BigIron RX Series Configuration Guide 80953-1002253-01Filtering 26Configuring cooperative BGP4 route filteringBy default, the device performs all filtering of incoming routes locally, on the device itself. You canuse cooperative BGP4 route filtering to cause the filtering to be performed by a neighbor before itsends the routes to the device. Cooperative filtering conserves resources by eliminatingunnecessary route updates and filter processing. For example, the device can send a deny filter toits neighbor, which the neighbor uses to filter out updates before sending them to the device. Theneighbor saves the resources it would otherwise use to generate the route updates, and the devicesaves the resources it would use to filter out the routes.When you enable cooperative filtering, the device advertises this capability in its Open message tothe neighbor when initiating the neighbor session. The Open message also indicates whether thedevice is configured to send filters, receive filters or both, and the types of filters it can send orreceive. The device sends the filters as Outbound Route Filters (ORFs) in Route Refresh messages.To configure cooperative filtering, perform the following tasks on the device and on its BGP4neighbor:• Configure the filter.NOTEThe current release supports cooperative filtering only for filters configured using IP prefix lists.• Apply the filter as in inbound filter to the neighbor.• Enable the cooperative route filtering feature on the device. You can enable the device to sendORFs to the neighbor, to receive ORFs from the neighbor, or both. The neighbor uses the ORFsyou send as outbound filters when it sends routes to the device. Likewise, the device uses theORFs it receives from the neighbor as outbound filters when sending routes to the neighbor.• Reset the BGP4 neighbor session to send and receive ORFs.• Perform these steps on the other device.NOTEIf the device has inbound filters, the filters are still processed even if equivalent filters have beensent as ORFs to the neighbor.Enabling cooperative filteringTo configure cooperative filtering, enter commands such as the following.BigIron RX(config)# ip prefix-list Routesfrom1234 deny 20.20.0.0/24BigIron RX(config)# ip prefix-list Routesfrom1234 permit 0.0.0.0/0 le 32BigIron RX(config)# router bgpBigIron RX(config-bgp)# neighbor 1.2.3.4 prefix-list Routesfrom1234 inBigIron RX(config-bgp)# neighbor 1.2.3.4 capability orf prefixlist sendThe first two commands configure statements for the IP prefix list Routesfrom1234. The firstcommand configures a statement that denies routes to 20.20.20./24. The second commandconfigures a statement that permits all other routes. (Once you configure an IP prefix liststatement, all routes not explicitly permitted by statements in the prefix list are denied.)The next two commands change the CLI to the BGP4 configuration level, then apply the IP prefix listto neighbor 1.2.3.4. The last command enables the device to send the IP prefix list as an ORF toneighbor 1.2.3.4. When the device sends the IP prefix list to the neighbor, the neighbor filters outthe 20.20.0.x routes from its updates to the device. (This assumes that the neighbor also isconfigured for cooperative filtering.)
