© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-1 Route Selection Using Policy Controls Using Outbound Route Filtering

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-2 Outline Overview Outbound Route Filtering BGP Prefix-Based Outbound Route Filtering Outbound Route Filter Message Configuring Outbound Route Filtering Using Outbound Route Filtering Monitoring Outbound Route Filtering Summary

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-3 Outbound Route Filtering The purpose of outbound route filtering is to reduce the amount of BGP traffic and CPU use needed to process routing updates. Routers exchange inbound filter configurations, which are used as outbound filters on neighboring routers. Filters are described in ORF entries. ORF entries are part of the route refresh message.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-4 Inbound vs. Outbound Filtering

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-5 BGP Prefix-Based Outbound Route Filtering Uses BGP ORF send and receive capabilities to minimize the number of BGP updates that are sent between BGP peers Helps to reduce the amount of system resources required for generating and processing routing updates by filtering out unwanted routing updates at the source Limits the number of unwanted routing updates, which will reduce the amount of resources required for routing update generation and processing Reduces the amount of resources required to receive and discard routes that would otherwise be filtered out

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-6 Sample: BGP Prefix-Based Outbound Route Filtering router bgp 100 address-family ipv4 unicast neighbor remote-as 200 neighbor ebgp-multihop neighbor capability orf prefix-list send ! ip prefix-list FILTER seq 10 permit /24 Router-A Configuration (Sender) Router-B Configuration (Receiver) router bgp 200 address-family ipv4 unicast neighbor remote-as 100 neighbor ebgp-multihop 255 neighbor capability orf prefix-list receive Rtra# clear ip bgp in prefix-filter

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-7 ORF format An ORF message consists of the following fields: –AFI/SAFI –ORF type –When to refresh –List of ORF entries ORF entries depend on the ORF type. The ORF capability needs to be negotiated for every supported ORF type. Outbound Route Filter Message

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-8 Outbound Route Filter Message (Cont.) ORF types: NLRI (ORF type = 1) –Filters based on the prefix Communities (ORF type = 2) –Filters based on standard BGP community attributes Extended communities (ORF type = 3) –Filters based on extended BGP community attributes Prefix-list (ORF type = 128) –Filters based on Cisco implementation of prefix filtering

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-9 AFI/SAFI is IPv4 unicast. ORF type is NLRI: Action: ADD, DELETE, or DELETE ALL Match: PERMIT or DENY Scope: EXACT or REFINE NLRI: Prefix When: IMMEDIATE or DEFER Outbound Route Filter Message (Cont.)

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-10 neighbor ip-address capability orf prefix-list [receive|send|both] router(config-router)# This command enables negotiation of prefix-list ORF capability during session setup. The ORF-capable BGP speaker will install ORFs per neighbor. Option: -“Both” allows sending and receiving of prefix-lists. -“Send” allows only sending of prefix-lists. -“Receive” allows only receiving of prefix-lists. Configuring Outbound Route Filtering

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-11 The command capability orf prefix-list send on one router requires capability orf prefix­list receive on a neighboring router. Configuring Outbound Route Filtering (Cont.)

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-12 Using Outbound Route Filtering clear ip bgp neighbor in [prefix-filter] router# This command triggers a route refresh message. This command includes a prefix-list in the route refresh message if configured and supported on both ends. The prefix-list is sent at session setup. Use the prefix-filter option to refresh the remote filter.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-13 Monitoring Outbound Route Filtering show ip bgp neighbors neighbor router# Verifies the supported capabilities

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-14 Summary Outbound route filtering is a mechanism that is used to minimize the number of updates that are requested from a neighbor. The BGP prefix-based outbound route filtering feature uses BGP ORF send and receive capabilities to minimize the number of BGP updates that are sent between BGP peers. Configuring this feature can help reduce the amount of system resources required for generating and processing routing updates by filtering out unwanted routing updates at the source. The ORF message contains the information that is used to determine which updates will be passed. The format of an ORF message includes AFI and SAFI for which the filter should be used; ORF type, which identifies the type of filter; when to refresh (immediate or deferred refresh); and a list of ORF entries where the actual filter is defined.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-15 Summary (Cont.) The neighbor ip-address capability orf prefix-list command with the send and receive keywords enables ORF negotiations and activates an ORF prefix-list. Use the clear ip bgp neighbor command to trigger a BGP route refresh. With the show ip bgp neighbors command, neighbor- supported ORF capabilities are displayed as “advertised, received,” and a filter of the supported type can be sent to the neighbor.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—3-16