Dell BigIron RX Series, Configuration Manual

Page: 885 / 1458

BigIron RX Series Configuration Guide 809
53-1002253-01
Filtering
26
Configuring cooperative BGP4 route filtering
By default, the device performs all filtering of incoming routes locally, on the device itself. You can
use cooperative BGP4 route filtering to cause the filtering to be performed by a neighbor before it
sends the routes to the device. Cooperative filtering conserves resources by eliminating
unnecessary route updates and filter processing. For example, the device can send a deny filter to
its neighbor, which the neighbor uses to filter out updates before sending them to the device. The
neighbor saves the resources it would otherwise use to generate the route updates, and the device
saves the resources it would use to filter out the routes.
When you enable cooperative filtering, the device advertises this capability in its Open message to
the neighbor when initiating the neighbor session. The Open message also indicates whether the
device is configured to send filters, receive filters or both, and the types of filters it can send or
receive. 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 BGP4
neighbor:
•
Configure the filter.
NOTE
The 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 send
ORFs to the neighbor, to receive ORFs from the neighbor, or both. The neighbor uses the ORFs
you send as outbound filters when it sends routes to the device. Likewise, the device uses the
ORFs 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.
NOTE
If the device has inbound filters, the filters are still processed even if equivalent filters have been
sent as ORFs to the neighbor.
Enabling cooperative filtering
To configure cooperative filtering, enter commands such as the following.
BigIron RX(config)# ip prefix-list Routesfrom1234 deny 20.20.0.0/24
BigIron RX(config)# ip prefix-list Routesfrom1234 permit 0.0.0.0/0 le 32
BigIron RX(config)# router bgp
BigIron RX(config-bgp)# neighbor 1.2.3.4 prefix-list Routesfrom1234 in
BigIron RX(config-bgp)# neighbor 1.2.3.4 capability orf prefixlist send
The first two commands configure statements for the IP prefix list Routesfrom1234. The first
command configures a statement that denies routes to 20.20.20./24. The second command
configures a statement that permits all other routes. (Once you configure an IP prefix list
statement, 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 list
to neighbor 1.2.3.4. The last command enables the device to send the IP prefix list as an ORF to
neighbor 1.2.3.4. When the device sends the IP prefix list to the neighbor, the neighbor filters out
the 20.20.0.x routes from its updates to the device. (This assumes that the neighbor also is
configured for cooperative filtering.)