgp to rip, shouldn't be much different on different IOS. Also a part of your configuration and what device you use would be helpful.
    – Eggi
    Sep 5 '16 at 9:31
  • When you redistribute between 2 routing protocols you can always filter using a route-map. But you never redistribute from the BGP table to the RIB, and you don't even enter a command for that, the best routes are simply installed automatically. What I am trying to know is if there s any way of filtering these best routes, the way I would do in a redistribution. Note: These devices are Brocade, which configurations are very Cisco-like.
    – user30260
    Sep 5 '16 at 9:33
  • Ok, forget the retribution, read RIP not RIB. One thing i can think of is using the neighbor command. example: neighbor {ip-address| peer-group-name} remote-as autonomous-system-number neighbor {ip-address| peer-group-name} route-map map-name {in | out} and configure your route map for the ip adresses you want to route.
    – Eggi
    Sep 5 '16 at 9:42
  • cisco site link Uses the distribute command in the router bgp config. Try this.
    – Eggi
    Sep 5 '16 at 9:47
  • Hope you also have a default route if you do this
    – user88975
    Sep 6 '16 at 12:51
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You may filter same way as you would filter bogon networks with prefix lists. For example:

ip prefix-list rfc1918 deny 10.0.0.0/8 le 32

router bgp xxx
 neighbor x.x.x.x prefix-list rfc1918 in

But routers with full BGP feeds should avoid default routes.

Other ways to filter incoming prefixes is to use distribute lists with access-lists.

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  • Thank you, but you missed the point. You are still filtering BGP prefixes from entering BGP table. I want to allow all prefixes INTO the BGP table, from both ISPs. I then want to filter WHAT GOES INTO the RIB. Assuming that is possible.
    – user30260
    Sep 5 '16 at 11:25
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I found what I was looking for. It is possible to filter BGP routes from entering the RIB. You just have to use the table-map command to filter using a route-map. http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/bgp-selective_route_download.pdf

Thanks anyway.

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