BGP Outbound Request Filter Capability
BGP ORF, enabled by BGP Capabilities (discussed in Chapter 5), helps conserve resources during BGP route update processing. If the ORF capability is advertised by a neighbor during session establishment, this means that the local BGP speaker will allow its neighbor to push over its inbound prefix filter. After it's received, the local BGP speaker installs the filter, in addition to any locally configured outbound filters associated with the neighbor.
Several benefits are associated with BGP ORF:
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The local BGP speaker will no longer consume resources generating routing update messages that will be filtered by the neighbor on input.
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Link bandwidth will not be consumed by the routing updates.
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The neighbor router will not need to consume resources processing routing updates that will be discarded once a filter lookup occurs.
Note
It's important to understand that the impact of BGP ORF can be quite significant. For example, if a BGP peer were to send a global Internet routing table (more than 75,000 routes today) to a low-end router that is limited in memory, it might cause this router to run out of memory even if the router has inbound filters installed. Also, sending the routes to the neighbor can consume a significant amount of link bandwidth on lower-speed connections.
This is ideal for ISPs with automated route filter-generation tools and routers with lots of BGP peers. Once the filter is generated and deployed to the edge router in the ISPs network, it is pushed over to the customer's router, thereby conserving both customer and ISP resources.
By default, the ORF Capability is not advertised to neighbors. Also, BGP ORF cannot be advertised to a neighbor that's a BGP peer group member.
As a result of varying BGP ORF syntax across different versions of IOS, we've decided to include Appendix C, "BGP Outbound Route Filter (ORF)," that contains the Cisco release notes associated with BGP ORF. For additional information, consult the documentation specific to your version of IOS.